US2848654A - Brightiness controls for electric lamps - Google Patents

Description

J. w. STRANGE ETAL 2,4,54

BRIGHTNESS CONTROLS FOR ELECTRIC LAMPS Filed NOV. 14, 1950 '7 Sheets-Sheet 1 20/4 208 20: 30p 20E- 20F 20's 20] 20H 20M 20w OWN WILLIAM STRANGE) JOHN SHAPLAND LOCKYER} raj ll'lve htor s.

Af'kory g 1958 J. w. STRANGE ET AL 9 9 BRIGHTNESS CONTROLS FOR ELECTRIC LAMPS '7 Sheets-Sheet 2 Filed Nov. 14, 1950 JOHN WILLIAM 'STRANaE,

J'OHN SHAPLAND L OQK E A' to vnew i9, 195$ J. w, STRANGE ETAL 2,4$,54

BRIGHTNESS CONTROLS FOR ELECTRIC LAMPS Filed Nov. 14, 1950 7 Sheets-Sheet 3 JOHN \A ILUA STRANGE,

A'iforncg g- 19$ J. w. STRANGE ETAL' BRIGHTNESS CONTROLS FOR ELECTRIC LAMPS '7 Sheets-Sheet 4 Filed Nov. 14, 1-950 \](-)HN WILLIAM TRANQE,

Jo SHAPLAND YER,

In vewors v Aug. 19, 1958 .pw. STRANGE ETAL BRIGHTNESS CONTROLS FOR ELECTRIC LAMPS I 7 Sheets-Sheet 5 Filed Nov. 14,- 1950 JOHN HAPLAIVD LOCI/(YER,

I n ven vrr'. mm

Aug. 19, 1958 J. w. STRANGE ETAL BRIGHTNESS CONTROLS FOR ELECTRIC LAMPS Filed Nov. 14, 1950 'T Sheets-Sheet 6 l/l/ lll/l/fil/ K! J)! Joe-m WILLIAM 'rfiAlvea mmmwm a 55 H K] In vewa r4. W Af'foi' h e Jaw SHAPLAWD LGCKYE Aug. 19, 1% J. w. STRANGE ETAL 2,848,654

BRIGHTNESS CONTROLS FOR ELECTRIC LAMPS 7 Sheets-Sheet '7 Filed Nov. 14, 1950 HA WILLIAM STRANGE, H SHAPLAND O KYER;

2,4,fii Patented Aug. 19, 1958 BRIGHTNESS CONTROLS FUR ELECTRIC LAMPS John William Strange and John Shapland Loclryer, London, England, assignors to Thorn Electrical industries Limited, London, England, a company of (Great Britain Application November 14, 1950, Serial No. 195,508

2 Qlaims. (Cl. 315317) This invention relates to brightness controls for electric lamps which may be low pressure discharge lamps-or incandescent filament lamps.

A brightness control for low-pressure discharge lamps has been proposed wherein a hot-cathode, low-pressure electric discharge lamp, a ballast choke and a variable impedance element are connected in series between the terminals of a power source. A filament transformer has a primary winding connected between the power source terminals and separate secondary windings connected to supply heating current continuously to the lamp electrodes whilst the lamp is in operation. The brightness of the lamp may be adjusted by varying the value of the variable impedance element.

Brightness controls for incandescent filament lamps are well known and usually consist of variable resistors connected in series with the lamp or group of lamps to be controlled.

Such brightness controls can be used, for example, when the lamps are used for stage lighting. It is desirable to be able to adjust at will the colour and the intensity of the light illuminating the stage. In one arrangement for obtaining colour variation a first series of lamps are coloured red and connected to one brightness control, another series are coloured blue and connected to a second brightness control, and the remaining lamps are coloured green and connected to a third brightness control, red, blue and green being primary colours. In a typical lighting plot the red control may be set to give full intensity, the blue to give half intensity and the green to give quarter intensity. If it is desired to alter the intensity of the lighting without any substantial change of colour the three controls must be operated simultaneously at rates such that the apparent brightness of the red, blue and green lamps is maintained approximately constant in the ratio 1 1 /2 1% respectively.

