The effect of illuminants with different correlated color temperatures on color discrimination ability was investigated by asking 20 color normal observers to perform FM-100 test under D65, TL84, and F illuminants. The experimental results show that the TESs (Total Error Scores) under D65 and TL84 were not significantly different between them, but they were significantly lower than the TES under F illuminant; for F illuminant, the PES (Partial Error Score) along blue-yellow axis was much higher than that along red-green axis. The results indicate that in FM-100 test F illuminant cannot be used as a lighting source, because the color discrimination ability, in particular blue-yellow color discrimination ability, is much reduced under this illuminant.