外光主义(Pleinairism), 又称为露天派或外光派. 意思为直接在日光下作画, 回到画室内亦不会作出任何修改.

起源于印象派画风时期(大约1860年). 当时各地艺术家大多在画室内作画, 苦心追求更多元化色彩的过程却意外发现室外和室内光线对颜色的细微影响. 因此当时不少人大力提倡室外作画, 牵起一股潮流继而自成一派.

其中, 以霍金・索罗亚(Joaquin Sorolla), 文森·威廉·梵高(Vincent Willem van Gogh), 亨利·马蒂斯(Henri Matisse)等著名画家均是外光主意的表表者.

En plein air (French pronunciation: ​[ɑ̃ plɛn ɛːʁ]), or plein air painting, is a phrase borrowed from the French equivalent meaning "open (in full) air". It is particularly used to describe the act of painting outdoors, also called French:peinture sur le motif ("painting of the object(s) or what the eye actually sees"), where a painter reproduces the actual visual conditions seen at the time of the painting. This method contrasts with studio painting or academic rules; those might create a predetermined look. En plein air can also be used to describe other activities where a person partakes in an outdoor environment.