CA2123226A1 - Lamp brightness control circuit with ambient light compensation - Google Patents

Abstract

A compact auxiliary circuit (300) modifies the operation of a low-voltage control circuit (42) associated with an electronic dimming gas discharge lamp ballast (2). The auxiliary circuit (300) modifies the output of the control circuit (42) to reduce the brightness of the lamps (26) when excess ambient light is available, and increases the brightness of the lamps (26) as available ambient light is reduced. The auxiliary circuit is located in a small housing (312) which mounts in a knockout plug of a fluorescent ceiling fixture (501). In a preferred embodiment, the auxiliary circuit (300) includes a photocell (308) that obtains information on ambient light levels through an ambient light gathering prism (302) mounted through a ceiling tile (508) near the fixture (501), and connected to the circuit housing (312) by a flexible fiber optic cable (306). A single auxiliary circuit (300) according to the invention can be connected to vary the brightness of a large number of lamps.

Description

W O g3~09649 PCT/US92/~9746 LA~P BRIGHTNESS COMTROL CIRCUIT
WIT~ AMBIENT LIG~T CONPENSATION

This application is a continuation-in-part of U.S. Patent Application Serlal Number 07/410,480 filed Sept~mber 21, 1989.

Field of the Invent1gn The present invention relates broadly to a circuit for controlling the brightness of a ~amp to maintain a desired ambient light level in an area, despite variations in the amount of light supplied by a source eYternal to the circuit.

~ack~round o~ the Invention recent years, the fluorescent lamp, ~hich requires les~ energy tha~n the incandescent la~p to produce ~he same amount of light, has enjoyed increa~ing popularity. In many modern offices, fluorescent lamps are used to the complete exclusion of incandescent lamps. Other gas discharge la~ps, such as:sodium-vapor lamps, have replaced incandesoent lamp~ in outdoor lighting applications.
To ~aintai~ high energy efficie~cy, reliable operation, and long lamp life,~ these: gas di~charge la~ps may be operated in conjunction with a reson~ant in~erter ballas:t circuit, such a : the ballast sho~n in the nvent~r's U. S.:Pate~t 4,933,605.
Electro~ic dim~ing control circuits, such a~ the circuit disclosed in the inve~tor'~ cope~ding U.S. Patent Applica~ion Ser~l Nu~ber 07/410,480 filed Sep~ember 21, 1989, haYe been used ~ith resonant inverter ballAs~s ~o proYide effective low-vol~age co~trol of gas discharge lamp brightness.
In the preferred embodiment of: the dimming circuit disclosed in the 071410,480 applicatio~, the dim~Lng level is controlled by a lo~ voltage input level produced~by in~egrating a varisble pulse ~idth output rom an electronic dimming control circuit.
Such clectrQni dimming circuits are generally provided with an operator-~djusted manual control for setting :the desired level of gas discharge lamp luminosity. ~It is also known tG turn lamps on and of~ in re~ponse to pho~ocell measurement of ambient light levels. In a co~mon application of this tech~ique, a photocell may ~e used to turn on a W O 93/OgS49 PC~/USg2/09746

2 1 2 3 2 2 6 ~ ~rv parking lot lamp during periods of darkness (i.e. night) and to turn the lamp off during periods when sufficient eYternal light sources (such as sunlight~ are available, thus con~erving energy.
In an office settiRg, each work are~ must at all times be provided with at least a minimum level of light. The minimum necessary light level is determined based on the tasks performed in the area. Fluorescent lamps are generally installed in size and number sufficient-to provide the minimum required light level in an area unter the asYumption that no other light sources w~ll be available. A dimming circuit may be provided to adjust the light output o~ the lamps, permitting multiple uses of the area :
and compe~sation for changes in external light.
At times, other light sources are also operating in the area so that ,~ :
the amount of light produced i8 more than is needed, and the operation of the lamps at the same intensity used in the absence of other light sources is a waste of energy. ~For eYample, during the day sunlight may enter through windows and skylights. When these other light sources are available, the preset brightness of the gas discharge lamps will not be . ~
needed in its entirety sincu the eYternal light source provides some or ll of~ the minimum needed li~ht in the area. It would be passibl~ to conserve 1arge quantitiès of energy, possibly up to 30Z of the energy used to light a typical office building, if the light output of gas discharge la~p~s could be limited~at all tlmes to the minimum required level.
Additionally, ~i~n~the workplace, it is usually desirable to have a constant level~of light on ~ork surfaces. Contin~slly changing light levels~resuIt in~pe~riods~of glare~when too much light is provided and period of lncreased~diffLcu}ty in resolving images when too little light is~pro~ided. A ~orker's~eyes must adjust to xesolve images at a gi~en light ~level.~ ~Thus,~cQntinual light level variations requires continuous optic~compen8atl0n,~and~thi;s eyestrain over time can adversely affect health and;productivit~
~, U.S. Patents 4,48Z,844 to Sch~eer et al., and 4,371~812 and 4,394,603 to ~idmayer, show systems for dimmlng a fluorescent lamp in response to ambie~t light condl~tions.~U.S. Patent 4,464,606 to Kane discloses a fluorescent lamp dimmer with an electronic inverter that is controlled in re6poDse to signals from~a celling-mounted ambient light sensor. The dimming control circui~ sho~n operstes using low voltages and pulse width modulation of the power to the lamps, but does ~ot integrate pulse-width modulated control si~nals to produce the dimming control signal that co~trols the vidth of the~ lamp svitching control pulse5. As far as the W O 93/09649 PCT~S92/09746 ,~ ~ 3 ~ 2 ~ 2~ 2 2 ~

inventor is a~are, electronic dimming control circuits of the type disclossd in the aore~entioned pending application have not bee~
equipped wi~h circuits for adjusting the lamp output to mi~imize energy consumpt~on while main~ai~ing a constan~ light level in an area.

SummarY of the Invention Therefore, it is a general object of the present invention to provlde an energy saving control circuit for gas discha~ge lampsO
~ other broad object of the present invention to pro~ide a circuit ~hic~ maintains a constant desired light level in an area.
A further object of the present invention is to provide a control circuit for one or more gas~ discharge lamps ~hich maintains a constant light level in an area by measuring the ambient light and reducing the output of the lamps by the amount of light contributed by external light sources.
Another important ob~ect of the present inventio~ is to provide a lo~
voltage ambient lipht monitori~g circuit having lo~ power requirements hich can be ~ged to control a plurality of el~otronic balla ts to dim balla8ted lamps~in response to the ambient light level.
Other o~ject~ of the invention will become Rpparent upon revie~ of the;specification, dra~i~gs, and claims.
Thsse objects~and others are;achieved by providlng a comps:ct, easily s~talled au~iliary circuit~uhich operates ~ith a lo~voltage co~trol circuit associated vith~an electronic dimming lamp ballast. The auxiliary c~rcuit:mo:difies the output of the control circuit to reduce the brightness~ of the lamps~when excess ambient light i8 a~ailable, and increases~the br~ghtne6~ of the lamps as available ambient light is reduc~d. ~The auxiliary circuit is located i~ a ~mall housi~g whlch mounts in a knockout~ plug of a `fluorescent ceiling fi~ture. The au~iliary ::
cirouit includes a photocell ~ha~ obtains information on ambient light levels thr~ugh an a~bient light gathering prism mounted in the ceiling near the fixture, and~connected to the circuit housing by a flexible fiber optic cable. A sialgle circuit according to the invention can be used to ; control multiple ballasts~
~ ::
, ~ ~

O 93/0964~ 3 2 2 6 4 _ PCT/US92/09746 Brief Descri~tion of the Dra~inQs Figuxe 1 is a circuit dia8ram of 8 solid-state electronic ballast circuit sho~ing a pu~se-~idth modulation dimming control ci~cuit connected to control the ballast;
Figure 2 is a detailed circuit diagram of the pulse-width mod~lation dimming control circuit shovn in Figure l;
Figure 3 is a block-schematic diagram of the ambient-light responsi~e control circuit of the present invention;
igure 4 is a schematic~diagra~ of the ambient-light responsive electronic control circuit shown~in Figure 3;
Figure 5 is a diagram showing installation of the system of the present i~vention in conJunctioD ~i~h a fluorescent ceiling fi~ture; and Fi~gure 6a is a frontal~viev of the light-gathering prism of the present invention, ~hile~Figure ~6b is a corresponding side viev of the ame prism. ~ ~

