A lux is a unit of illuminance, or luminous flux per unit area, in the International System of Units (SI) . It is equal to one lumen per square meter. In photometry, this is used as a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface. Lux is used to measure the amount of light output in a given area. It enables us to measure the total “amount” of visible light present and the intensity of the illumination on a surface. One lux is equal to the illumination of a one-meter square surface that is one meter away from a single candle. The closer to the light source, the higher the lux reading, and without a sufficient lux level, it can be difficult to read or take good photographs. Common lux levels include dark, cloudy day: 1,000 lux, or 20 micromoles per second per sq meter; indirect daylight: 10,000 lux, or 200 micromoles per second per sq meter; and direct daylight: 100,000 lux, or 2,000 micromoles per second per sq meter.