US3169213A

US3169213A - Fluorescent lighting method and means

Info

Publication number: US3169213A
Authority: US
Inventors: Shaheen John
Original assignee: Individual
Current assignee: Individual
Priority date: 1962-07-19
Filing date: 1962-07-19
Publication date: 1965-02-09
Anticipated expiration: 1982-02-09

Description

Feb. 9, 1965 SHAHEEN 3,169,213

FLUORESCENT LIGHTING METHOD AND MEANS Filed July 19. 1962 INVENTOR.

JOHN SHAHEEN ATTORNEYS United States Patent Ofiflce 3,169,213 Fatented Feb. 9, 1965 This invention relates to fluorescent lighting and more particularly to method and means for operating a plurality of fluorescent or are dischargelarnps out of phase with each other and in such a way as'to substantially eliminate stroboscopic effect or flicker.

The aforementioned flicker is present to a greater or lesser degree in all are discharge lamps and occurs when the current through the lamp supplying the excitation energy to the phosphor coating on the lamp fluctuates and drops to Zero twice during each cycle of the alternating current generating source.

Efforts have been made to solve the problem of flicker by groupinga plurality of lamps together as a unit and operating them out of phase with each other so that the intervals of reduced light intensity occur at different times for each lamp with the result that there tends to be a more uniform light emanating from-the three lamp unit. In large buildings the phase differences between the several lamps of the unit are most commonly obtained by connecting each lamp of the lamp unit between different phases of a polyphase power source. phase power that is distributed locally to the panel boards of commercial buildings is 208 volts and derives from a three phase Y. connected source having 120 between each phase and a grounded neutral, the light units consisted usually of three similar lamps all mounted in a single fixture and connected respectively through three similar transformers in star or delta to the three phases of the polyphase source delivering to the panel board. While this means for obtaining strobe correction has been satisfactory up to a point, particularly when lampshaving highly retentivephosphor coatings areused,there still remains a substantial flicker which though not consciously apparent to the observer,'is detectable by a photocell and does cause substantialstrainrand discomfort to the eyes. This subliminal flicker is particularly distressing to persons using their eyes constantly and for long'periods of time under such light as, for example, while readingin a library or assembling small parts in a factory. I,

The aforementioned difficulty isbelieved to beduejto the fact that although the potentials supplied to the three lamps'of the prior lighting units are 120 out [of phase with each other so that their voltage waveformsoverlap,

'there are still intervals of reduced voltage (and) current) Since most polyand across which the prior devices have been connected, it is found that the third, ninth, fifteenth, etc. harmonics cancel out and do not contribute to the line voltages. Resultantly, there is a more pronounced peak at the points in each cycle where the voltage reaches its maximum and minimum and also a less rapid rate of change of voltage with time in the regions where the voltage approaches zero.

and Where the fundamental is not reinforced by the above odd harmonics, particularlyrthe third harmonic; When the several line voltages of the three phase source are observedtogether on an oscilloscope, there is still seen to be a pronounced fluctuation in the envelope enclosing the three line voltages and which is believed to account at least partially for the aforementioned subliminal flicker. The priorstrobe corrected lighting apparatus of the type here concerned are disadvantaged also because they require at least three electrical leads from the three phase source to the light fixture. three phase power may be available or brought to a panel board in an existing building, usually the building itself is not wired for three phase (3 or 4 wire) distribution. Only two wires are available between the panel board and the individual electrical fixtures or outlets. Consequently, a third wire must be run throughoutthe building before these prior devices can be installed. This, of course, increases substantially the installation costs of and reduces the desirability as original or replacement equipment of the prior lighting apparatus. I have improved the art of fluorescent lighting by pro-. viding a simple lighting apparatus for mounting in a single fixture and which-costs no more than prior comparable devices but which provides illumination of substantially uniform intensity and with substantially 'no subliminal stroboscopic effect or flicker. Under my invention, .both

the coil voltages and the line voltages of the three phase;

