A photovoltaic effect and photoconductivity, each with its own spectral response curve, occur simultaneously in a β-carotene cell. The two effects produce currents in opposite directions and with different response times. The combination of these effects imparts to the total response curve a unique shape for each region of the visible spectrum. Blue light produces a monophasic, negative deflection; red light produces a monophasic positive deflection; and intermediate wavelengths produce diphasic responses, which are mixtures of these two. The relative amount of each component depends upon wavelength.
The shapes of these response curves are in detailed agreement with the chromatic “S” potentials found in the retinas of some animals. These results suggest a physical basis for these biological responses. The action spectra for these curves are of the same general nature as the chromatic functions of the Hering opponent-processes theory in vision This suggests that two such cells as these (a red–green, and blue–yellow type) in conjunction with a black–white detector, would suffice to account for all color mixing data, and thus form a new basis for objective colorimetry.
Mixtures of light of longer and shorter wavelengths simulate the response to any monochromatic light. Broadband light of a given color produces the same character of response as a monochromatic beam of a similar color. The response curves for a given color are fairly stable with a tenfold change of irradiance The balance (or neutral) point at a wavelength where the opposing currents are equal, is a function of the voltage applied to the cell; it shifts to shorter wavelengths as the voltage increases. A primitive type of color matching can be accomplished with a single cell.
© 1964 Optical Society of AmericaFull Article | PDF Article
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