In one arrangement which has been proposed for use with incandescent filament lamps, the three separate brightness controls are connected in series with a master brightness control, and the master control alone is operated when it is desired to alter the intensity of the lighting. This method is not satisfactory and colour change cannot be avoided by its use since lamps of difli'erent colours do not change their apparent brightness by the same amount for the same change in their operating current. Also the arrangement is not applicable to lowpressure discharge lamps.

An object of this invention is to provide-brightness control means which enable the brightness of two or more lamps or series of lamps to be altered substantially simultaneously and in some predetermined ratio to each other.

According to this invention, a master brightness control for lamps includes means adapted to displace the control members of secondary brightness controls, each of which is adapted to be associated with a lamp or series of lamps of a particular colour, substantially simultaneously from a position corresponding to zero brightness towards predetermined positions at rates which are such functions of the required distances of displacement of the control members of the secondary brightness controls that the last-mentioned control members all reach the said predetermined positions at substantially the same instant, and means enabling said predetermined positions to be altered at will.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings wherein:

Fig. 1 is an elevational view of a first embodiment,

Fig. 1A is a schematic diagram of a variably tapped resistor for use with the embodiment in Fig. 1,

Fig. 2 is an end elevation of the embodiment in Fig. 1,

Fig. 3 is a section taken along the line 3-3 in Fig. 1,

Fig. 4 is an elevational view of a second embodiment,-

Fig. 5 is a plan view of a part of the embodiment in Fig. 4,

Fig. 6 is an elevational view of a third embodiment,

Figs. 7 and 8 are sections taken along the lines 7-7 and 8-i respectively in Fig. 6,

Figs. 9, 10, 11 and 12 are sections taken along the lines 9-9, ltll.0, 1ll-lll and l2-12 respectively in Fig. 7, and

Fig. 13 is a section taken along the line l3-l3 in Fig. 8.

In the first embodiment shown in Figs. 1 to 3 of the drawings, each secondary brightness control is a variablytapped resistor consisting of a series of separate resistor elements 20A, 28B, 20C etc. connected to a series of tapping contacts 21A, 21B, 210 etc. over which a control contact 22 slides. A master brightness control includes three parallel panels 23 spaced from each other and fixed to a baseboard 24. The panels are held rigidly apart by three screw bolts 25 fitted with six tubular spacing pieces 25A. The tapping contacts 21 consist of metal L-shaped pieces (see Fig. 3) inset into a rectangular bar 26 of insulating material, each bar 26 being held between two brackets 27 fixed to the adjacent panel 23 and each tapping contact 21 being provided with a terminal screw 28. Two pairs of brackets 29 are fixed to each panel 23 and support two longitudinal parallel guides 30. A carriage 31 rides on each guide 30, the two adjacent carriages being rigidly connected by a transverse yoke 32.

A control member in the form of a control contact 22 is formed by five resilient fingers fixed to their adjacent carriage 31 and insulated therefrom, the fingers being bent to engage the tapping contacts 21. The control contact is electrically connected to a terminal 22A by a flexible lead 22B. Each secondary brightness control includes an arm 34 pivoted about a pin 35 which is fixed to its respective panel 23. The three arms of the master control are rigidly connected together at their outer ends by a cr0ss-piece 36. The cross piece also serves as a support for the outer ends of three threaded rods 37, which are disposed parallel with and respectively close to the three arms 34. The rods are rotatably mounted in the inner ends of the arms 34 and in the cross-piece 36 and can each be rotated by means of an hand-wheel 33. A nut 39 is mounted on each rod 34 and is provided with a stud 40 engaging a longitudinal slot 41 in its respective transverse yoke 32. The nut 39 is also provided with a pin 42 engaging a slot 43 in the arm 34 to prevent ro tation of the nut about the rod, thus rotation of the rod 37 by means of its handwheel 38 causes movement of the nut 39 along the rod to any required position. It will be apparent that such movement of the nut 39 causes movement of the transverse yoke 32 longitudinally on its guides 30. Also the arrangement is such that movement of each arm 34 moves its associated transverse yoke 32 longitudinally on its guides and thus moves the control contact 22. The dimensions of the apparatus are made such that, when the stud 40 is furthest from the pin 35, displacement of the arm 44 through approximately 60 moves the control contact 22 from an extreme position corresponding to zero brightness to another extreme position corresponding to full brightness. The distance through which the control contact is displaced upon displacement of the arm 44 through approximately 60 can be adjusted by moving the nut 39, and thus the stud 46, along the arm.