Y connected source are used. These non-sinusoidalvolt ages are applied to the several lamps of the unit and mm-.,

bine in phase relation and overlap in such away as when observed together to produce a more uniform voltage envelope and a more uniform illumination from thelightingunit. i 7 Further, the lighting apparatus of'this invention can be installed readily in existing buildings because it d oes not require athird wireto be run from the. panel board or other three phase source to the fixture. This is because, in practice and as mentioned "previously, all low or fluctuations in the voltage envelope, between' adjacent voltage maxima and minima during each cycle ofoperation. Consequently, there are also intervals wherein reduced excitation'energy is supplied to the phosphorjcoating of and resulting in intervals of reduced light intensity from one or more of the lamps of the unit. I

' As mentioned previously, prior strobe corrected fluorescent lighting apparatus have been connected in star or delta to the several phases or in other words to obtain the line voltages from a grounded three phase Y connected source found locally. Thislocal powerultimatelyderives from a threephase generating device which, inpractice, is not an ideal alternator andwhich generatesin ,each of its windings a coil voltage which is not sinusoidal but which is rather the sum of a fundamental waveplus the odd harmonics. The' resulting coil voltage waveforms have maxima and minima which are flattened andfmade wider and the rate of change of voltage with time is substantially increased in the regions Where the voltages approach zero. On theothenhani when calculating the line voltages or voltages between the phases generated by such "a source, I

lamps 14, '15. I 5 H p Y Under my invention, a third autotransformer 16 is;

voltage (under 300 v.) three pliase'Y connected distribution circuits are required to be grounded at the pole; Thus ground can function'eifectively'as the third conductorbetween, my lighting unit and the power source. Accordingly, to. effect strobe correction, the circuit ofmyap paratus may simply be connected to the conventionally grounded light fixture or junction boxinwhich "the unit itself ismounted. 7 1 1 In the illustrated embodiment: j I p j The figure of the drawing is a diagramaflerepresenta tion of my improved strobe corrected threelarnp lighting unit connected at a panel board to two: phases ofa grounded three phase Y connected generating source." 1

Referring to the drawing, my improved lighting appanatus comprises a pair of similar autotransf or'mers'm,

11 having their low voltage terminals 12,13 respectively connected together and to the low potential ends of 'afpair of conventional single phase self-starting fluorescent lamps 14, 15 which may be type 96Tl2, for example, requiring fortheir operation a potential of approximately 630- volts. Transformers 10, "ll have also high voltage rer: minals 6, 7 connected respectively through; inductive the high tentiaI eridSf or elements or chokes 8, 9 to More particularly, although provided also which is different from the aforementioned transformers if), 11 :as will hereinafter be described more particularly. Autotransformer 16 has its low voltage terminal 18 connected to the intermediate voltage terminal 19 of autotransformer it and its intermediate voltage terminal 20 connected to the intermediate voltage terminal 21 of autotransformer 11. A third fluorescent lamp 22 similar to lamps 14, 15 is connected across the full winding of autotransforrner 16 and has its low potential end connected to the low voltage terminal 18 and its high potential end connected through inductive element or choke 23 to the high voltage terminal 24 of autotransformer 16. Thus the primaries of transformers 1f 11 are connected together in series and the series combination is connected in parallel with the primary of autotransformer 16.

A conductor id is provided for connecting the inte mediate voltage terminal 19 of autotransformer to panel board 26 and more particularly to the panel board terminal indicated at A delivering one phase, say phase A of a three phase Y connected alternating potential source 29. Also a conductor 27 is provided for connecting the intermediate voltage terminal 21 of transformer 11 to the panel board terminal indicated at B delivering another phase, sa'y phase B, of said alternating potential source 29. It will be understood, however, that the conductors '25, 27 can just as well be connected to phase A and phase C (indicated at C on the panel board) respectively or indeed to any two different phases of the alternating potential source 29.

A third conductor 28 may be connected between the low voltage side of autot'ransformers 10, 11, say at 13, to the panel board 26 and more particularly to the neutral terminal indicated at N therein, which terminal is, as mentioned previously, always grounded in' low. voltage distribution circuits. or more preferably and if as usual the electrical outlet in which the lamp unit is to be mounted isgrounded, the circuit at point 13 may simply be grounded to that outlet.

