Lamp brightness control circuit with ambient light compensation

• US 5,581,158 A
• Filed: 04/03/1995
• Issued: 12/03/1996
• Est. Priority Date: 09/21/1989
• Status: Expired due to Fees

• Current Assignee: Etta Industries, Inc.
• Original Assignee: Etta Industries, Inc.
• Inventors: Quazi, Fazle
• Primary Examiner(s): Gonzalez, Frank
• Assistant Examiner(s): Ratliff, Reginald A.
• Application Number:
  US08/415,212
• Time in Patent Office: 610 Days
• Field of Search: 315/307, 315/308, 315/224, 315/DIG. 4, 315/291, 315/149
• US Class Current: 315/149
• 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 system for gas discharge lamps, comprising:

an inverter circuit having a control input, a power input, and a plurality of switching mechanisms connected to alternately provide positive and negative voltage to a gas discharge lamp load, with the switching mechanisms controlled to vary a duty cycle of power supplied from said power input to the lamp load in response to the level of a low-power, variable DC control input voltage applied to the control input;

a 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 load; and

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

an ambient light sensing circuit connected to the control pulse generating means for sensing the ambient light level and producing a variable control output depending on the ambient light level;

wherein the control pulse generating means varies the duty cycle of the control pulses with the control output of the ambient light sensing circuit such that the brightness of the gas discharge lamp load is decreased when the amount of available ambient light increases.

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

6. The system of claim 1 wherein the control pulse generating means comprises a single integrated circuit pulse width modulator which varies the duty cycle of the control pulses according to the control output of the ambient light sensing circuit.

2. A lighting control system for gas discharge lamps, comprising:

a plurality of control circuits each for controlling a power circuit wherein the power circuit supplies power variably to a gas discharge lamp load in response to the level of a low-power, variable DC control input voltage applied to a control input of the power circuit, said control circuits 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 load; 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 the variable DC control input voltage to the control input of the power circuit;

an ambient light sensing circuit connected to a plurality of said control pulse generating means for sensing the ambient light level, producing a variable control output, and transmitting said variable control output to said plurality of control pulse generating means depending on the ambient light level;

wherein each control pulse generating means varies the duty cycle of the control pulses with the control output of the ambient light sensing circuit such that the brightness of the gas discharge lamp load is decreased when the amount of available ambient light increases.

3. A lighting control system for gas discharge lamps, comprising:

a control circuit for controlling a power circuit wherein the power circuit supplies power variably to a gas discharge lamp load in response to the level of a low-power, variable DC control input voltage applied to a control input of the power circuit, said control circuit comprising control pulse generating means for generating control pulses of variable duty cycle;

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

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

an ambient light sensing circuit connected to the control pulse generating means for sensing the ambient light level and producing a variable control output depending on the ambient light level;

wherein the control pulse generating means varies the duty cycle of the control pulses with the control output of the ambient light sensing circuit such that the brightness of the gas discharge lamp load is decreased when the amount of available ambient light increases, and

wherein the ambient light sensing circuit comprises;

a lens adapted to collect light primarily from an ambient source other than said gas discharge lamps;

a fiber optic cable connected to said lens and to a circuit housing for transmitting light from the lens to the housing;

wherein the housing contains a photocell circuit comprising a photocell and a sensitivity adjustment potentiometer, with the photocell circuit producing the control output of the ambient light sensing circuit in response to light received by said lens.

5. A lighting control system for gas discharge lamps, comprising:

a control circuit for controlling a power circuit wherein the power circuit supplies power variably to a gas discharge lamp load in response to the level of a low-power, variable DC control input voltage applied to a control input of the power circuit, said control circuit comprising control pulse generating means for generating control pulses of variable duty cycle;

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

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

an ambient light sensing circuit connected to the control pulse generating means for sensing the ambient light level and producing a variable control output depending on the ambient light level;

wherein the control pulse generating means varies the duty cycle of the control pulses with the control output of the ambient light sensing circuit such that the brightness of the gas discharge lamp load is decreased when the amount of available ambient light increases, and

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