Plant growth (photosynthesis) is not then determined by lux or energy, but by the photons from the blue to red (400-700 nm) part of the spectrum. This is called growth light! For horticulture, natural daylight (global radiation) is in most cases measured in terms of energy (J orW) with a solar meter. This meter is generally positioned on top of the greenhouse.The value of global radiation is important for climate and humidity control in the greenhouse. Agrolite XT lamps are specially developed for maximum growth light and are among the most efficient light sources available for horticulture