In the usual commercial balanced three phase generator, three equal coil voltages, that is voltages between the phases and the neutral are produced across the several Y connected coils and these voltages are, 120 out of phase with each other. The coil voltages add vector ially to produce three equal line voltages, that is voltages between the several phases, which are also 120 out of phase with each other and advanced 30 with respect to the aforementioned coil voltages. And for these balanced three phase generating sources, the linevoltage is found to be V? times the coil voltage. The aforementioned relationships pertain also to the three phase power distributed locally to the panel board 26, and in practice the potential between phases A, B or C and N is approximately 120 volts while the potential between any two of phases A, B, C is approximately 208 volts.

It is a feature of this invention that my lighting apparatus utilizes both line and coil voltages to power the several lamps of the unit for more effective strobe correction. More particularly, two of the three similar lamps of the unit, namely lamps 14, are connected through their respective similar autotransforme'rs 10, 11 across the panel board terminals A, N and B, N respectively. The potentials across the lamps, therefore, derive ultimately from two different coil voltages produced in the generating source 29 and are equal in magnitude and 120 out of phase with each other. Also as mentioned previously, the coil voltages are non-sinusoidal and contain in addition to the fundamental, the odd harmonics particularly the third which tends to oppose the fundamental at its maximum and minimum points and to reinforce the fundamental at the points where that approaches zero amplitude thereby producing voltage waveforms having flattened maxima and minima and short intervals of reduced voltage at alternation.

Further in accordance with the invention, the third lamp 22 provided in each unit is connected through its transformer 16 across the panel board terminals A, B. The third lamp is thus powered by the line voltage between phase A and phase B of the generating source 29 which voltage is out of phase with and exceeds by a factor of V? the aforementioned voltage between terminals A, N and B, N. Also it contains no tn'plen (third, ninth, fifteenth, etc.) harmonics for reinforcing the fundamental at the points where that approaches zero amplitude and for opposing the fundamental at its maxima and minima. To accommodate the voltage differences and in order to provide the same potential across each of the similar lamps 14, 15, 22, the transformation ratio of autotransformer 16 is made approximately times the transformation ratios of autotrans'formers 10, 11. For the usual commercially distributed power, then, autotnansformers 1f 11 may be standard volt ballast transformers while autotransformer 16 may be a 208 volt transformer.

Thus when my lighting apparatus is connected as above, the potentials across the three lamps l4, 15, 22 are out of phase with each other and equal in amplitude. But the potentials across lamps 14, 15 only are altered as described particularly by the third harmonic, while that across tube 22 is not affected by said third and the other triplen harmonics. With the aforementioned differences in the shapes of and the phase relations between the several voltages powering the several lamps of the unit, these voltage waveforms when observed together are found to be contained in a more uniform voltage envelope and there is produced in the three lamp unit a light of uniform intensity and with substantially no stroboscopic effect or flicker.

Further, the three lamp lighting unit of this invention requires in the usual situation only two wires fr'omthe unit to the panel board. That is, if as usual the junction box or outlet in which the unit is installed is already grounded, the third electrical lead 28 may be eliminated and the circuit grounded at 13 to the fixture. Thus the instant apparatus may be installed readily and inexpensively and with no additional wiring as replacement equipment in existing building outlets. For a nearly balanced power factor for most efficient operation of the overall installation, the three lamp units of this invention are desirably installed in groups of three, with each unit being connected to different phases at the panel board 26. Thus the first unit is connected to terminals A, B, the second unit to terminals B, C and the third unit to terminals C, A. And of course, more than one unit may be connected in the several groups.

I claim as my invention:

1. Lighting apparatus comprising: first, second, and third transformers; corresponding first, second, and third are discharge lamps connected across the secondaries of said transformers; a generator having Y connected coils; electrical connections between the primary windings of said first and second transformers at one terminal thereof and the common terminal of said coils; electrical connections between the primary windings of said first and second transformers at the other terminals thereof and the other terminal respectively of first and second ones of said coils, and electrical connections connecting the primary of saidthird' transformer across said first and second ones of said coils.

