Light Unit Conversion Table

UNIT OF MEASURE	TYPE OF MEASURE	MAINLY USED BY	SUNLIGHT	HPS	METAL HALIDE
Footcandles	Visible (human eye)	Industry (US)	1	1	1
LUX	Visible (human eye)	Industry (Europe)	10.76	10.76	10.76
umol.m^.2s¹ of PAR	Quanta of light in PAR range	Horticulture research	0.02	0.013	0.015
moles/day (PAR)	“daily light integral”: accumulated PAR light during an entire day	Horticulture research x hours of light	footcandle x 0.00071 x hours of light	footcandle x 0.00047 x hours of light	footcandle x 0.00054
Watts/m^.2 (total energy)	Total energy	Engineers, research1	0.101	0.074	0.089

The Light Unit Conversion Table compares units so that you can make conversions to units with which you are familiar. The horticultural industry measure light in micromoles. This measure of visible light (i.e., light visible to the human eye) does not exactly correspond to the spectrum of light energy used by plants in photosynthesis (the range of 400 to 700 nm wavelengths, termed “photosynthetically active radiation or PAR”)

Term	Definition
Lumen:	A measure of light given off by a source. One lumen equals the amount of light emitted by one candle that falls on one square foot of surface located one foot from the candle.
Footcandle:	A measure of radiant light from a standard candle that falls on one square foot of surface area at a distance of one foot.
LUX:	A measure of radiant light from a standard candle that falls on one square meter of surface area one meter from the source.
Micromole:	One micromol per square meter per second (umol.m^.2s¹). A unit of measure of the amount of light hitting a surface that is in the range of 400-700 nanometers.
WM^.2:	Watts per square meter (WM^.2). A unit of measure of the amount of light energy hitting a surface that is in the range of 400-800 nanometers.