dispersive power

Dispersive power in optics refers to a transparent material's ability to separate different colors of light through refraction. This occurs because the speed of light in a medium depends on its wavelength, causing different colors to bend at slightly different angles.12

The dispersive power is quantified by comparing the material's refractive index for different wavelengths. Specifically, it's often measured by the difference in refractive indices for blue and red light (like the F and C lines of hydrogen), divided by the refractive index for an intermediate color (like the D line of sodium). A higher dispersive power means a greater separation of colors. This phenomenon is responsible for effects like rainbows, where sunlight is dispersed into its constituent colors by raindrops.132