US2177488A - Illumination intensity control system - Google Patents

Description

Oct. 24, 1939. R. B. HUNTER 2,177,488

ILLUMINATION INTENSITY CONTROL SYSTEM Filed Feb. 5, 1936 2 Sheets-Sheet 1 /WWAX Ex 3. NO I\ V g; vMfl Qs- I Oct. 24, 1939. R. B. HUNTER ILLUMINATION INTENSITY CONTROL SYSTEM Filed Feb. 5, 1956 2 Sheets-Sheet 2 Patented Oct. 24, 1939 I UNITED STATES PATENT OFFICE SYSTE Richard B. Hunter, Shorewood, Wis., assignor to Cutlenflammer, Inc., Milwaukee, Wis., a corporation of Delaware Application February 5, 1936, Serial No. 62,459

12 Claims.

This invention relates to electric illumination intensity control systems and more particularly to systems and apparatus for controlling the degree of energization in lighting circuits employed for outdoor and indoor ornamental and display lighting.

An object of the invention is to provide a novel illumination intensity control system wherein a multiplicity of intensities of illumination for a group of lamps may be preselected and wherein means are provided for effecting gradual transition from one preselected intensity of illumination to another in uniform increments and decrements substantially proportional to the difference in said preselected intensities.

Another object is to provide a system of the aforementioned character wherein novel means are provided for effecting a continuous cycle of variations in the intensities of illumination of go the group of lamps in accordance with the values of intensity preselected therefor.

Another object is to provide a system of the aforementioned character wherein means are provided for simultaneously effecting the 25 changes in illumination intensities of a plurality of groups of lamps in accordance with the values of intensity preselected for the respective groups.

Another object is to provide a novel arrangement of the control parts of the system where- 30 by the degrees and rates of change of the illumination intensities of the respective groups of lamps may be visually indicated in advance.

Various other objects and advantages of the invention will hereinafter appear.

The accompanying drawings illustrate certain embodiments of the invention which will now'be described, it being understood that the invention is susceptible of embodiment in other forms without departing from the scope of the appended claims.

In the drawings,

Figure 1 illustrates schematically and diagrammatically an illumination intensity control system embodying my invention.

Fig. 2 is a similar view of a modified form oi illumination intensity control system.

Fig. 3 is a plan view of a control panel which may be embodied in each of the systems illusm trated in the drawings,-one form of gag plate which may be employed in conjunction with the control elements of the device being shown in position on the control panel.

Fig. 4 is a diagram which shows by means of 3 curves the characteristics of illumination intensity control which are obtained with the systems illustrated in Figs. 1 and 2.

Referring first to Fig. 1 of the drawings,-I have illustrated, by way of example, three groups of electric lamps, continuity of circuit and in- 5 tensity of illumination of the lamps in the respective groups being subject to control by a system constructed in accordance with my invention; it being understood that in practice a larger number of lamp groups will ordinarily be 10 employed,the control elements being merely duplicated for each additional group of lamps. The three groups of lamps are designated in general by the reference characters I, 2 and 3. It is to be understood, of course, that any desired 15 number of lamps may be embodied in each group.

The groups of lamps l, 2, 3 are adapted to be connected across and supplied with current from the direct current supply lines designated as L L The supply of current to the lamps is controlled by suitable controlling devices, such as the dimmer rheostats designated respectively by the numerals 4, 5 and 5.

Assuming energization of the groups of lamps, the intensity of illumination of the lamps in each group is dependent upon the respective positions of the adjustable contact arms I, 8 and 9 of the dimmer rheostats, said contact arms to be hereinafter referred to as dimmer arms. Each of said dimmer arms I, 8 and 9 is shown in a position corresponding to the respective positions of the manually adjustable contact arms I, H and II, which are associated respectively with the sending rheostats I3, l4 and I5, said last mentioned contact arms to be hereinafter referred to as sender arms. Thus dimmer arm I is shown in mid-position to provide, say, half-bright illumination intensity of the lamps of group I, dimmer arm 8 is shown in its upper extreme position to provide full-bright illumination intensity of the lamps of group 2, and dimmer arm 9 is shown in its lower extreme position to provide for substantially black-out condition of the lamps in group 3.