Detailed ~escri~tion~of~the Preferred Embodiments The~'lamp~ballast and~dimming circuit -i h which the present invention may~be used ill first~be described ith reference to Figures 1 and 2.
Referring first;to~Figure 1, a resona~t :inverter solid-state dimming bàllast~circult;is sho~n generally at 2. While a brief'description of the co~n~truction~ and operation~of~this circuit; will be provided here, the soiid~stat'e~dimming~ballast~2 is described;~completely in the inventor's U.S.~patents~ 4,~993,605~and~4,~B64,482, the disclosure6 of which are incorporated here *~by~reference.
;As~ ho~n~in~igure;l,; the~solid-state dim~ing ballast 2 comprises pulse~idt~;modulator 4~, po-er ~s~itche6 6~a~d~8, resonant inductor 10, reso~ant capacitor 12,~blocking capacitor 14, voltage diYider resistor 16, v&riable re6istor 18, oscillator resistor 20, oscillator capacitor 22, and oad~26.~ ~Load 26 is~provid~d with four terminals 38~ 39, 40 and 41. The load 26 may ~pre~ferably be~ a~' fluorescent~ tube and ~ill frequently be described as such herein.
The ~pulse width~modulator 4 may be a~conventional integrated circuit such~as~a Motorola SG-2525, used ith~the~follo-ing termi~al connections:
Vcc (pin 15) is connected to a DC voltage sosrce 24, ~hile the Ground termi~al (pin 12) is~connected to ground. The RT terminal (pin 6) is : :
~ connected throug'h 0~6cillator resistor~20 to ground, and the CT terminal W O 93/0964g PCT/US~2io9746 - 5 - 2 1 2 3 ~2 ~
(pin S) is connected through the oscillator capacitor 22 to ground. Vref ~pi~ 16) is connected to one terminal of ~oltage divider resi~tor 16. The other texminal of voltage diYider resistor 16 is connected to the Noninverting Input 17 (pin 2) of pulse width modulator 4 and also connected to ground through variable resistor 18. Output A ~pin ll) and Output B (pin 14) of pulse width modulator 4 are connec~ed respectively to control terminals 33 and 29 of power svitches 8 and 6 respectively. For reasons ~hich will ~-ecome clear upon description of further circuits useful with the circuit of Figure I, the two terminals of variable resistor 18 are preferably connected to terminals accessible from the outside of any housi~g enclosing ballast 2 so that external circuits can be connected to the~e terminals.
The po~er switches ~6 `and 8 may be of any suitable solid-state or mechanical construction. Power svitch 6 is provided with two switching terminals 28 and 30, ~nd power switch 8 likewise has two switching terminals 32 and 34. Each of the power switches 6 and 8 are also provided with control terminal 29 and 33 BS ~escribed previously. I~ response to ~;
a signa~ pulse on the control terminal '9 produced by the pulse ~idth odulator 4, the pover switch 6 vill inte ~ally connect poYer terminals 28 and 30 ~o that devices~connected to~power terminal 28 ~ill be electrically connected~with devices~connected to power termLnal 30. The power s~itch 8 1ike~ise connects power termina1s 32 and 34 in response to a signal pulse fro-~the~pu1se vidth~modulator 4 transmitted tO the control terminal 33 of power~switch 8~
A~ pos~itive~DC source; 36~is~connected to power terminal 28 of power switch;~6~, and~pover terminal 30 is connected both tD the pover terminal 32 f power s~itch 8 and~to~one terminal of resonant inductor lO. The other terminal of~resonant~ inductor ~lO is connected to terminal 38 of load 26.
Po~er term ~al 34 of po~er switch 8 is connected both to ground and to one termlna~l;of~the blocking capacitor 14. The other termina1 of blocking capacitor 14 i8 connected to terminal 40 of fluorescent tube (load) 26, the terminal 40~being~at th~ opposite end of the tube from ~erminal 38 The`resonsnt capacitor~12 is~c~onnected across terminals 39 and 41 of the fluorescent tube 26. m OsciIlator resistor~20 and oscillator c~pacitor 22 together control the ~requenc~ o~ the internal oscillator of pulse width modulator 4, ~hich in turn controls the frequency of the output pulses from Outputs A and B
(pins tl and 14) of the pulse width modulator 4, which in turn control the switchi~g of po~er to the fluorescent tube 26 as will be explained later 21~322~i WO 93/09649 ~CI`/US92/09746 in more detail. Thus, the values of oscillator resistor 20 and oscillator capacitor 22 are chosen to provide the desired frequency of po~er ching at fluorescent tube 26.
The po~er switches 6 and 8 are alternately actuated by the signals Bt control terminals 29 and 33 respectively. In operation, po~er s~itch 6 is actuated first, so that DC current flows from DC source 36 through resonant inductor 10, load 26, and resonant ~apacito~ 12, charging blocking capacitor 14. Power switch 6 is then deactuated. After a brief period of ti~e, po~er witch 8 is actuated, so that stored charge flows from blocking capacitor 14 through load 26, resonant capacitor 12, and resonant inductor 10 to ground, thus discharging blocking capacitor 14.
After a brief time delay this cycle is repeated, with the repetition at a constsnt frequency determined by the values of oscillator resistor 20 and oscillator~ capaci~or 22 as explained previously. The repetition of this switching operation produces aD alternating current flow through load 26.
When the load 26 is a fluorescent tube, this current flo~ will excite the internal gases of the tube, caus~ng the tube to glo~.
The amount of time~bet~een repetitlons of the cycle just explained is dete~mined by the duty cycIe of the control pulses~produced by pulse ~idth odulator 4 and transmitted to control terminals 29 and 33. As the duty cycle of the control pulses increases, the duty cycle of pover applied to he lo~d 26 will increase, increasing the apparcnt brigh~ness of the fluorescent tube 26. C onverBely~ as the duty cycle of the co~trol p~lses decreases, the apparent brightness of the fluorescent tube 26 ~ill decrease. Thus, the circuit can be used to produce a dimming fu~ction.
The~ duty oycle of~the control pulses ~produccd by pulse width modulator 4 is varied by~varying the voltage applied to the non-inverting input 17~ of pulse ~:idth~modul~tor 4.
Ths dimming control circuit used in the di~ming ballas~ circuit o~
Figures l and 2, comprising~ pulse generating circuit 42, will no~ be described in detail.
As shown in Figure 1, pulse generating cirruit 42 is connected as a control input to the resonant inverter solid-state ballast 2. The output 43 of dimming control circuit 42 is connected to opto-isolator 48. If no isoIation is desixed, output 43 could also be directly connected to the base of an ordinary transistor substituted for phototransistor 52 and having the same emitter a~d collector connections as phototransistor 52.
Opto-isolator 48 comprises a light-emitting diode (LED) S0 and a phototransis~or 52. LED S0 is connected between o~tput 43 and ground.

