Lamp brightness control circuit with ambient light compensation

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.

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.

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.