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Growers generally have two options when it comes to horticultural LED spectrums – “full spectrum” or “broad-spectrum”, which appears as white light; and “red/blue spectrum”, which can appear as purple or pink light.
The red/blue spectrum LED luminaires are often referred to as narrow band spectrum lights – because the wavelengths they emit are within a narrow band of light. LED luminaires that emit a “white” light are often referred to as “broad spectrum” or “full spectrum” lights because they include a broad band of the light spectrum (more similar to the sun) which renders a “white” light (there are no true white wavelengths).
It should be noted that essentially all “white” LEDs are blue LEDs that are coated in a phosphor that converts the blue light into longer wavelengths. The phosphor absorbs the blue light and re-emits some or most of the photons into green and red light. This coating reduces the efficiency of the LED in converting photons into usable PAR (photosynthetically active radiation) light, but makes for a better work environment in sole source applications. The composition of the phosphor coating will help to determine the spectral quality of the white light emitted. To find the efficacy of your luminaire, you will need to divide the Photosynthetic Photon Flux (PPF) of the luminaire, by its input wattage. The resulting efficacy value, will be represented in μmol/J. The higher the number, the more efficient the luminaire is at converting electrical energy into photons of PAR.