輻透

輻透（英文phot，符號ph）是光度學所用的照度單位，也就是單位面積內通過的光通量。

輻透並不是國際單位制的標準單位，而是舊式CGS單位制的單位。名詞phot是André Blondel在1921年創造的^[1]。

在公制單位中：

1\ \mathrm {phot} =1\ {\frac {\mathrm {lumen} }{\mathrm {centimeter} ^{2}}}=10,000\ {\frac {\mathrm {lumens} }{\mathrm {meter} ^{2}}}=10,000\ \mathrm {lux} =10\ \mathrm {kilolux}

公制量綱：

照度 = 發光強度 × 立體角 / 長度²

另見

^ Parry Moon. "System of photometer concepts", in the Journal of the Optical Society of America, volume 32, number 6 (June 1942). – Page 355: "The lumen was proposed by Blondel in 1894 and is now universally accepted. The names, phot and stilb were likewise coined by Blondel (1921) and are in general use on the Continent."