W 0 ~3/09649 2 1 2 3 2 2 6 PcT/us92to974~

Phototransistor 52 has its collector connected to non-inverting input 17 and its emitter connected to ground. Phototransistor 52 turns on in response to light emis~ions from LED 50, which operates in response to the pulses fro~ output 43. Opto-isolator 48 thus electrically isolates the ballast 2 from the pulse generating circuit 42. ~he ballast circuitry may contain large voltageæ and current, and as will be seen, controls for the pulse generating circuit 42 will be handled by human operators. Thérefore, this electrical isolation provides a substantial safety benefit.
The collector of phototransistor 52 is connected to non-inverting input 17 of pul~e width modulator 4, while the emitter of phototransistor 52 is connected to ground. An integrating capacitor 46 is connected between the non-in~erting input 17 and ground. The pulse generating circuit 42 preferably generates a variable duty cycle, square wave pulse ;train at a fixed frequency greater than 1 kHz.
The output puIses at ~output 43 control the charging of integrating capacitor 46. ~hen pulse generating circuit 42 produces a pulse at output 43, t~he voltage applied to the base of transistor 44 turns on phototransistor 52, allowing~current to flo~ from the collector to the emitter of~ the transistor 44~. Because the collector of phototransistor 52 is connected to the capacitor 46 and the non-inverting i~put 17, and since the~ emitter of phototrans~istor 52~ is connected to ground, a pulse from pul:se generating circuit 42;effectively grounds the integrating capacitor 46~.~ tend~ing~to discharge~the capacitor 46. ~hen output 43 is not producing a pulse,~ phototransistor 52 is turned off, and integrating capacitor 46 te~ds to~charge to the~ level of the voltage drop across variablè resistor~ 18 ~as~determined by the voltage divider comprising resi~tor 16 and~ariable~resistor 1~. ~
T~e~voltage ~t~non-inverting input 17 ~aries with the duty cycle of the pulses at output 43. Since the output 43 prcduces a serles of pulses at high~frequency. ~he~pulses produce a periodic pull up and down of the `~ DG level across integrating capacitor 46. Integrating capacitor 46 integrates over time he DC level shift produced by the pulsed output 43, so tha~t for~a given pulse duty cycle, a continuous DC voltage appears at ~on-inverting input 17. The DC voltage at non invertîng input 17 will :: :
vary with the duty cycle of the pulsed output 43 in the follo~ing manner.
As the duty c~cle ~ncreases, the capacitor 46 will be grounded for a relatively greater portion o~ time, and the voltage at non-inver~ing input , 17 ~ill be reduced. Con~ersely ? as the duty cycle of pulses at output 43 ~ is reduced, the voltage at non-inverting input 17 ~ill be increased.
:~:

W O 93/Og649 PCT/USg2/09746 2123~2~ 8 - ,<~c~i Because the ~oltage level at no~-inverting input 17 controls the apparent brightness of load 26, those skilled in the art will immediately appreciate that the light output of load 26 can be adjusted by ~arying the duty cycle of the pulses at output 43. Thus, the dimming of the solid-~tate ballast is controlled by varying the duty cycle of a low-voltage pulsed input to ths control circuitry of the ballast.
The circuit and operat~on of the pulse generating circuit 42 will now be described in det&il with reference to Figure 2. As sho~n in Figure 2, the pulse generating circuit 42 comprises a power supply section 54, a reset section 56, a delay section 58, ~n overcurrent section 60, a pulse control section 62, a brightness control section 64, and a variable duty c~cle ~requency source 65.
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The ~ariable duty cycle frequency source 65 may preferahly be an UC2843 integrated circuit~ manufactured by Motorola, although other integrated circuits could be~used, or a circuit could be constructed to perform the necessary functions. The operation of the frequency source 65 is descri~ed in detail~in Motorola publlcations ~hich will be familiar and accessible to those ~skilled in;the art. Ho~ever, the fu~ctions of the pi~s~used~in this circuit~are~described in Table 1 in sufficient detail to permit those~s~illed~in the rt to understand the circuit and to practice the invention disclosed.~

Pin Connections of UC2843 Frequency Source PIN NAME~ DESCRIPTION ~ ~
C`ompensation Voltage~may be applied exte~nally to vary the duty cycle~of~the pulses. ~ ~
2~ Inv.~Input ~ ~ Not Used (~connected to~ground).

3 ~urrent Sense Inhibits~pulse output if~:more than one volt is applied e~tern-lly.

4~ ~OSC ~ Provides~sa-tooth~wave output ~ith frequency depending on~external circuitry.

5 ~ ~Ground ~ Connected~to ground.

6~ ~ 0ùtput ~Produces~variable duty cycle pulse output ~ith frequency depending on external circuitry coDnected to OSC terminal and duty~cycle depending Qn voltage applied to Compensation terminal.

