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Uniform Illumination Control for Fluorescent Lamps

IP.com Disclosure Number: IPCOM000053058D
Original Publication Date: 1981-Aug-01
Included in the Prior Art Database: 2005-Feb-12
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Van Hook, DA: AUTHOR

Abstract

Fluorescent lamps tend to have a nonuniform illumination pattern along their length. This nonuniform illumination can be corrected by changing the duty cycle of the AC signal driving the lamp so that there is an inequality during each cycle of the AC current flow in each direction in the lamp. The illumination uniformity may be sensed by a CCD (charge-coupled device) array and processed by a microprocessor to control the duty cycle of the AC signal driving the lamp.

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Uniform Illumination Control for Fluorescent Lamps

Fluorescent lamps tend to have a nonuniform illumination pattern along their length. This nonuniform illumination can be corrected by changing the duty cycle of the AC signal driving the lamp so that there is an inequality during each cycle of the AC current flow in each direction in the lamp. The illumination uniformity may be sensed by a CCD (charge-coupled device) array and processed by a microprocessor to control the duty cycle of the AC signal driving the lamp.

Shown above is a fluorescent lamp 10 driven by an AC lamp regulator 12. Light from the lamp is collected by lens 14 and focused as a line of light on a C:CD array 16. The illumination signal for each cell in the array 16 is passed to an analog-to-digital converter 18. Converter 18 digitizes the analog signal from each cell. Microprocessor 20 monitors the illumination level from each cell.

Microprocessor 20 can detect the variation in uniformity along the length of lamp 10, and generate a digital signal to control the duty cycle of the AC signal driving the lamp 10. The digital control signal from microprocessor 20 is converted to an analog voltage level by the digital-to-analog converter 22. This voltage level is compared against a sawtooth waveform by comparator 24. The output of comparator 24 will be a cyclic waveform of variable duty cycle depending upon the level of the analog signal from the digital-to-analog converter
22. This variable duty cycl...