Means are associated with each group of lamps to provide for movement or adjustment of the dimmer arms 1, 8 and 9 automatically from any given position or positions thereof to any other position or positions,-the position or positions to be assumed by each of said dimmer arms being initially preselected individually, as by the aforementioned sender arms In, II and 12. These positions may be preselected during rehearsal to provide the desired illumination effect of certain or all of the groups of lamps I Jointly,--whereupon the adjustments so eifected may be definitely registered upon a suitable gag plate or the like to provide for subsequent enactment of the exact illumination effect so preselected.

As shown in connection with the lamp group I the means for preselecting the positions and for controlling movement of dimmer arm 1 comprises essentially the aforementioned sending rheostat I3 with its associated sender arm i8, and in addition, the sending rheostats l6, l1, senderarms l8, l3 associated with said rheostats respectively, a receiving rheostat 20, an adjustable contact arm 2| to cooperate therewith,-- said arm to be hereinafter referred to as receiver arm,and the coil 22 of a polarized relay of known form,--said receiving rhe'ostat 20 and polarized relay coil 22 being connected with respect to each other and with respect to linesL L and selectively connectable with respect to sending rheostats I 3, l6 and Him the form of a Wheatstone bridge. It is understood that a considerably larger number of sending rheostats may be employed in practice.

A resistance, connected in an electrically closed loop, is divided into three sections 23, 24, 25, said sections corresponding in number to the number of sending rheostats. Said fader resist-- ance sections 23, 24, 25 are adapted to be introduced into said Wheatstone bridge circuit by an adjustable contact arm 26, said arm to be hereinafter referred to as fader arm,--to modify the controlling efiect of said sending rheostats in a manner which will hereinafter be more fully described. It will be understood that the number of fader resistance sections required corresponds in all cases to the number of sending rheostats employed.

The contactor 21 of the polarized relay is normally biased to an intermediate or neutral position, as illustrated, when the bridge circuit is in balanced condition, and the same is moved automatically into engagement with the stationary contacts 28, 29 selectively,,depending upon the sense in which the bridge circuit is unbalanced. Engagement of stationary contact 28 by contactor 21 eiiects energization of a switch 30, response of which connects field winding F of a split-field reversible motor M across lines L L to effect operation of said motor in one direction, whereas engagement of stationary contact 29 by said contactor effects response of a'switch 3| to energize said motor through its other field winding F to efiect operation of said motor in the opposite direction.

The means for preselecting the positions and for controlling the movement of dimmer arm 8 comprises a Wheatstone bridge circuit including sending rheostats I4, 32, 33 and their associated sender arms ll, 34, 35, respectively, receiving rheostat 36 and its associated receiver arm 31, a polarized relay having a coil 38, contactor 39, and stationary contacts 40, 4|, and fader resistors 42, 43, 44 and otheir associated fader arm receiver arms 31, 51 comprises the motors M M,

der ineffective their associated control apparatus.

The sender arms associated with the respective groups of sending rheostats are connected between the fader resistance sections comprising the aforementioned closed loops,-sender arm l0 being connected between fader resistors 23, 25, arm i8 being connected between resistors 23, 24, and arm I3 being connected between resistors 24, 25. Sender arms ll, 34, 35 and I2, 54, 55 are similarly connected with respect to fader resistors 42, 43, 44 and 62, 63, 64 respectively.

The fader arms 26, 45, 65 associated respectively with each of the sets of fader resistors, are adapted to be moved simultaneously and in like directions over said resistors by a pilot motor 14 through the medium of suitable reduction gearing, designated by the reference numeral 15, and a drive shaft 16. Said shaft 16 carries the gear wheels 11, 18, 19, which are in driving engagement with the gear wheels 88, 8|, 82, respectively, said last mentioned gear wheels carrying the respective fader arms 26, 45, 65. Movement of said fader arms effects variation ofthe in-- tensity of illumination of the groups of lamps in a smooth, gradual manner from one preselected value to the next, said values being in accordance with the setting of the sender arms. The resistance of the fader resistors, the resistance of the sending rheostats and the receiving rheostat and the resistance of the polarized relay coil in each control circuit are so proportioned with respect to each other as to afford a substantially straight line transition from one preselected intensity of illumination to the next.

For example, assuming the potential across lines L and L to be 120 volts, and the resistance values of thesending and receiving rheostats and the polarized relay coil each to be 1200 ohms, it has been found that the aforedescribed results are obtained by using a fader resistor whose respective sections have resistance values of 3000 ohms. Depending upon the degree of sensitivity of the polarized relay, the relatively higher ohmic value of the individual fader resistor sections obviously may be greater or less than the value' aforementioned as compared with the values of the sending and receivingrheostats.