Any number of secondary brightness controls can have their arms connected to a common cross piece or to a suitable equivalent operatcrs control and thus be operated simultaneously. it will be understood that each brightness control can be present e. g. while at the zero brightness position, by rotating the respective handwheel 38 so as to move its associated nut 39 to the required position on the rod 27. The secondary control members are moved simultaneously by movement of the operators control (i. e. the cross-piece 26) and at rates which are such a function of the respective distances of the nuts 29 from the pins 25 that the control contacts 12 will all reach their intended operative positions at the same instant, upon completion of the movement of the arm through approximately 60. The values of the separate resistor elements 10 are preferably made such that the ratio of the angular movement of each arm 24 to the apparent brightness of the associated lamp or lamps has a constant value. It is comparatively easy to design a single continuously variable resistor element for use with incandescent filament lamps and having the characteristic required to obtain the said constant ratio but it is more difiicult to design such a resistor element for use with low-pressure discharge lamps owing to the much wider range of resistance required and it is therefore preferable to use separate resistor elements connected between tapping studs.

In the second embodiment shown in Figs. 4 and an arm 44 is mounted on a horizontal shaft 45 carried by a bearing fixed to one corner of one of two end pieces 46 of a flat vertical contact assembly, which is in turn fixed to a baseboard 47. The two end pieces 46 are of insulating material and the arm 44 is fixed to the shaft 45 by a grub screw 44A. The contact assembly consists of alternate strips of metal 48A, 48B etc. and insulating material 49A, 493 etc. placed face to face and clamped together by two insulated bolts 5%. The edges of the metal strips are exposed on a vertical face and constitute the fixed contacts of a variably-tapped resistor, and separate resistor elements are connected between each adjacent pair of strips by means of terminal screws 51. A stud 52 provided with a handle 53 of insulating material is slidable in a longitudinal slot 54 in the arm 434 and can be moved to any point along the arm. The stud acts as a tapping contact for the secondary brightness control and is held in contact with one face of the con tact assembly by means of a spring washer 55 on the rod 45. The contact assembly is made sutficiently large to ensure that the stud remains in contact with the vertical face during movement of the arm. It is arranged that with the stud at its farthest position along the arm a rotation of the shaft through approximately 60 will move the stud from the zero brightness position to the full brightness position. Any number of arms, each associated with a separate contact assembly, may be fixed on the shaft 45 and operated simultaneously by a single operators master control, e. g. a handle 56 of insulating material which is fitted to one of the arms As in the first embodiment the values of the separate resistor elements are preferably such that the ratio of movement of the arm/ apparent brightness of the associated lamp or lamps is approximately constant. In use, the brightness controls are preset for the desired value, in a similar manner to the first-mentioned embodiment, by moving the stud 52 by hand along the arm 44.

In the third embodiment shown in Figs. 6 to 13, as in the previous two embodiments, each secondary brightness control is a variably tapped resistor. A master brightness control includes a casing 57 divided into three compartments by two partitions 58, each compartment containing an arcuate rectangular section bar 59 which supports tapping contacts 60. Each tapping contact is provided with a terminal screw 61. The control membet for a secondary brightness control consists of a metal arm 62, mounted on a shaft 63 and capable of free rotation about the shaft. The control contact 64 consists of a carbon brush 65 mounted in the arm 61 and springbiased into engagement with the tapping contacts 60, the arm being provided at a point near to the shaft 63 with a terminal screw 66 to which a flexible lead can be connected. The arm 62 terminates at its free end in a spigot 67 over which an operators handle 63 of insulat ing material is fitted.