2. Lighting apparatus comprising: three transformers; three similar arc discharge lamps; means for electrically connecting the secondaries of said transformers respectively to said lamps, the primaries of two of said transformers being connected together in series, the primary of the other of .said transformers being connected in 3. Lighting apparatus for mounting in a single fixture comprising: three autotransformers; three corresponding similar are discharge lamps; eiectrical connections between ea'ch of said lamps at one end thereof and the high voltage terminal of its corresponding autotransformer; electrical connections between each of said lamps at the other end thereof and the low voltage terminal of its corresponding autotransformer, two of said autotransf ormers having substantially equal voltage transformation ratios, said ratios being approximately equal to /3 times the transformation ratio of the other of said autotransformers; an electrical connection between the low voltage terminals of said two of said autotransformers; and means for connecting the intermediate voltage terminals of said two of said vantotransformers respectively'to the low voltage and the intermediate voltage terminals of the other of saidautotransforrners.

4. Lighting apparatus for mounting in a single fixture comprising: three autotransformers; three corresponding similar arc discharge lamps, each ofsaid lamps being connected at one terminal thereof through a reactive element to the high voltage terminal of its corresponding autotransformer, each of said lamps being'connected also at the other terminal thereof to the low voltage terminal of itscorresponding autotransformer, two of said autotransformers having substantially equal voltage transformation ratios, said ratios being approximately equal to /3 times the voltage transformation ratio of the third of said autotranstormers; means for connecting the low voltage terminals of said two of said autotran-sformers to each other and means for connecting the intermediate voltage terminals of said two of said autotransformers respectively to the low voltage terminal of the third of v terminalfofvsaid third of said autotransformers.

5'. Lighting apparatus for mounting in a single fixture comprising: three autotransforrners, two ofsaid autotransformers having substantially equal voltage 'trans- 0 formation ratios, said ratios being approximately equal lto 3 times the voltage transformation ratio of the third of said autotransformers; three corresponding similar arc discharge lamps connected across the full windings of said autotransformers; electrical connections between the low voltage terminals of two of said autotransformers and ground and electrical connections between the intermediate voltage terminals of said two of said autotransformers and the primary of said third of said autotranoformers. r V

6. A lighting system comprising a plurality of lighting units, each of said units containing three transformers, two of said transformers having their primaries connected together in series and having, substantially equal voltage transformation ratios, the third of said transformers having its primary connected in parallel with the primaries of said two'of said transformers and having a voltage I transformation ratio equalrto substantially the 7 r times said ratios of said two of said transformers.

References Cited by the Examiner I UNITEDSTATES PATENTS 2,683,798 7/54 Craig 315-144 X 2,996,644 8/61 Nathanson 315-438 3,027,490 3/62 Craig 315-144 3,032,682 5/62 Lord 315--144 DAVID J. GALVIN, Primary Examiner.

JAMES D. KALLAM, Examiner.

Claims

1. LIGHTING APPARATUS COMPRISING: FIRST, SECOND, AND THIRD TRANSFORMERS; CORRESPONDING FIRST, SECOND, AND THIRD ARC DISCHARGE LAMPS CONNECTED ACROSS THE SECONDARIES OF SAID TRANSFORMERS; A GENERATOR HAVING Y CONNECTED COILS; ELECTRICAL CONNECTIONS BETWEEN THE PRIMARY WINDINGS OF SAID FIRST AND SECOND TRANSFORMERS AT ONE TERMINAL THEREOF AND THE CONNON TERMINAL OF SAID COILS; ELECTRICAL CONNECTIONS BETWEEN THE PRIMARY WINDINGS OF SAID FIRST AND SECOND TRANSFORMERS AT THE OTHER TERMINALS THEREOF AND THE OTHER TERMINAL RESPECTIVELY OF FIRST AND SECOND ONES