Further details of construction of my illumination control system and one method of operating the same will now be described, chiefly in connection with lamp group I. Closure of switch 10 energizes lamp group I and its associated con-- ,trol circuit. Assuming the various control elements to be in the positions illustrated, the intensity of illumination of lamp group i will be- 4 at half-bright. Closure of the pushbutton switch 83 effects operation of the pilot motor 14- to effect simultaneous movement of the fader arms 26, 45. in a clockwise direction, for instance. Immediately upon inclusion of a portion of fader resistor 23 the Wheatstone bridge circuit becomes unbalanced in a direction to effect engagement by the polarized relay contactor 21 of the stationary contact 28, for instance, to energize the winding of switch 30. Switch 30 responds to energize motor M through its field winding F for operation in a direction to eifect downward movement of receiver arm 2i and dimmer arm 1 through the medium of suitable gearing indicated at 84. Said receiver arm and said dimmer arm are shown as being mechanically connected with but electrically insulated from each other.

As the fader arm 26 continues its movement over the fader resistor 23 the Wheatstone bridge circuit continues to remain unbalanced, the polarized relay effecting control of motor M for effecting gradual downward movement of dimmer arm I and receiver arm 2|, movement of the latter tending to restore the bridge circuit to balanced condition.

The motors M, M, W and the pilot motor 14 should preferably be so arranged that the rate of movement of the' dimmer arms is somewhat greater than that of the fader arms, so that there is virtually no lag in the movement of the dimmer arm with respect to the movement of the fader arm. I prefer to include an adjustable resistance 35 in circuit with the pilot motor I4 to provide for insuring the desired speed relation between the fader. arms and the dimmer arms. Obviously speed control for the motors M, M M may be provided, but this has been omitted from the disclosure to simplify the same.

When the fader arm 26 reaches the point between fader resistors 23 and 24 the sender arm I8 becomes wholly effective and the dimmer arm I substantially simultaneously reaches its lower extreme position, corresponding to the position of said sender arm I8. The lamps of group I will then be in substantially black out condition.

As the fader arm 26 continues to move it traverses the fader resistor 24 which is connected between the sender arms I8 and I9. Upon inclusion of a portion of said fader resistor 24 the Wheatstone bridge circuit becomes unbalanced in a direction to effect engagement by the polarized relay contactor 21 of the stationary contact 29; whereupon switch 3I responds to energize the motor M through its field winding F for operation in a direction to effect upward movement of receiver arm 2| and dimmer arm I.

When the fader arm 26 reaches the point between fader resistors 24 and 25 the sender arm I9 becomes wholly effective, and substantially simultaneously the dimmer arm 1 reaches its upper extreme position. The lamps of group I will then be at full-bright illumination intensity, the circuit thereof being obvious.

Continued movement of the fader arm 26 will effect unbalancing of the Wheatstone bridge circuit to effect downward movement of the dimmer arm I to a position corresponding to the position of the sender arm I to again provide half-bright illumination intensity of the lamps of group I.

It will be apparent that the aforedescribed cycle of operation will be repeated continuously as long as the pilot motor I4 is in operation.

Assuming closure of switches II, I2, illumination intensity variations will take place in the lamps of groups 2, 3 simultaneously with the illumination intensity variations being effected in the lamps of group I. Thus, as aforedescribed, the illustrated position of dimmer arm 3 provides for full-bright illumination intensity of the lamps in group 2, said dimmer arm being adapted to be moved from said position in the manner described in connection with dimmer arm I to positions which provide for variation of the illumination intensity from full-bright to half-bright, from half-bright to black-out and then back to full-bright, in accordance with the preselected positions of sender arms II, 34, 35, respectively.

The illustrated position of dimmer arm 9, as aforedescribed, provides for substantially blackout condition of the lamps of group 3, and said dimmer arm is adapted to be moved from said position to positions which provide for variation of the illumination intensity of said lamps from black-out to one-quarter bright, from one-quarter bright to three-quarters bright and then back to black-out, in accordance with the preselected positions of sender arms I2, 54, 55, respectively.