7 Vcc Power supply (+12v DC).

8 Vref Reference voltage output t5.1 VDC).
TABLE~l .

W093/09~g 9 2 1 2 3 2 2 li Pcr/lJs92/o9746 Referring again to Figure 2, the power ~upply section 54 comprises a transformer S6, a full-wave bridge rectifier 68, a capacitor isolation diode 70, and a smoothing capacitor 72. The pover supply section 54 is preferably al~o provided with a conventional three-termi~al, 12 volt voltage regulator 84 a~d a~ associated capacitor 86. The voltage regulator 84 ha an input texminal 88, an output terminal 90, and a ground termlnal 92.
Alternating current input from an AC source 74 is connected to the prlmary coil of transformer 66. The turns ratio of transformer 66 is seleeted ~ith reference to the voltage of AC source 74 so that 12 volts AC
produced on ~he seco~dary coil. Full-wave bridge rectifier 68 is a conven io~al device. The rectifier 68 has t~o lnput terminals 75 and 78 a~d t~o output terminals 80 snd 82. The tvo terminals of the secondary coil of transformer 66 are ronnected respectively to input terminals 75 and 78 of rectifier 68. Output terminal 80 of rectifier 68 is connected to circuit and Earth ground, ~hile output terminal 82 is connected to the anode of isolatio~ diode 70 and provides a rectified, 12 vclt DC output hareto. The cathode of dioda~70 is con~ected to the input terminal 88 of :regulator 84 and to the positive ter~inal of s~oothing capacitor 72. The negative terminal of~smoothing capacitor 72 is connected to both circuit ground a~d Earth grou~d.
Tha output termi~al 90 of regul-tor 84 is connected to Vcc (pin 7) of varlabla duty cycl~ ~frequancy source 65, a~d ground terminal 92 is co~ected to ground~. The :capacitor 86 is connected betueen the output :
ter~i~al 92 ~f regulator 84 and ground. The voltage regulator 84 co~pensd~es for ~ rl-t~ions~ in the~ voltage of AC source 74, thus tabilizing tha 12 volt~DC pover provided to ~he integrased circuits of freqna~cg:~sourca:65. ~ st6ble voltage supply for frequency source 65 is ece~ 8 ary to:-void: ~a:ri-tio~s in the pu18 e sig~al output 43 of ~he frequency source:65.: :
: ~ Pr~ferably, the 12 volt DC regulated output at output terminal 90 of ~ regulator 84 wil~ be us~ed as the DC source 24 connected to Vcc of the- ~ ; pulse width modulator 4 (shown in Figure l). In this vay 9 the entire circuit ma~ be controlled by a single po~er s~itch ~not: shown in the : : drawings). This ~itch may be any conve~tional switch and may be talled in ths pover supply circuitry in a number of ways which are ~; conventional and ~ill be immediately apparent to those skiiled in ~he ar~.
: The brightness c~o~trol section 64 comprises a variable resistox 94 and a voltage divider resistor 9S. The v~riable resistor 94 is connected W 0 93/Og649 2 1 2 3 2 2 6 lo PCT/US92/09746 between the compensation pin (pin 1) of frequency sOuEce 65 and ground.
Preferably, for reasons which ~ill become more obvious, the two terminals of variable resistor 94 will be connected to terminals on the outside of 8 housing contaîning electronic dimming circuit 42 and/or ballast 2 so that uires from external devices can bejconnected to the terminals of variable resistor 94. ~oltage divider resistor 96 is connected bet~een Vref (pin 8) of frequency source 65 and the compensation pin (pin 1) of freque~cy source 65. Vref (pin 8j of frequency source 65 provides a constant S.l ~olt DC signal. Thus, the variable resistor 94'and resistor 96 form a .- :
voltage di~ider so that, as the variable resistor' 94 is adjusted, the ~oltage applied to the compensation pin (pin 1) of frequency source 65 will vary. As explained in Table 1, the voltage on the c~ompensation pin (pin 1) of frequency source 65 controls the duty cycle of the pulses produced at output 43, ~with the duty cycle determining the brightness of the load 26 as described previously.
The po~er supply s~itch previousl7 described may be integrated ~ith the variable resistor 94 in~a;manner well known in the art.
The delay section ~58 comprises a PNP transistor 98, a resistor 100, capacitor 102. and resistor 104. The emitter of transistor 98 is connected to~the~eompensatiQn~terminal ~pin l) of;~frequency source 65, while the collector of~trans`is~tor 98 is~connected to ground. The base of transistor ~,',c~ 98~is~;~conneoted~to one terminal of resistor 104, and the other terminal of t~e~resis,tor 104 ~is;~c~onnected to the output terminal 82 of bridge ,`'réctifier 68. ~The posltive~terminal of;capacltor lQ2 is connected to the bà,se~;of~transistor~98~ ;whil~e~ the negative~terminal of capacitor 102 is conneSted~to;~ground. ~Resistor 100~ is connected between the base of trans~i8tor~98~and~ground.~
s~will~be~seen.~the~delay~section S8, provides advantageous operatioh becausé.~in~;operation,~tbe~del~y section 58 suppres~es~trans-ission of the d~mming signal at output~43~ at po~er-up. With ~the dimming signal ` suppressed by dela~'section 58,~ the tube 26 ~shown in Figure 2) is started~ at full brightness.~Full-brightness starting is,essential for two reasons:
s , ~ First,~full-brlghtnes~s starting prolon~gs the life of the fluorescent tubes~.~Second, fluorescent tubes ~may not start at all if power is not provided for the full~duty cycle.
The operation of~delay~section;58 to suppress ~he dimming s~gnal at output 43 ~ill no~ be~described in detail. ~hen no power is applied to the circuit 42 from AC source 74, the transistor 98 ~ill conduct fully, , " ~ ~
~ ; thus effecti~ely grounding the compensation terminal ~pin 1) of frequency W 0 ~3/09649 ~ 2 ~ 2 3 ~ 2 6 PCT/U~92/09746 source 65. ~hen the compensation terminal is grounded in this manner, a zero duty cycle at output 4~ is selected. As explained previously, the brightness of the load 26 (shown in Figure 2) varies inversely with the duty cycle of the pulsed output 43. A zero duty cycle of the pulsed output 43 corrssponds to full brightness at the load 26 (6hown in Figure 2~.
Therefore, ~hen the transistor 98 is fully conductive, the load ~6 will be at ~aYimum brightness.
When power is applied to the circuit 42, the capacitor 102 will charge according to a time constant determined by the values of resistors 100 and 104 and capacitor 102. As the capacit~r 102 charges, the transistor 98 will be rendered less conductive, u~til the transistor 98 cèases to conduct. ~hen the trsnsistor 98 ceases to conduct, the delay section 58 will have no~effect OD the voltage at the compensation pin (pin 1) of frequency source 6S:.~ The ~oltage at the compensation pin (pin 1 will then be controlled entirely by the brightness control section 64.
Thus,~when power is applied to the circuit 42 and the resonant inverter 801id-state ballast 2 (shovn in Figure 1), the delay section 58 will initially inhibit;any~dimm~ng of the load 26 (as shown in Figure 1), regardless of:the setting of variable resistor 94 (the brightness control)~ The Ioad 26~:~wi11 nstart~ at full brightness. After a brief period of time, the délay section::S8 will cease to inhibit dimming and the load 26 ~ill dim to the: leve~l~se~lected by means of variable resistor 94.
The :fluore~scent: lamp 26 does: not come on at full brightness and then sudden~ly~become dim;~the;~steadily increasing ~oltage across capacitor 102 :as:~ charg2s reduces~the:conductance of transistor 98 steadily o~er a brief:~period:of time. ~ The;~voltage at the compensation pin (pin 1) of frequency sou~rce 65 will therefore increase steadily fro~ zero to the level determined by~the~setting~of variable~resistor 94. hs a result, the fluorescent~lamp~26 wi11~comè on at full brightness, and then dim to the pre8et level in a smooth~;~and pleasing ma~ner.
The length of the delay produced by delay section 58 can be adjusted by changing the value~of~resistors 100 and 104 and capacitor 102 in accordance;with well-known~time constant principles.
During a po~er failure,~fluorescent lamp 26 wil} be e~tinguished. If the power failure is brief,~the capacitor 102 may retain its charge, so that delay section 58 will not provide the desired full-brightness startup and transition to the~ set dimming level as described. As eYplained previously, the ~amp 2:6:may not star~ at a low-brightness setting, and even~ if the lamp 26 does start, its life ~ill be shortened by a low-W O 93J0g649 2 1 2 3 ~ 2 6 12 - PCT/USg2/09746 intensity startup. Reset section 56 operates to reset the delay section 58 during a po~er fa~lure, preparing delay section 58 to operate properly vhe~ power is re~urned to the circuit.
Reset section 56 comprises a diode 106, resistor 108, PNP transistor 110, filter capacitor 1129 and voltage divider resistsrs 114 and 116. The anode of diode 106 is connected to the base of delay section transistor 98,~and the cathode of diode l06 i~ connected to one terminal of resistor 108. The other terQinal of resistor 108 is connected to the emitter of transistor 110. Resistor 108 preferably has a small value, in the range of 5-7 Ohms. The collector of transistor 110 is connected to ground. The positive terminal of filter capacitor 112 is connected to the base of transistor 110, while the negative terminal of the capacitor 112 is connected to ground. One terminal of resistor 114 is connected to the output~terminal 82 of ful~-~ave bridge rectifier 68, while the other terminal of the resistor 114 is connected to the base of transistor 110.
Resistor 116 is connected between the base of transistor 110 and ground.
.
Resistors 114 ~and 116 together form a voltage divider which de~termines the voltage~at the base of trahsistor 110. The values of resistors 114 and ll6 are chosen with reference to the values of resistors 100 and~104 so that transistor 110 does not conduct while ~C power source 74 is~pro~:ding~power~to the circuit;42. The value of cap~citor 112 is chose~wlth~reference to;the values of resistors 114 and ll~ so that, if power~is removed from the circui~t, capacitor 112 ~ill discharge through resistor;116~in~about~1 millisecond.
If a;~failure of~power~from ~AC source 74 occurs, the reset section 56 op~erates~as ollows~ The~ voltage at the base of transistor 110 falls to zero ~ vlthin one~ milli:se~cond as the capacitor 112 dischar~ges through iesistor ll6.~;Bec~u6e;delar;~ection capacitor lQ2 is still char~ed, the voltage at the e~itter~of transistor 110 i8 considerably greater than sero~. ~ Therefore, transistor l10 begins to conduct, effectively shorting :
and discharging the delay section capacitor 102. Thus, the reset section 6~quickly prepares the~delay~section 58 so that the fluorescent tube 26 may be restarted automatical~ly at full brightness as descri~ed previously.
It should be~noted that diode 70 is provided in the power supply section 54 to isolate the reset section 56 from filter capacitor 72 so that, during a po~er interruption, filter capacitor 72 will not discharge :
through the reset section 56 and prevent proper operation of the reset section 56.
~ ~ The pulse control section 62 determines the frequency of the pulsed :' W 0 93/09649 - 13 ~ 2 1 2 3 2 2 ~ PCT/USg2/0974~

