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Lumens are for Humans

Tuesday, 1 November 2016  | 

For decades now growers have been obsessed with the lumen output of their lamps, misguidedly thinking that the more lumens then the better the light is for the plant. Lumens is how we started to measure light back in the day and is a measurement by its availability to the human eye curve and is the industry standard way of measuring any lamp.

Plants do not even recognize what a lumen is, but instead rely on photons hitting the surface of the leaf to make them grow, these photons we call PAR (Photosynthetically active radiation). PAR is measured in micromoles (μmol m-2 s-1) and is basically a count of the photons hitting a surface that are available for use by the plant.

 
The Human Eye Curve

Light generates a photochemical reaction. In human eyes it is reacting with the photo receptor in different versions S, M and L. In plants, the light is reacting with Chlorophyll a and b.

Humans are only able to perceive a tiny portion of the full electromagnetic spectrum and this differs greatly to what is available to our plants and other species, for example birds of prey have evolved to have some degree of UV vision to help them more easily track their prey.

Human Eye Curve
Plant Absorption
The electromagnetic spectrum