The aforedescribed cycles of variation in the intensity of illumination of the groups of lamps I, 2, 3 are represented by the curves shown in the diagram, Fig. 4. The solid line represents the illumination intensity characteristic of the lamps of group I; the dotted line and the dot and dash line represent the illumination intensity characteristics of the lamps of groups 2 and 3, respectively. The small circles in the respective curves represent the preselected intensities of illumination as determined by the positions of the sender arms. Thus circles A represent the intensities preselected respectively, by sender arms I9, I 0, I8; circles B represent the respective intensities preselected by sender arms 35, II, 34; and circles C represent the respective intensities preselected by sender arms 55, I2, 54.

It will be obvious to those skilled in the art that a system of the character aforedescribed aiiords extreme flexibility in the character of illumination intensity control of the various lamp groups, it being obvious that all or any portion of the complete range of adjustment of the illumination intensity of each group of lamps may be utilized by the individual sender arms associated therewith, and that regardless of the portion of the complete range of adjustment of the illumination intensity utilized for any other group or groups of lamps. Also it will be apparent that the system provides for decreasing or increasing the intensity of illumination of one or more of the groups of lamps during the increasing or decreasing of the intensity of illumination of other of said groups of lamps.

Fig. 2 illustrates an embodiment of the invention wherein the illumination intensity of the lamps in each of the groups I, 2 and 3 is regulated through the medium of a variable inductance device. The variable inductance device is provided with an exciting winding, and as is well known, variations of the current in such winding produce variations in the voltage drop in the inductance device and thus variations of the lamp voltage. The current in the exciting winding is controlled by means of an electron tube whose impedance may be varied by impressing upon a control grid of such tube a voltage which is the resultant of a variable control voltage and a voltage which depends upon and varies in accordance with the lamp voltage. Thus, regardless of the value of the lamp load, the voltage across the lamps and hence the illumination intensity of the lamps will be substantially the same for a given control voltage.

Referring to Fig. 2, L and L are the terminals of an alternating current constant potential source of supply. The elements in this embodiment of the invention which correspond to the elements in the embodiment of Fig. 1 are designated by corresponding reference numerals. Thus I, 2 and 3 indicate the groups of lamps, the voltage of which is to be regulated. The lamps of group I are connected in series with the coils IUI of a variable reactor I04 and across the lines L and L Said reactor I04 has an exciting winding II" which is connected in series with the electron tube IIIl across the lines L and L".

Electron tube H has a cathode III which may be heated in any well known manner, an anode H2 and a control electrode or grid, H3. Connected in parallel with the winding I0I isa halfwave rectifier H4, the purpose of which is to smooth out in a well known manner the ripples of the current in the winding I0'I as supplied through the electron tube H0.

A transformer H5 has a primary winding H6 connected in parallel with the lamps I, while one terminal of its secondary winding II! is connected to the control grid H3 and the other terminal is connected to a half wave rectifier H8. An energy storage discharge circuit, consisting of a condenser H9 and a resistor I20 connected in parallel with said condenser, is connected at one nected to cathode I H and to one end of a second 7 energy storage discharge circuit consisting of a condenser I25 and a resistor I26 connected in parallel therewith, the other end of said last mentioned energy storage discharge circuit being connected between the rectifier I24 and said firsti mentioned energy storage discharge circuit The sending rheostats I3, I6, II are connected at in parallel across the lines L and L and the fader resistors 23, 24, 25 are connected with respect to said rheostats as described in connection with Fig. l. The sender and fader arms in Fig. 2 are shown :1 positions corresponding to those shown in Fig. 1 and may be assumed to provide for similar results in the control of the illumination intensity of the lamps in the respective groups.

The system operates in the following mannerz-Current flows between the lines L and L through the coils IOI of the reactor I04 and the lamps I. The voltage drop through the coils IOI varies in accordance with the energization of the coil I01 in a well known manner. The current in the coil I0 'I is controlled by controlling the instantaneous voltage of the grid H3 during the positive half cycle, during which the tube I I0 permits current flow therethrough, provided that the voltage of the grid H3 is more positive than the critical voltage thereof. It will be noted that the voltage of the grid H3 with respect to the cathode III at any moment is the resultant of the instantaneous voltage of the condenser II 9 and the condenser I25,the two being connected in series. The condenser H9 is charged by a voltage impressed upon it by the secondary winding II! of the transformer H5 through the rectifier H8, said voltage being proportional to the lamp voltage. The rate of discharge of the condenser H9 is determined by the value of the resistance I20.

