Optics: measuring and testing – Photometers – Photoelectric
Patent
1994-11-22
1996-08-20
Gonzalez, Frank
Optics: measuring and testing
Photometers
Photoelectric
356221, 356223, 356224, 250214P, 354425, G01J 142
Patent
active
055483984
ABSTRACT:
An illuminant discriminator distinguishes a range of separate illuminants, including high efficiency fluorescent lighting, by modifying the frequency response of a signal output from a photodetector. A switchable high pass filter coupled to the photodetector has a first filter section with a first cutoff characteristic selected to pass signal components due to various types of lighting including high efficiency lighting, and a second section with second cutoff characteristic that separates out the high efficiency components. The high pass output is processed by a log amplifier to develop flicker frequency harmonics that are distinguished as to source illuminant by comparator stages. Undersampling artifacts due to high efficiency lighting are present in the mixed illuminant spectrum when the first filter section is operative, and positively identified as high efficiency lighting when the second section is operative. Consequently, when mixed illuminants are discriminated by the first section, they are further tested for a high efficiency source in the second section.
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Eastman Kodak Company
Eisenberg Jason D.
Gonzalez Frank
Woods David M.
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