The light that reflects out of a diamond can appear in brilliant white flashes, or in a rainbow of color, referred to as fire. The fire effect is caused by the proper bending and dispersion of light as it travels through the diamond. The more colorless the diamond, the truer the dispersed colors will appear.

Observable fire is increased in a slightly darker room when there are fewer light sources (such as a candle light). Conversely, scintillation is maximized in strongly lit areas (such as an office). Fire and scintillation are simultaneously maximized by very strong, pinpointed light sources (such as the spot lights prevalent in jewelry showrooms).

Maximum brilliance is achieved in diamonds that posses both fire and scintillation.