output 43 and limit~ the ms~imum dut~ cycle of the output pulses. Pulse control section 62 comprises NPN transistor 118, frequency set capacitor 120, ~requency se~ refiistor 122, resistor 124, vRriable resistor 126, and resistor 128. T~e base of transistor llB is connected to the oscillator terminal (pin 4) of frequency source 65. The collector of transistor 118 is connected to Vref (pin 8) of frequency source 65, and the emitter of transistor 118 is connected to one of the t~o terminals of resi.stor 124.
The other ter~inal of resi~tor 124 is connected to one of the two te~minals of ~ariable reslstor 126. The other termin~l voltage appLied to the current sense ter~inal (pi~ 3) will be approximately 1.4 volts.
The frequency source 65 will inhibit generation of a pulse signal at output 43 whenever the voltage applied to the current sense terminal (pin 3) is greater than about one volt. Therefore, the effect of applying a high frequency ramp oignal to the current sense terminal (pin 3) is to suppress pulse generation during a portion of each ramp cycle.
The ramp signal applied to the current sense terminal (pin 3) has a ; peak~voltage Vmax. As ~e~piained previously, due to the action of the voltage divider compri~ing resistors l24, 126, and lZB, Vmas is a fraction of the~peak voltage of the~ramp signal at the osc~llator terminal (pin 4) of~frequency~source~65. ~ Again, Vmax is preferably about 1.4 volts. A
single~ramp cycle~takes~place~over a time period encompassing a first time period~and a second time period. In the first time period, the voltage of the~ramp~ signal~rises~from~0~.6;vol~s to one volt; during this period, the frequency~source 65 is~not;inhibited from trans-itting a pulse at output 43.~ 0f course,~whether~or;not a pulse is transmitted by frequency source 65,~and;the~actual du~ration of any~pulse transmit~ed, are determined by brightness~control section 64,; delay section 58, and reset section 56 in the~mà~er~e~plained~previous~ly. Duri~g the second time period, the voltagé~ of~ the~ramp~signal applied to the current sen e terminal (pin 3) exceeds one volt, and the~frequency source 6s is inhibited from producing any signal at output 43,.~ Thus, the application o the ramp signal to the current sense terminal (pin 3)~ limits the maximum dutg cycle of the pulses at the output 43. In the~preerred embodiment described, with vmBx ~ 1.4 YoltS~ and vith the output~ 43 inhibited ~hen voltages greater than l.0 ~olts are applied to~the current sense terminal (pin 3) of frequency source 65, the maYimum duty c~cle of pulses at output 43 is SOX.
Limiting the pulsed output 43 to 8 50~ duty cycle places an upper limit on the amount of dimming of the load 26. This llmitBtion is ~ desirable because dimming the load 26 excessively may shorten lamp life ::
::

W O 93/09649 P~T/USg2/Og746 2 1~ 2 2~ - 14 _ and ~ill in some cases result in an unpleasant flickering effect when the load 26 i5 a fluoresce~t tube. The masimum duty c~cle of the pulsed output 43 can be adJusted u8~ng variable resistor 126, and may be set at a value othe~ than S02 as dictated by the requirements of the consumer or the design parameters of the ballast 2.
Overcurrent section 60 is a protective circuit that disables pulsed output 43 if excessive current is dra~n from output 43. Overcurrent Eection 60 comprises a resistor 134 and a diode 136. The anode of diode 136 is connected to an output reference 45 which may serve as the ground reference for the sig~al at output 43. The cathode of diode 136 is connected to the current sense terminal (pin 3~ of frequency source 65.
Resistor 134 is connected~between the anode of diode 136 snd ground.
iode 136 prevents transmission of the ramp signal at the current sense terminal;(pin 3) to the output reference 45.
The output 43 of frequency source 65 is inhibited when more than one volt is~applied to the current sense terminal (pin 3). The voltage drop across diode~136 is approxim-tely 0.6 volts; therefore, output 43 ~ill be inhibited if the voltage~at the anode of diode 136 is greater than 1.6 volts.;~ This condition~will occur ~hen the voltage drop across resistor 134~is greater than~1.6~volts. Preferably, resistor 134 may be a 4.7 O~m resistor, SQ that when more ;than 0.34 ~mperes of current is drawn from output 43, the voltage drop across resistor 134 ~ill be greater than 1.6 volts~and t~e~output 43~will be~disabled. Thus, the overcurrent section -60 prevents damage~to the circuit of the present invention.
Of~ course, e~ach~ballast 2~connected to pulse generating circuit 42 ill draw current, so~that~there is ~a~practlcal limit to the~ number of ballasts~;~2~that can;be controlled by a si~gle p~lse generating circuit 42.
The ~pulse generatin;g c~ircuit as~disclosed~ill drive approsi~ately 16 ball;asts without esceeding 0.34~mp curre~t dra~ from output 43. However, if it~is desired to~control more than 16 ballasts 2 using one pulse generating circuit 42, an NPN power transistor can be used to increase the fanout capability of~the~circuit 42. The base of the po~er transistor may be~connected to the output~43, while the collector of the po~er transistor is connected to a DC power;~source such as that provided at Vcc (pin 7) of frequency source 65. The pulse~signal output to the ballasts 2 is then take~ Rt the emitter of~the~po~er transistor. Numerous techniques of increasing fanout capacit~-o an output are kno~n in the art. and will not be described furth~er~ here. Thus, it can be seen that the fanout capability of the ci~rcuit 42 can be eYpanded to allow control of almost W 0 93/09649 - 15 - 6 Pc~/us92/~97~6 any number of ballasts 2 using well-known techniques.
According to ~he present invention, the circuits shown in Figures 1 s~d 2 may also incorporate ~n ambient light responsive se~sing and control circui~ 300, sho~n in block diagram form in Figure 3. Sensing and control circuit 300 is a means for varying the brightness of load 26 in inverse proportion to the amount of ambient light available rom other sources, sueh as daylight. As ~hown in Figure 3, sensing and control circuit 300 comprises light converging prism 302, attachment housin~ 304, fiber optic cable 306, ph~tocell 308, and processing circuit 310. Photocell 30~ and processing circuit 310 are contained in housing 312.
The converging prism 302 is connected to an end of fiber optic cable 306 and ~is arranged to ga her Dmbient light 314 and direct the light 314 into one end of fiber optic cable 306. Fiber optic cable 306 carries the àmbient light 314 from the end connected to converging prism 302 to its other end, which is connected to housing 312 vith this other end in close pro~imity to photocell 308. The light 314 passing through fiber optic cable 306 impinges on photoce~ll 308:so that the output of photocell 308 ~aries in response to the amount of light 314 gathered by prism 302, which varies~ith the a~ou~t of ~ambient light available. Photocell 308 may be a photoresistor which varles ~its~resistance in response to the amount of light imp~nging upDn it~ so that its ~output~ is a pair of terminals providi~g a varying resistance to a receiving circuit. For esample, ph~tocell 308 may be a photoresistor such as part ~umber CL7PS~L made by Claire~ Electro~ics Co. of Nount Vernon, New York. Thus, photocell 308 produces an output varying~vith the amount of ambient light available in the:area~oovered by~the collection field of prism 302. Prism 302 can be hsped~ as ~desired to colle~ct ambient light through a particular arc, either narrow, widet or inte~rmediate in ~idth.
The output af~photocell 308 is con~ected to process mg circult 310.
Processing circuit: ~lO produces: a co~trol output compatible with th~
ballast 2 to control the brightness of the load 26 depending on the amount of light available from other sources. If prism 3~2 is situated to sense only light from source(s) other than load 26, processing circuit 310 ma~
be constructed to reduce the brightness of load 26 depending on the amount of:light avail~able ~from the other source(s). Prism 302 ma~ also be constructed and located so as to sense the total light in the area (from .
~:: the load 26 and other sources). In particulart prism 302 may sense thetotal light reflecting from a critical work surface, such as ~ drafting table or desk, where a constant light level is desired. In such cases, W O 93J09649 PCT/US92/0~746 21232~6 - 16 ~
processing circuit 310 may be a feedback control circuit ~hich modifies the brightness of load 26 in respo~se to changes in the amount of light se~sed through photocell 308 to mainta~n a constant amount of light in the area, and thu~ a constan~ output of photocell 308. Such a feedback control circuit may incorporate proportional, integral, or derivati~e algorithms, or a combination of t~o or more of these algorithms or other algorithms commonly used in feedback control circuits. The output of processing r~rcuit 310 is connected to the ballast 2 by control line~ 316 uhlch carry signals to effect control of the brightness functions o ballast 2.
F:igure 4 is a schematic circuit diagram showing a preferred embodl~ent of processing circuit 310. It is possible to construct a feedback control circuit in accordance with the discussion above to pro~ide an amou~t of light in an area that is substantially constant, varying less than lZ from nominal. ~owever, in most practical office applications, such precise control is not necessary. ~uman eyes are r~la~ively insensitive to slight variations in light level~, and adjust re~dily to compensate for such variations. In addition, most ~ork areas are ~ot used for critical: detail ~ork. It has been found through experimen~ation that the total light in most work areas can deviate up to lOX from::the~ baseline level~without bein8 objectionable. Therefore, to i~imize cost, complesit~,:,and ~aintenance, the preferred embodiment provides a: relatively 6imple control:circuit which dims a controlled lamp in~response to an increase in externally provided light but does not measure total light directly to provide a~closed-loop feedback control ,~
8~:9tem. ~ : ~
In tbis ~embodiment,~ processing circuit 310 comprises,transistor 406, capacitor~ 40~:7 diode 410, capacitor 412, potentiometer 414, potentiometer 416, r~istor 418, ground terminal 419, a~d output te~minal 420.
Tra~si~cor 406 ~is ~i NPN transistor of the N3904 t~pe, snd diode 410 is of the lN914B type. Capacitor 408 is 0.01 uF; capacitor 412 is 47 uF;
resistor 418 is 27 kiloOhms; and potentiometers 414 and 416 are 100 kiloOhm potentiometers. Output terminal 420 and ground terminal 419 of processing circuit 310 together make up the control lines 316, and are con~ected to the ballast~2 in a mAnner that ~ill be described later in detail.
Photocell 308 is connected to the base of transistor 406. The collector of transistor 406 is connected to output termi~al 420~ and the emi~ter of transistor 406 is connected through potentiometer 416 to ground. D~ode 410 is connected between the base of transistor 406 and output terminal 420. Capacitor 412 is connected between the ba~e of transistor 406 and ground. Capacitor 408 is connected bet~een output terminal 420 and ground. Photocell 308 has two termiDal6. One termLnal of photocell 308 is connected to the base of transistor 406, and the other terminal of photocell 308 is co~nected through potentiometer 414 to output terminal 420 and through resistor 418 to ground. ~hile power/output term~nal 420 pro~ides ~the operating voltage necessary to operate processlng circuit 310, processing circuit 310 can also change the voltage at output term~nal 420 if the voltage applied is sensitive to the resistance of processing clrcuit 310. Thus, po~er/output terminal 420 is both a source of power for, and~an output of, processing circuit 310.
Depending on the intensity of the ambient light, photocell 308 changes its~ resistance, producing a higher resistance at low light levels and a lo~er resistance at~ higher light levels. Resistor 418 and potentiometer 414 together form a voltage divider, dividing the volsage applied through output ter-inal 420 so as to set the voltage applied to photocoll~308. This voltage divider determines the base-to-emitter turn-on voltage of the transistor 406. The resistance of the photocell 308 to the~applied~volt~age ~determines the current flo~ing into the base of transi tor 406.~ ~hen~the base~current of transistor 406 increases due to an~ increase l~ thè~ mbient~light level sensed~by photoeell 308, the col~lec~tor-to-emitter~current~in~transistor ~406 is increased. The ;po~er/~output~terminal;~420~ ill generally be connected to the middle of a voltage~divider~reslstor~net~ork havi:ng a voltsge source with limited current ~supplying capacity~. As a~result, ~hen~tran5istor 406 turns on, dèpe~ding;o~ the~flow~of;curreDt~to the ba~e~of transistor 40S, the output of~the~oltage source~cQnnected~to po~erjoutput terminal 420 ~ill begin to ;collapse.~ Thus,~the~magnitude~of the volt-ge at~po~er/output terminal 4~0 ~ill be reduced.
Potentiometer 416 can be used to 5et a ma~imum di~ming point~ i.e. to adjust;the amount of~dimming produced by the~ proces~ing circuit 310.
Potentiometer~416 must be~adjusted so that the masimum dimmin~ level ~ill not~result in turn-off of the load 26. The choice of the capacitance of capacitor 412 and the res~is ance of photocell 308 determines the delay or response time or variati~on of the load brightness in response to varistion in externally supplied light. Diode 410 operates to remove charge from the capacitor 412 within about 47 milliseco~ds after the po~er to ballast 2 is turned off, i.e. when ~Vref is removed. This operation : , :;: :::

