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Abstract: The present study examined the critical flicker fusion (CFF) of spectrallights and white light at different luminance levels. Flicker was produced byintercepting a beam of light with a sector disk driven by a variable speedmotor. Six wavelengths were used, i. e. 440, 460, 540, 560, 640 and 660 nm.CFF thresholds were determined with three subjects of normal color vision. The results indicated(1) the relation of CFF to log I or to luminancelevels (Ferry-Porter law), for a given range of luminance, is a linear one,except at the highest luminance level (5087td). White light showed CFFmax and the slope for the curve relating CFF to log I was larger than thatof each of the colored lights. It was shown that luminance is one of the mostimportant determinants for the relation between CFF and log I. (2) Amongcolored lights used, green is higher than those at the extreme ends of thespectrum for either absolute values of CFF or the slope described above.Based on these results, we may infer that the effect of wavelength on therelation between CFF and log I is not negligible. (3) While the differenceof curves described above between middle wavelength and extremes of thespectrum is rather obvious, the difference between the curves of adjacentwavelengths or the same hue is not apparent. It seems that the influence ofwavelength separations on CFF is negligible. (4) Under some luminancelevels absolute values of CFF are lower for white light than those for coloredlights, but the CFF max for white light mentioned is greater than those ofall the wavelengths used under highest luminance levels. Our findings oncemore suggest the reconsideration of the appropriateness of the application ofCIE V(λ) under certain conditions.

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