In light, frequency refers to the number of times a wave repeats itself in one second. Frequency is commonly measured in hertz (Hz), which is equivalent to the number of cycles per second. Different types of lighting sources have different frequencies, which can affect how they appear when used for illumination or color-rendering purposes. For example, incandescent light bulbs usually have higher frequencies than fluorescent lights. Higher frequencies tend to enable more accurate color rendering and better contrast levels.