A collar 69 of insulating material is pinned to the arm and serves as an anchorage for a helical spring 70 which has its other end fastened to a bracket 71 fixed to the casing 57. The helical spring biases a cam-follower 72 on the arm into contact with one of a nest 73 of six edge cams 74A, 748 etc. The nest 73 is mounted on a shaft 75, relative rotation of the shaft and the nest being prevented by a key 76, and is movable axially along the shaft. The nest is moved by means of an operators handle 77 rigidly connected to a yoke 78 which is pivoted on the shaft and embraces the nest. A plate 79 connecting the yoke and the handle 77 can be fitted into any one of six slots 80A, 80B, etc. in a block 81, each slot corresponding to one of the six edge cams, which are set at different depths in the nest. The cam follower 72 is mounted in an insulating bush 32 (Fig. 12) which is in turn fitted in the arm 62, the cam follower "being thus insulated from the arm. The end of the cam follower which engages the edge cams is fitted with a roller 83.

The three nests 73 of the master control can be rotated simultaneously through a maximum of about by an operators control handle 84 (Fig. 6) fixed to one end of the shaft 75. Each secondary brightness control member can be preset while at the Zero position by moving the nest 73 until the plate 79 can be lowered into the slot 80 corresponding to the cam desired track 74. The control member can be preset while at a position other than the zero position by moving the nest to the extreme left, as seen in Fig. 6, to disengage the cam follower from the nest. Thereafter, the arm 62 is moved to the required position (e. g. that of the middle arm 62 in Fig. 6 which corresponds to half maximum brightness) and the plate 79 is moved to the right until it can be engaged in the requisite slot 80, whereupon the cam follower is in engagement with the required cam track 74. In this embodiment the angle through which each arm 62 is rotated upon rotation of its associated nest through about 90 can be varied in five discrete steps between 0 and about 60, rotation of the arm 62 through about 60 causing displacement of the control contact 64 from one extreme position corresponding to zero brightness to another corresponding to full brightness.

Any number of arms 62 and cam nests 73, etc. can be provided and thus be operated simultaneously by a single operators master control e. g. the handle 84.

As in the two previous embodiments the values of the separate resistor elements are preferably such that the ratio of displacement of the arm 62/apparent brightness of the associated lamp or lamps is approximately constant.

We claim:

1. A master brightness control for lamps including means adapted to displace the control members of secondary brightness controls. each of which is adapted to be associated with a lamp or series of lamps of a particular colour substantially simultaneously from a position corresponding to zero brightness towards predetermined positions at rates which are such functions of the required distances of displacement of the control members of the secondary brightness controls that the last-mentioned control members all reach the said predetermined positions at substantially the same instant, and means enabling said predetermined positions to be altered at will, wherein each control member includes a contact movable along a contact assembly upon displacement of an arm, and means for displacing the arm constituted by a movably mounted nest of cams each of which cams is engageable with a cam follower operatively connected to the arm simultaneously, and wherein the means enabling the said predetermined positions to be altered at will are constituted by means for engaging the cam follower with any selected cam of the nest.

2. A master brightness control for a group of lamps of different colors, including impedance means for fixing the current through each lamp independently to permit selection of a particular color mixture from the group of lamps of different colors; and means for varying all of said impedance means simultaneously and proportionately to reduce the brightness of the light from the group while keeping the color mixture constant.

References Cited in the file of this patent UNITED STATES PATENTS 1,194,451 Wiegand Aug. 15, 1916 1,759,903 Hunter May 27, 1930 1,955,906 Crouse Apr. 24, 1934 2,192,673 Cooper Mar. 5, 1940 2,220,951 Borden Nov. 12, 1940 FOREIGN PATENTS 389,889 Germany Feb. 15, 1924 679,393 Germany Aug. 4, 1939

Images