A voltage is impressed upon the condenser I25 through the secondary winding I23 of the transformer I2I, this voltage being a function of the adjustment of the sending rheostats I3, I6, I! and of the fader resistors 23, 24, 25, depending upon which of the rheostats and resistors is rendered effective by the fader arm 26.

In normal operation the fader arm 26 is moved gradually over'the fader resistors 23, 24, 25, and as it moves from its illustrated position it causes a diiference between the voltage of the condenser H9 and the voltage of the condenser I25, the

voltage of the latter corresponding at the first moment of change to the initial voltage of the lamps. Thus the resultant voltage from the two discharge circuits which is impressed upon the grid H3 is varied, causing a change in the current impressed upon the coil I01 and thusa change in the voltage supplied to the lamps. As the lamp voltage approaches the new value the voltage impressed on the condenser H9 varies due to the influence of the transformer H5 until when the new lamp voltage is attained the voltage of the two discharge circuits balance to a value at which no further change takes place in the current flowing through the tube I I0 and the winding I01. Obviously, as long as the fader arm 26 continues to move, the two discharge circuits tend to become balanced but remain slightly out of balance, so that there is a gradual follow-up by the lamp voltage of the voltage controlled by the fader arm 26 and the sender arms I0, I0, I9.

As previously stated herein, and as will be apparent, the control system of Fig. 2, aforedescribed, affords a character of illumination intensity control similanto that afforded by the control system of Fig. 1.

It will be obvious to those skilled in the art that the sender arm taps which are shown as being connected between the fader resistor sections may be rendered adjustable to vary the characteristics and rates of illumination intensity changes between the values preselected by the respective sender arms.

A convenient arrangement of the sender arms upon a control'panel I 21 is illustrated in Fig. 3. It should be noted that the sender arms are arranged in a manner whereby the sets of arms associated with the respective lamp groups serve to visually indicate by their relative positions the degree and character of changes of illumination intensity to be effected sequentially in respect of the several groups of lamps, and the relative rates at which suchchanges are to be effected, as shown in Fig. 3 by the dotted lines projected between the several sender arm handles.

A removable gag plate I28 is shown mounted on the control panel I2'I, said gag plate being provided with slots I29, which accommodate the projecting handles of the sender arms I0, I0, I9, II, 34, 35, I2, 54', 55. Slots I29 are arranged alternately with respect to the slots I30, within which the adjustable latch members I3I are adapted to slide.

After a desired illumination effect is obtained by movement of the respective sender arms to various trial positions, the gag plate I28 is set in place on the panel and the latch members I3I are moved into and clamped in positions corresponding to the instant positions of the sender arms. Latch members I3I may serve merely as markers, or may be provided with means engageable with the sender arms to definitely position the same. Thus by means of a multiplicity of gag plates any number of illumination effects may be registered and subsequently repeated without the necessity of again having to obtain the desired effects by trial manipulation of the sender arms.

The gag plate I28 and the latch members I3I may be and preferably are similar to the gag plate and latch members shown and described in my patent, No. 1,932,040, dated October 24, 1933.

While the system shown in Fig. 2 will operate satisfactorily with the sending rheostats and the fader resistor sections being of such ohmic values relative. to each other as are suitable to effect operation of the polarized relay of Fig. 1, it is to be understood that in practice fader resistor sections of relatively greater ohmic value are employed, since the grid control instrumentalities, consisting of the energy storage discharge network, are very much more sensitive than the polarized relay and therefore require a relatively smaller current to operate, as is well known. Moreover, it will be apparent to those skilled in theart that the actual voltage curve obtained with the system of Fig. 1 will depart slightly from an exact linear curve, but that the system of Fig. 2 will provide a voltage curve which followsyery closelyv the curve of illumination intensity which is shown in Fig. 4. Thus, if an extremely exact curve of illumination intensity is required, the system shown in Fig. 2 would be preferable. However, since the important consideration is the visual effect or effect upon the eye of an observer, slight departures of the voltage in the lamp circuit from an exact linear curve are of practically no consequence, since there is little or no observable effect of variation of illumination intensity of the lamps due to such departures in voltage.

