High intensity discharge lamp color

Claim 1

Apparatus for controlling the operation of one or more high intensity discharge lamps, each of said lamps having a photosensor associated therewith, said apparatus comprising: (a) an electronic high intensity discharge lamp power supply electrically connected to a power source and to said one or more high intensity discharge lamps; (b) each of said photosensors for producing an output signal representative of colour temperature in light output by said respective lamps, each of said photosensors further comprising first and second photodiodes, and a colour filter mountable between said second photodiode and said lamp associated with said photosensor; (c) a controller electrically connected between each of said photosensors and said power supply, said controller for receiving said output signals representative of colour temperature and for outputting power supply control signals for controlling operation of said one or more lamps to maintain a desired uniformity of colour temperature variation in light output by said one or more lamps; (d) for each lamp, colour signal feedback means electrically coupled between said first and second photodiodes and said controller, said colour signal feedback means for producing a signal representative of colour temperature variation, said colour signal feedback means further comprising: (i) a first variable gain amplifier electrically connected to said first photodiode for input to said first amplifier of a first signal output by said first photodiode in response to light intensity output by said lamp; (ii) a second variable gain amplifier electrically connected to said second photodiode for input to said second amplifier of a second signal output by said second photodiode in response to colour temperature of light output by said lamp; and, (iii) comparator means electrically connected to receive signals output by one of said amplifiers, to compare said amplifier output signals with a voltage reference signal and to output to each of said amplifiers a feedback signal for gain control of each of said amplifiers.