Lamp brightness control circuit with ambient light compensation

• US 5,404,080 A
• Filed: 07/05/1994
• Issued: 04/04/1995
• Est. Priority Date: 09/21/1989
• Status: Expired due to Fees

• Current Assignee: Emergent Business Capital, Inc., The Tell Ertl Family Trust
• Original Assignee: Etta Industries, Inc.
• Inventors: Quazi, Fazle
• Primary Examiner(s): Pascal, Robert J.
• Assistant Examiner(s): DINH, TAN X
• Application Number:
  US08/270,312
• Time in Patent Office: 273 Days
• Field of Search: 315/151, 315/158, 315/156, 315/150, 315/152, 315/154, 315/155, 315/157, 315/159
• US Class Current: 315/151
• CPC Class Codes: F21V 23/0464 the sensor sensing the level of ambient illumination, e.g. dawn or dusk sensors
• CPC Class Codes: H05B 41/2925 against abnormal lamp operating conditions
• CPC Class Codes: H05B 41/3922 and measurement of the incident light
• CPC Class Codes: H05B 41/3927 by pulse width modulation H05B41/3922 takes precedence
• CPC Class Codes: Y10S 315/04 Dimming circuit for fluorescent lamps

Abstract

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

Claims

1. A lighting control device for use with an area lighting fixture including a lamp and a, dimming circuit for reducing brightness of the lamp depending on the amount of sunlight present to maintain a desired amount of light in an area lit by the area lighting fixture, comprising:

collecting means for collecting ambient light representing a lighting level in said area including sunlight;

flexible cable means having first and second ends, the first end connected to the collecting means in light transmission relationship for receiving and carrying the sunlight collected by the collecting means;

photocell circuit means connected to the second end of the flexible cable means and adapted to be connected to the dimming circuit, for receiving said sunlight from the flexible cable, generating a variable dimming control signal varying with the amount of sunlight available to the area, and transmitting said dimming control signal to said lighting fixture dimming circuit to effect reduction of said lamp brightness in response to an increase in available sunlight.

2. The device of claim 1, wherein said collecting means is adapted for installation in a ceiling proximate to the lighting fixture.

3. The device of claim 2 wherein said collecting means includes locking means for fixing the collecting means in an installation hole formed in a grid-type ceiling panel.

4. The device of claim 3, wherein said collecting means is adapted to collect light primarily from one direction.

5. The device of claim 4 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.

6. The device of claim 5 wherein the prismatic lens has at least two reflective surfaces, one at about a 30 degree angle with respect to the receiving surface and the other at about a 60 degree angle with respect to the receiving surface.

7. The device of claim 3, wherein the collecting means comprises a threaded tube with two ends which receives 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.

8. The device of claim 7 wherein said locking means include nuts threaded onto the outside of said tube to hold the tube in a hole provided therefor.

9. The device of claim 7 wherein the ambient light-collecting lens is threaded for installation into the one end of the tube.

10. The device of claim 7 further including cable locking means for holding the flexible cable means in a fixed position relative to the tube.

11. The device of claim 10 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.

12. The device of claim 2 wherein said photocell circuit means is contained in a housing adapted for connection to the lighting fixture through a standard knockout plug.

13. The device of claim 12 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.

14. The device of claim 13 further including cable locking means for holding the flexible cable means in a fixed position relative to the housing tube.

15. The device of claim 14 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.

16. The device of claim 12 wherein said photocell circuit means includes a sensitivity adjustment adjustable from the housing exterior.

17. The device of claim 1 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.

18. The lighting control device of claim 1, further comprising a control circuit connected to said lighting fixture dimming circuit for generating a low-power, variable DC control input voltage which is applied to a control input of a power circuit to control the brightness of the lamp, said control circuit comprising control pulse generating means for generating control pulses of variable duty cycle;

brightness control means connected to the control pulse generating means for setting the desired brightness of the lamp; and

integrating means, connected between the power circuit control input and the control pulse generating means, for integrating the variable-width control pulses of the control pulse generating means to produce said variable DC control input voltage to the control input of the power circuit.

19. The lighting control device of claim 18 wherein said photocell circuit means is connected to said control circuit so that said variable dimming control signal produced by said photocell circuit means is integrated along with said variable duty cycle control pulses to generate said variable DC control input voltage.

20. The lighting control device of claim 19 wherein the control output of a single said photocell circuit means is connected to a plurality of said control circuits.

21. The lighting control device of claim 18 wherein the brightness control means and the photocell circuit means are both connected to a common input terminal of the control pulse generating means such that the brightness control means and the photocell circuit means simultaneously affect the brightness of the lamp load.

22. The lighting control device of claim 18 wherein said control pulse generating means comprises a single integrated circuit pulse width modulator.

23. The lighting control device of claim 22 wherein said photocell circuit means is connected to said control circuit so that said variable dimming control signal produced by said photocell circuit means is integrated along with said variable duty cycle control pulses to generate said variable DC control input voltage.

24. The device of claim 1 wherein said photocell circuit means further comprises light equalizing means for reducing the brightness of the lighting fixture as ambient light from said other source increases and for increasing the brightness of the lighting fixture as ambient light from said other source decreases, to compensate for variations in light available from said other source and maintain a perceptively constant total light level in the area.

25. A method of saving energy used by a lighting fixture including a lamp and an associated dimming circuit for variably controlling brightness of the lamp to provide a desired amount of light to an area, comprising the steps of:

providing an apparatus comprising collecting means for collecting ambient light representing a lighting level in the area including sunlight flexible cable means having first and second ends, the first end connected to the collecting means in light transmission relationship for receiving and carrying sunlight collected by the collecting means; and

photocell circuit means connected to the second end of the flexible cable means and adapted to be connected to the dimming circuit, for receiving said ambient light from the flexible cable, generating a variable dimming control signal varying with the amount of sunlight, and transmitting said dimming control signal to said lighting fixture dimming circuit to effect reduction of said lamp brightness in response to an increase in available ambient light from the source other than the lighting fixture;

positioning the collecting means to collect at least sunlight;

operating the apparatus to reduce the brightness of the lighting fixture as available sunlight increases and to increase the brightness of the lighting fixture as available sunlight decreases, to compensate for variations in available sunlight and maintain a perceptively constant total light level in the area, whereby total energy consumption of the lighting fixture is reduced.