What I claim as new and desire to secure by Letters Patent is:

1. In a control system, in combination, a load circuit having a connection with a source of constant potential, regulating means for said load circuit, means for operating said regulating means to vary the degree of energization of said load circuit, said operating means comprising sending means and receiving means connected with the latter in the form of a balancing control circuit, said sending means comprising a plurality of variable potentiometer resistors connected in parallel for preselecting a plurality of values of potential to be derived from said source, each of said values determining a point of balance of said control circuit, whereby given degrees of energization of said load circuit are selected, a fader resistor comprising a plurality of resistor sections connected in an electrically closed loop, the extremities of each of said resistor sections being subjected respectively to certain of said selected potential values, a fader contact arm cooperating with said fader resistor and movable with respect thereto to gradually vary the potential between the preselected values for each fader resistor section in increments or decrements substantially proportional to the difference in said values, whereby the point of balance of said control circuit is gradually changed with respect to said determined points, and associated means operable by unbalance of said circuit automatically to restore balance of said control circuit at the point determined by the position of. said fader contact arm, and simultaneously to operate said regulating means to subject said load circuit to a varying degree of energization having a direct relationship to said control potential.

2. In a control system, in combination, a load circuit having a connection with a source of constant potential, regulating means for said load circuit, means for operating said regulating means, said operating means comprising a plurality of resistors connected in parallel across a suitable source, each of said resistors having a cooperating contact arm presettable to select a control potential, a fader resistor connected in an electrically closed loop to which said contact arms are connected at spaced points, a cooperating fader arm movable with respect to said fader resistor to gradually vary the potential between the selected potentials in increments or decrements substantially proportional to the difference in the values of the selected potentials, means connected with the aforesaid resistors in the form of a balancing control circuit, the point of balance of said control circuit being gradually changed by variation of said control potential, and associated means responsive-automatically to unbalance of said control circuit to restore balance thereof, said last mentioned means being operable simultaneously to operate said regulating means to subject said load circuit to a varying degree of energization having a direct relationship to said varying control potential.

3. The combination with an illumination circuit to be supplied from a suitable source, of regulating means for varying the degree of energization of said illumination circuit, operating means for said regulating means, said operating means including sending means and receiving means connected with the latter in the form of a balancing control circuit, said sending means comprising a plurality of sending resistors the terminals of which are subjected to like degrees of potential, each of said resistors having a sender arm associated therewith and movable with respect thereto for preselecting values of control potential, whereby given points of balance of said control circuit are determined, means for gradually changing the point of balance of said control circuit with respect to said predetermined points, said last mentioned means comprising a fader resistor connected in an electrically closed loop to which said sender arms are connected at spaced points, a fader arm associated with said fader resistor and movable with respect thereto, whereby said control potential is adapted to be varied substantially rectilinearly between said preselected values, and associated means operable by unbalance of said control circuit automatically to restore balance thereof, and simultaneously to operate said regulating means to subject said illumination circuit to a varying degree of energization in accordance with variation of said control potential.

4. The combination with an illumination circuit to be supplied from a suitable source, of a fader resistor connected in an electrically closed loop, means comprising a plurality of sending rheostats connected in parallel across said source and each having an adjustable sender arm associated therewith, said sender arms being electrically connected with said fader resistor at spaced points on the latter whereby said fader resistor is connected with said source, said means being adapted to subject the fader resistor at said points of connection to selected values of potential, an adjustable contact arm associated with said fader resistor, and means associated with said contact arm for subjecting said illumination circuit to potential conditions which are the effect of the differential value of a plurality of said selected potential values as modified by a selected value of the resistance of one of said fader resistor sections.

5. The combination with an illumination circuit to be supplied from a source of constant potential, of. regulating means for said circuit, operating, means for said regulating means including sending means and receiving means connected with the latter in the form of a balancing control circuit and associated means operable by unbalance of said control circuit automatically to restore balance thereof, and simultaneously to operate said regulating means to subject said illumination circuit to a degree of energization determined by the point of balance of said control circuit, said sending means comprising a plurality of sending rheostats connected in parallel across said source and each having an adjustable sender arm associated therewith for determining a point of balance of said control circuit, a fader resistor having a plurality of resistor sections connected in the form of an electrically closed loop, said sender arms being connected to the extremities of said fader resistor sections, respectively, and a fader arm associated with said fader resistor and adapted to traverse said fader resistor sections in sequence to gradually change the point of balance of said control circuit with respect to said predetermined points of balance, whereby the degree of 'energization of said illumination circuit is varied substantially rectilinearly between values corresponding to said predetermined points of balance.

