EMR Spectrum

T his page is dedicated to a much deeper look into Electromagnetic Radiation (EMR) spectrum and the Ultraviolet (UV) Index as in relation to lighting sources. The UV Index is an international standard measurement of the strength of sunburn-producing UV radiation at a particular place and time. The scale was developed by Canadian scientists in 1992, then adopted and standardized by the UN's World Health Organization and World Meteorological Organization in 1994. The UV Index is designed as an open-ended linear scale, directly proportional to the intensity of UV radiation that causes sunburn on human skin. The purpose of the UV Index is to help people effectively protect themselves from UV radiation, which in excess, causes sunburn, skin aging, DNA damage, skin cancer, immunosuppression, and eye damage.http://www.who.int/uv/intersunprogramme/activities/uv_index/en/index2.html

The UV Index is a number linearly related to the intensity of sunburn-producing UV radiation at a given point on the earth's surface. It cannot be simply related to the irradiance (measured in W/m2) because the UV of greatest concern occupies a spectrum of wavelength from 295 to 325 nm. Skin damage from sunburn, however, is related to wavelength, the shorter wavelengths being much more damaging. The UV power spectrum (expressed as Watts per square metre per nanometre of wavelength) is therefore multiplied by a weighting curve known as the erythemal action spectrum, and the result integrated over the whole spectrum. This gave Canadian scientists a weighted figure (sometimes called Diffey-weighted UV irradiance, or DUV, or erythemal dose rate) typically around 250 mW/m2 in midday summer sunlight. So, they arbitrarily divided by 25 mW/m2 to generate a convenient index value, essentially a scale of 0 to 11+ (though ozone depletion is now resulting in higher values).https://serc.si.edu/labs/photobiology/UVIndex_calculation.aspx , https://www.epa.gov/sunsafety

UV Region

Visible Light Region

Infrared Region

Light Spectrum from Grow Lights

Compact Florescent Lightbulb (CFL)

Metal Halide (MH)

High Pressure Sodium (HPS)


Light-Emitting Diode (LED)

*All charts used for light sources (LED, CFL, MH, Plasma and HPS) are merely examples of common styles of grow lights. These are not definitive representations for each category, nor do they represent all available grow lights.