W O g3/09649 PCT/US92/09746 reset~ the circuit 310 to provide full lamp brightness ~pon reactivation of ballast 2. Thus, diode 410 i8 a means for resetting the circuit to ensure that the fluorescent lamp is al~ays stsrted at full intensit~ to pro~ote reliable starti~g and longer lamp life.
Power/output terminal 420 will be connected to the circuits of Figure 1 and/or Figure 2, depending on the desired configuration and the nu~ber of ballasts to be controlled by sensing and control circuit 300. It is a particular advantage of the present invention that a single low-voltage, lo~-power sensin~ and control circuit 300 can be used ~ithout substantial modification to control one electronic ballast 2, or a l~rge number of electronic bal~asts 2.
Re~erring to Figure 1, if the ambient light sensing device of the presefit invention is to be used with a single ballast 2, and particularly when the ballast 2 doe~ not have a dimming control circuit 42, po-er/output terminal 420 will be connected to non-inverting input 17 (pin 2 of pulse width modulator 4), and the ground terminal 419 ~ill be connected to the ground of Figure 1, i.e. to the grounded side of variable resis~or 18 so that control lines 315 are connected across variable resistor 18. Thus, powerfoutput terminal 420 i8 connected in the Yoltage ; divider comprising resistor 16 and~variable resistor 18. The operation of ; processing cireuit 310 as described above ~ilI reduce the voltage at ~on-invert~ng input 17 ~n respo~se to an increase in estennally-provided light se~sed b~ photocell 3~8.
hen ballast 2;is provided with an electronic dimming circuit 42 as detailed~in F~gure~2, ;the~powertoutput termLnal 420 ~ill be connected to the compeDsation pîn (Pl)~of~frequency source 55 and the ground ~erminal ;419~ will~be~connected~to the~ground of the~circuit of Figure 2, i.e. to the gr~ou~ded~ side of ~ariable resistor 94. Thus, control lines 316 of ensing~and co~trol circuit 300 are connected across variable resistor 94.
~it~ ~his co~nection, the~pouer/output terminal 420 is connected to the i center of the voltage divider comprising resistor 96 and variable resistor : ` : : :
94. As noted previously~. the compensation pin (P13 of frequency source 65 controls the duty cycle of the pulse vidth~modulated output of electronic dimming circuit 42 vhich controls the brightness of the load 26. Thus, hen transistor 406 is turned on by ambient light i~pinging on photocell .
308, the voltage on the compensation pin ~ill be reduced and the pulse output of electronic dimming circuit 42 ~ill have a reduced dut~ cycle.
ID this vay, the circuit of the present invention produces further dLmming of he load 26 in response to an increase in ambient light. It is a w093~0964g 19 - 2 1 2 3 ~ 2 6 PCT/US92/0~46 particular advantage of this embodiment that the dimming produced in respo~se to eny increase in ambient light occurs ~ith reference to the dim~ing level set by the occupant of the area using variable reæistor 94.
Thus, any desired l$ght level can be produced, and the selected level will be approsimately maintained in spite of fluctuations in e~ternally available light such as sunlight.~
..
A particular advantage of sensing and control circuit 300 of the present invention is that this circuit can be used readily with one or ; many lighting fistures. In addition, sensing and control circuit 300 is useful both with fixtures; driven only by electronic ballasts 2, and also ith fixtures which further incorporate a lo~-voltage, pulse-witth odulated brightness conerol~circuit such a~ electronic dimming circuit 42.~
Electronic dimming circuit 4~ can be used to control a plurality of ballasts 2; therefore, if desired, a single sensing and control circuit 300 may be connected to sn~electronic dim~ing circuit 42 to control a plurality of~ballasts 2 to dim their loads 26 in response to an increase in~a~bient lighe. ~AlternaeiYely, the conerol lines 316 could be connected in parallel to a;~plurality~of electronic dimming circuits 42 (across variable~resistor 94~in~e-cb~Qs~ described previously). If a large number of~electronic dimming circuits 42 and/or ~allasts 2 are to be connected to ~single sensing~Rnd conerol~circuit 300, sensing and cantrol circuit 300 s~ould be provided wieh amplifying means.~such as a trensistor circuit, to incre~se~ies fanoue capQciey~ For eYample, an NPN po~er transistor can be used~eo~in~rease the f~anout capability~ of sensing and control circuit 300 by connecting its~base~eo~the~outpue, its collector to a DC power source suc'h~as~that provided~at Vcc~(pin 7) of ~frequency source 65, and connecting~its emltter~ to;~ehe eleceronlc dimming circuits 42 and/or b-llase6 2~t~o be conerolled ;thereby.~ Various technlques ~of increasing fanout capaciey of the~output are within the ability of those of ordinary i s~ilI in ehe art~ and wlll not be described further here. Thus, it can be sèen that the fanout~cQpablllty~can be eYpanded to alloY control of almost any~number of ballssts~ 2 andlor electronic~dimming circuies 42 using well-kno~n tec~niques. ~
The design of the~present invention therefore permits a single senslng~ and control~clrcuie~300 eo~be connected directly to the non-inverting inputs 17 of~Q plurality~of ballasts 2, or the terminals Pl of a plurality of electronlc~dimming circuits 42, to control a large number of lamps. The use of a single sensing and control ci~cuit 300 as described ~: :: :

