C Daylight(TM) glasses are designed to convert light from domestic incandescent lamps (approximate to Illuminant A) to the Illuminant C phase of daylight. The efJicacy of this conversion is quantified here far the Farnsworth D15 test. Spectral transmittance and reflectance data for the filter and D15 caps, respectively, are used to compute chromaticities of the caps under illuminants C, A, and the filtered illuminant SA. The chromaticities of A and fA deviate from C by 13 JNDs and 1.6 JNDs, respectively and, similarly disparate shifts occur for the 15 caps. After allowing for von Kries adaptation, the chromatic spacing between some adjacent caps approaches I JND for Illuminant A, but is less than 0.1 JND for fA, It is concluded that the color conversion is efficient, (C) 2000 John Wiley & Sons, Inc.