What unit is used to measure the frequency of visible light? The unit used to measure the frequency of light is the hertz. The frequency of visible light corresponds to a band of frequencies in the vicinity of 430â€“770 terahertz (THz)! There are a trillion (1,000,000,000,000) terahertz in a hertz! Post navigationPrevious post: Which colour of visible light has the higher frequency, red or violet?Next post: What type of electromagnetic radiation has the highest frequency?