W O 93JOg6~g PCTIUS92/09746 3 2 2 6 ~ ?S
herein is particularly desirable since this method reduees cost and e~hances rel~ability. In addition, a single sensing and control circuit 300 will provide more uniform control of lights in a given area such as in a ~ingle room. Because of ambisnt light variation ~ithin areas, and ; because of variations in calibration ~nd response betveen multiple sensing ~ and control circuits 300, lamps in the same area that are controlled by .
different sensing and co~trol circui~s 300 may e~hibit variation in light ~ output. This continual variation ~Ay be annoying to persons working in : the area. Thus, it is prefer`able to ~se a single sensing and control circuit 300 to control all the lamps in a lighting zone.
~:: Sensing and control circuit 300 is a low~Yoltage, low-power circuit : and connects only to the low-voltage, low power side of the integrated circuits uced in ballast 2 and electronic dimming circuit 42. Thus, ~ire~
: connecting sensing;and control circuit 300 to the various electronic dimming circuits 42 andlor ballasts 2 controlled by the sensing and , ~
control circuit 300 need not conform in size or routing to the code : require-ents that w~uld be applicable to wires needed to operate higher po~er and ~oltage circuits~. :
F:igure:5 :detail:s a preferred arrangement and construction of the components~shown in Figure 3. ~ This arrangement is particularly designed :or uee with fluoresc~ent:~li&hts~ installed in~ a typical office building gr~id and panel'~:ceilin&~syatem. ~As shovn, a fisture 501 co~prise~ the load~ 1uorescent~tube)~:26:and dim~ing ballast 2, located in fixture hou~s~i~n&~5~02. ~FiYture 5~01~ is suspended in ceiling grid 504. A
.s. ~ ;translucent~diffuse;r~506 covers the components ln fixture hou~ing 502.
'Geiling~panels:~:508::fill;the sections in:ceiling grid 504 ~hich do not contai~a~fi~ture~hougin&~502.:~Ballast~2 is~co~nected to and drives load 26~ Fi~ture~SOl will~generaLly contain th Ne or four similarly coDnected loads~:~Z6~,~ although~for~cla`rit~onl~ one load~26 i8 S~OW~ in Figure 5.
: Fi~ture hous:ing 502~ls con~entional in that it has one or more holes 510 ~itb removable knockout:~pl~gs. Such holes are generally provided in fixtures to accept~:cable: clamps and thus facilitate electrical po~er service~to fixture 501.
ousing 312 is preferably a small, round plastic housing ~ith a body 513 snd a threaded~portion~512 smaller t~a~ the body 513. Threaded portion~512 is installed:through hole:510:of fi~ture housing 502. ~ousing 312 is~held in place by a:~locking nut 514:of the t~pe normally used ~ith electrical cable clamps~ Prom the end of housing 312 oppos~ite threaded ~ . portion 512, a~ adjustment for potentiometer 416 pro~ects so that this :: :

WO ~3JOg64g PCI`/US92/~9746 . _ 21 ~ 21 23 22 6 adjustment is accessible without remo~ing or disturbing housing 312.
Potentiometer 416 may be of the type ~hich is adjustable using a screwdrl~er, a~d will then be installed 80 that the adjustment is acceæsible from outside housing 312. Also, fiber optic cable receptor 516 is provided on housing 312. Receptor 516 is a hollow tube of brass or other appropriate material, threaded on the outside, and having four slots cut i~ its e~t, transverse to the threads, at 90 degree intervals about it~ circumference. The very~end of receptor 516 has sn unthreaded portion ~hich is beveled on the outside surface so that the beveled surface forms a portion of a cone with its apex beyond the beveled end of receptor 516.
The hollo~ port on of receptor 516 recei~es the end of fi~er optic cable ;306, which slides in and is held in close proximity to photocell 308, ~hich is located~in housing 312 (as shown in Figure 3). The threads on receptor 516 receive brass loc~in~ nut 518, which, through tightening onto the beveled end of receptor 516, slightly compresses receptor 516 toward its central longitudinal a~is, thus tightenin~ the slotted portio~s thereof~against fiber optlc~cable 306. Thus, receptor 516 iæ a means for lockably connec~ng fiber optic cable 306 to the housing 312 in a fi~ed manner~ 80 that }ight~passing through fiber optic cable 3~6 shines on photocell 308. ~ ~
Fiber optic cable 306~is~preferably a stranded fiber optic cable with a plastic~ insulating jacket~520. Fiber optic cable 306 preferably has a total ~diemeter on~t~he o~rder of 0.125 inches, and ~ill be sized in conjunction with receptor~;516,~locking nut 518, and the components of housing~;304~`to permit~good mechanical -nd light transmission connections therebetween.
Housing~3~4 compris~es :;~threaded tube 522, locking nut 524, flst washers~S26 and~528,~nd~nuts~ 530 and 532. Threaded tube 522 ma~ he a brass tube, generally~imilar to the previously described receptor 516.
The tube 522 is hollo~throughout, and is threaded o~ the entire outside ~urface and on st 1east part of the Lnside surface to rece~ve pri~sm 302.
, The end o~ tube 522 pro~imate to the fiber~optic cable 306 is slotted and beveled as previously de~scribed with reference to the fiber optic cable end ~f receptor 516. Locki~g nut 524 is identical to lockLng ~ut 518 and, like loc~ing nut 518, serves as a me~ns to hold fiber op~ic cable 306 stationary relative to the associated fiber optic receiving tube. Of :: : : :, course, other types of compression fittings, su~ch as plumbing fittings, and various other types of clamping hardware~designs could also be used vithin the spirit of the invention.