6. The combination with an illumination control circuit to be supplied from a source, of constant potential, of means for regulating the degree of energization of said illumination circuit, means for operating said regulating means, said operating means comprising sending means and receiving means connected with the latter in the form of a balancing control circuit, said sending means comprising a plurality of sending rheostats connected in parallel across said source, each of said sending rheostats having an associated sender arm movable with respect thereto to select a value of control potential,

whereby to determine a point of balance: of said control circuit, a. fader resistor having a number of resistor sections corresponding to the number of said sending rheostats, said resistor sections being connected in an electrically closed loop, the extremities of said resistor sections being connected to the respective sender arms, said fader resistor having an,associated fader arm adapted to traverse said resistor sections in sequence to vary said control potential substantially rectilinearly with respect to said selected values, whereby to provide for gradually changing the point of balance of said control circuit within the ranges defined by said predetermined points of balance, and associated means responsive to unbalance of said control circuit automatically to restore or to tend to restore balance thereof and simultaneously to operate said regulating means, whereby the degree of 'energization of said illumination circuit is sustained or varied as the point of balance of said control circuit is sustained or varied.

7. In an illumination control system, in combination, a group of electric lamps to be supplied from a source of constant potential, illumination intensity regulating means for said lamps, means for (operating said regulating means, said operating means comprising sending means and receiving means connected with the latter in the form of a balancing control circuit, said sending means comprising a plurality of sending rheostats connected in parallel across said source, each of said sending rheostats hav ing an associated sender arm movable with respect thereto to select a value of control potential, whereby to predetermine a point of balance of said control circuit which determines a given intensity of illumination of said lamps, a fader resistor having a number of resistor sections corresponding to the number of said sending rheostats, said fader resistor sections being connected in an electrically closed loop, the extremities of said resistor sections being connected respectively to said sender arms, said fader resistor having an associated fader arm adapted to be moved continuously over said resistor sections in sequence to vary said control potential substantially rectilinearly with respect to said selected values, whereby to provide for continuousiy changing the point of balance of said control circuit within the ranges defined by said predetermined points of balance, and associated means responsive to unbalance of said control circuit automatically to tend to restore balance thereof and simultaneously to operate said regulating means, whereby the intensity of illumination or said lamps is continuously varied substantially rectilinearly with respect to the intensity values deflned by said predetermined points of balance of said control circuit.

8. In an illumination control system, in combination, a plurality of groups of electric lamps to be supplied from a source of constant potential, illumination intensity regulating nieans for each of said groups of lamps, operating means for each of said regulating means, said operating means comprising sending means and receiving means connected with the latter in the form of a balancing control circuit, each of said sending means comprising a plurality of sending rheostats connected in parallel across a suitable source, each of said sending rheostats having an associated sender arm movable with respect thereto to select a value of control potential, whereby to predetermine a point of balance of said control circuit which determines a given intensity of illumination of its associated group of lamps, a fader resistor having a number of resistor sections corresponding to the number of 7 said sending rheostats, said fader resistor sections being connected in an electrically closed loop to which said sender arms are respectively connected at the points of connection of said sections, said fader resistor having an associated fader arm movable with respect thereto, means for moving said fader arms jointly with respect to said fader resistors, whereby to provide for joint and substantially rectilinear variation of the control potential for each of said control circuits betweensaid selected values, whereby the points of balance of the respective control circuits are adapted to be changed within the ranges defined by said predetermined points of balance, and means associated with each of said control circuits and responsive to unbalance thereof automatically to restore or to tend to restore said balance, said last mentioned means being operable simultaneously to operate said regulating means, .whereby the intensity or illumination ,of each of said groups of lamps is varied independently of the variations in illumination intensity being effected in each of the other of said groups, said intensity of illumination being varied substantially rectilinearly between the intensity values defined by said predetermined polnts of balance of the respective control circuits.

9. In an illumination control system,'in combination, a group of electric lamps to be supplied from a source of constantpotential, illumination intensity regulating means for said lamps, meam for operating said regulating means, 'said operating means comprising a plurality of sending impedances connected in parallel across said source, each of said sending impedances having an adjustable sender arm associated therewith,

