照度（英语：Illuminance）是每单位面积所接收到的光通量。SI制单位是勒克斯（lx=lux）或辐透（ph=phot），1勒克斯=1流明/平方米，1辐透=1流明/平方厘米，1lx=0.0001ph。

居家的一般照度建议在100~300勒克斯之间。对于同样光源而言，当光源的距离为原先的两倍时，照度减为原先的四分之一，呈平方反比关系。

一些日常的代表性照度：

In photometry, illuminance is the total luminous flux incident on a surface, per unit area. It is a measure of how much the incident light illuminates the surface, wavelength-weighted by the luminosity function to correlate with human brightness pe****tion. Similarly, luminous emittance is the luminous flux per unit area emitted from a surface. Luminous emittance is also known as luminous exitance.