W O 93/Og649 PCT~US92/0~746 2123226 22 ~ t Tube 522 is prefer~bly 1.75 inches long, although other lengths could ~e u~ed. ~hat i8 important is tha~ tube 522 be of suficient length to pass through the thickniess of ceiling panel 508 or other structural me~ber through ~hich installation i8 desired, leaving suifficient ~pace on the ends of tube 522 for connection of the necessary fittings. Specifically, vashers 526 and 528 and nuts 530 and 532 are tightened on the outside threads of tube 522 to hold housing 304 in place with respect to-ceiling panel 508. Washers 526 and 528 are preferably large plastic ~ashers formed in a color to match snd thus visually blend into the ceiling panel~
508.
Prism 302 is threaded into one end of the tube 522, and fiber optic oable 306 is inserted into the other end of tube 522 and clamped, using locking nut 524, in llght transferring relationship with prism 302, e.g.
so that the end of fiber optic: cable 306 abuts prism 302. Fiber optic cable 306 is prefera~ly of sufficient length to permit desired positioning of housing 304 relati~e to:the source of ambient light 314, while not gerlerating excessive cost or producing so much light loss due ~o its length that operation of the~circuit is adversely affected. In prac~ice, a length of about 22 i~ches has been found effective.
Figures 6a and 6b show t~e construction of prism 302 in greater detail. Prism 302 has a body 601 in the shape of a partially cut-out cy}inder. The ~on-cut-ou:t portion of body 601 defines a collec~ing surface~602,~2nd :the cut-~ut portion defInes a beveled re~lecting portion 606~. ~Figure 6a is a frontal vie~ of prism 302 particularly showing the eolleeting surface 602~of:prism 302. Flgure 6b is a corresponding side vie~ of~the same pr:ism, showing the shaping o~ the beveled, reflecting portion~606. To facilitate~light collectio~, beveled portion 606 ~as two substa~tially:flat:reflecting:~surfaces 6~8 and 610 which tend to reflect ght~approiching from~different angles upYard through threaded portion 604.: Preferably,: the angle~between collécting sur~ace ~02 and reflec~ing surface 608 is about 30 degrees, ~nd the angle bet~een collecting surface 602 and reflecting surface 610 is about 60 degrees. When prism 3~2 is installed very close to a ceiling, the ref}ecting surfaces 608 and 610 ill be especially effecti~e at gathering light reflected from the ceiling itself and also at gatherLng light comLng directly through a window. This precise light gathering;capability makes possible the use of the less complex circuits and simple algorithms of the preferred embodiment. Prism 302 is preferably made from clear Lucite or other appropriate formable, trsnslucent optical m&terial~

:~
: ::

W O 93fOg64g - 23 _ 2 1 2 ~ ~ 2 6 PCT/US92/097~6 Positioning of the reflecting prism 302 is important to ~ssure maYimum energy savi~gs and proper perfor~ance of the circuit. In general, the prism should be positioned with the collecting surface 602 facing the window or other ambient light source. The top of the t~threaded par~ of prism 302 should be installed as nearly flush vith the lo~er surf~ce of ceiling panel 508 as possible.
Prism 302 could also be installed to collect light from a region below the hou~ing 304, such as from a work surface. ~owever, such an arrangement is less preerred becaufie mo~ement in the area and variations in the reflectivity of surfaces will significantly affect the amount of light collected by the simple prism 302, causing undesired lighting efects. A more complex le~s, capable of gathering light from a wide area so as to average ~he light readings from the area I is required or do~nward monitoring to avoid abrupt shif~s in load brigh~ness due to movement in the area or placement of papers on a desk. A s~stem using down~ard light collection will generally produce more accurate cor.trol of load brigh~ncss, but significantly increases the cost and complexity of the system. Thus, the system design shown in Figure S is preferred over a do~n~ar~-aimed light ollection system because it provides acceptsble operation with m~nimum cost and compleYity.

: i ~;
:: : :
:

Claims (21)

I claim:

1. A lighting control system for gas discharging lamps, comprising:
a control circuit for controlling a power circuit wherein the power circuit supplies power variably to a gas discharge lamp load in response to the level of a low-power, variable DC control input voltage applied to a control input of the power circuit, said control circuit comprising control pulse generating means for generating control pulses of variable duty cycles; brightness control means connected to the control pulse generating means for setting the desired brightness of the load; and integrating means, connected between the power circuit control input and the control pulse generating means, for integrating the variabale-width control pulses of the control pulse generating means to produce the variable DC control input voltage to the control input of the power circuit;
an ambient light sensing circuit connected to the control pulse generating means for sensing the ambient light level and producing a variable control output depending on the ambient light level;
wherein the control pulse generating means varies the duty cycle of the control pulses with the control output of the ambient light sensing circuit such that the brightness of the gas discharge lamp load is decreased when the amount of available ambient light increases.

2. The system of claim 1 wherein the control output of a single said ambient light sensing circuit is connected to a plurality of said control circuits.

3. The system of claim 1 wherein the ambient light sensing circuit comprises: a lens adapted to collect light primarily from an ambient source other than said gas discharge lamp; a fiber optic cable connected to said lens and to a circuit housing for transmitting light from the lens to the housing; wherein the housing contains a photocell circuit comprising a photocell and a sensitivity adjustment potentiometer, with the photocell circuit producing the control output of the ambient light sensing circuit in response to light received by said lens.

4. The system of claim 1 wherein the brightness control means and the ambient light sensing circuit are both connected to a common input terminal of the control pulse generating means such that the brightness control means and the ambient light sensing circuit simultaneously affect the brightness of the gas discharge lamp load.

5. The system of claim 1 wherein said ambient light sensing means comprises delay means for preventing the ambient light sensing means from affecting the lamp brightness during a defined period immediately after activation of the lamp so that the lamp is started at full brightness.

6. A lighting control device for use with a lighting fixture including a lamp, comprising:
collecting means for collecting ambient light;
flexible cable means having first and second ends, the first end connected to the lens means is light transmission relationship for receiving and carrying the ambient light collected by the lens means;
photocell circuit means connected to the second end of the flexible cable means and adapted to be connected to a dimming circuit of the lighting fixture the dimming circuit variably controlling the brightness of the lamp, said photocell; circuit means adapted to receive the ambient light, generate a variable dimming control signal varying with the amount of ambient light available, and transmit said dimming control signal to s-id lighting fixture dimming circuit to effect reduction of said lamp rightness is response to an increase in available ambient light.

7. The device of claim 6 wherein said collecting means is adapted for installation in a ceiling proximate to the lighting fixture.

8. The device of claim 7 wherein said collecting means includes locking means for fixing the lens means in an installation hole formed in a grid-type ceiling panel.

9. The device of claim 8, wherein said collecting means is adapted to collect light primarily from one direction.

10. The device of claim 9 wherein the collecting means comprises a prismatic lens having a directional receiving surface and at least one reflective surface for reflecting ambient light received through the receiving surface into the first end of the flexible cable means.

11. The device of claim 9 wherein the prismatic lens has at least two reflective surfaces, one at about 30 degrees angle with respect to the receiving surface and the other at about a 60 degree angle with respect to the receiving surface.

12. The device of claim 8, wherein the collecting means comprises a threaded tube with two ends which receive an ambient light-collecting lens at one end of the tube, with the first end of the flexible cable means inserted into the other end of the tube.

13. The device of claim 12 wherein said locking means include nuts threaded onto the outside of said tube to hold the tube in a hole provided therefor.

14. The device of claim 12 wherein the ambient light-collecting lens is threaded for installation into the one end of the tube.

15. The device of claim 12 further including cable locking means for holding the flexible cable means in a fixed position relative to the tube.

16. The device of claim 15 wherein the one end of the tube is compressible and said cable locking means comprises a compression nut for compressing the one end of the tube onto the flexible cable means.

17. The device of claim 7 wherein said photocell circuit means is contained in a housing adapted for connection to the lighting fixture through a standard knockout plug.

18. The device of claim 7 wherein said housing comprises a housing tube for receiving the second end of the flexible cable means and holding said second end in light transmission relationship with the photocell circuit means.

19. The device of claim 18 further including cable locking means for holding the flexible cable means in a fixed position relative to the housing tube.

20. The device of claim 15 wherein one end of the housing tube is compressible and said cable locking means comprises a compression nut for compressing the one end of the tube onto the flexible cable means.

21. The device of claim 17 wherein said photocell circuit means further includes delay means for preventing the photocell circuit means from affecting the lamp brightness during a defined period immediately after activation of the lamp so that the lamp is started at full brightness.