a receiving impedance connected in parallel with said sending impedances and having an adjustable receiver arm associated therewith, a fader resistor having a number of sections corresponding to the number of said sending impedances, said fader resistor sections being connected in an electrically closed loop to which said sender arms are respectively connected at the points of connection of said sections, said fader resistor hav ing an adjustable fader arm associated therewith, a polarized relay coil connected between said fader arm and said receiver arm, said sending impedance, receiving impedance, fader resistor and polarized relay coil forming a Wheatstone bridge, said sender arms being each effective to determine a point of balance of said bridge whereby to select given intensities of illumination, respectively, for said lamps, said fader arm being effective to gradually change the point of balance of said bridge within the ranges defined by said predetermined'points of balance, whereby to vary the intensity of illumination of said lamps with respect to the values of intensity defined by said predetermined points of balance of said bridge, and means associated with said polarized relay coil and said receiver arm and operable by unbalance of said bridge automatically to efiect adjustment of said receiver arm to restore or to tend to restore balance of said bridge, and simultaneously to operate said regulating means to provide for said variation in the illumination intensity of said lamps.

10. In illumination intensity control apparatus, the combination with a group of electric lamps to be supplied from a suitable source, illumination intensity regulating means for said lamps, means for operating said regulating means, said last mentioned means comprising sending means and receiving means connected with the latter in the form of a balancing control circuit, said sending means comrising a plurality of sending irnpedances connected in parallel across said source, each of said sending impedances having an associated sender arm' movable with respect thereto to determine a point of balance of said control circuit, whereby to select given intensities of illumination, respectively, for said lamps, a fader resistor having a number of resistor sections corresponding to the number of said sending impedances, said resistor sections being connected in an electrically closed loop. to which, said sender arms are connected at v the points of connection of said resistor sections,

said fader resistor having an associated fader arm adapted to be moved continuously over said resistor sections in sequence to gradually change the point of balance ofsaid control circuit within the ranges defined by said predetermined points of balance, and associated means operable by unbalance of said control circuit automatically to tend to restore balance thereof and simultaneously to operate said regulating means to provide for variation of the intensity of illumination 01' said lamps between the values defined by said predetermined points of balance of said control circuit, said sender arms being so arranged, in side by side relationship, as to indicate the respective intensities of illumination preselected for said lamps by their positions in their respective paths of movement and to indicate the sequence in which said intensities are enacted by said lamps, the arrangement and relative positions of said arms being also such as to indicate the relative rates at which the intensity of illumination of said lamps is varied between the preselected values, the arrangement of said arms being such as to visually indicate in a graphic manner, by their positions relatively to each other, the cycle of illumination intensity variation which said group of lamps is to afford.

11. In an illumination control system, in combination, a group of electric lamps, a variable reactor for regulating the intensity. of illumination of said lamps, means comprising an electric valve having a control grid and adapted to vary the impedance of said reactor in accordance with the voltage impressed on said grid, means comprising an energy storage element for impressing a variable voltage on said grid, means for charging and discharging said element, a plurality of sending potentiometer rheostats connected in parallel and each having an associated sender arm movable with respect thereto to preselect a value of voltage to be impressed on said element, whereby to determine a given intensity of illumination of said lamps, a fader resistor having a number of resistance sections corresponding to the number of said sending rheostats, said resistance sections being connected in an electrically closed loop to which said sender arms are respectively connected at the points of connection of said resistance sections, said fader resistor having an associated fader arm adapted to be moved continuously and unidirectionally with respect thereto to gradually vary the voltage impressed on said energy storage element sequentially throughout the voltage ranges preselected by said sender arms, whereby to effect gradual variation of the intensity of illumination of said lamps between and inclusive of said predetermined intensities.

12. In an illumination control system, in combination, a group of electric lamps to be supplied from a source of constant potential, illumination intensity regulating means for said lamps, operating means for said regulating means including sending means and receiving means connected with the latter in the form of a balancing control circuit and associated means operable by unbalance of said control circuit automatically to restore balance thereof, and simultaneously to operate said regulating means to subject said lamps to a degree of energization determined by the point of balance of said control circuit, said sending means comprising a plurality of potentiometer resistors each having an adjustable sender arm associated therewith for determining a point of balance of said control circuit, a fader resistor having a plurality of resistor sections connected in an electrically closed loop, said sender arms being connected to the extremities of said fader resistor sections, respectively, and a fader arm associated with said fader resistor and adapted to traverse the sections thereof in sequence to gradually change the point of balance of said control circuit with respect to said predetermined points of balance, the resistance values of the control elements comprising said operating means being definitely proportioned with respect to each other, whereby upon movement of said fader arm the degree of energization of said lamps is varied substantially rectilinearly between the values corresponding to said predetermined points of balance.

RICHARDB.HUN'1'ER.

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