La resa cromatica di una fonte di luce descrive la capacità di tale fonte di rendere in modo accurato i colori degli oggetti percepiti, persone e cose. Come regola generale, più elevato risulta l'indice IRC della fonte di luce e migliori appariranno gli elementi illuminati dalla lampada.

SP lamps have a CRI of 70+ making them better color rendering light sources than older standard fluorescent lamps. SPX lamps have a CRI of 80+ even better than SP lamps, an even higher color rendering with the same high efficiency. A second consideration in light source selection is the degree of visual "coolness" or "warmth" of the light source.

GE SP30 and SPX30 lamps produce a warm appearance slightly enhancing reds and yellows. SP35 and SPX35 lamps produce a balanced tone, midway between warm and cool. SP41 and SPX41 lamps are cooler in tone, slightly biased toward blues and greens. SPX50 is a very cool, high color rendering light source designed to simulate natural outdoor daylight at high efficiency. SP65 and SPX65 lamps also provide very cool light similar to the north sky and are considered an ideal substitute for daylight color lamps.