Lumens are for Humans

There’s a saying in the growers community that “Lumens are for humans, but PAR is for plants.” What they mean by this is that humans need light to see, and plants need to absorb light as energy in order to grow. Many colours of light that the human eye is most sensitive to is used least by plants, and vice versa. It is vital to understand this key difference when considering color spectrums and growth for your plants.

So how do we measure light for plants? 

Lumens and PAR (Photosynthetically Active Radiation) are both measurements of light, but are measuring light in different ways. Humans use light to see, and we can see some colours of light better than others or not at all (like Ultraviolet or UV). Plants use light to absorb energy (in the form of photons) as part of their growth cycles from vegetative to flower states. Different colours of light are better for growth than others and specific combinations can be achieved for optimal results.

Light can be characterized in other ways when considering its benefit to plants. Colour temperature is often referred to in the horticultural industry on luminaires to best describe the color of the light emitted by the lamp. Colour temperature is listed in Kelvin (K), which is a measurement of temperature. This certainly characterises the color of light as we perceive it, however the color temperature metric fails to address how effective a particular light source will be at generating the energy necessary to drive photosynthesis.

So how do plants absorb light?

Plants absorb light needed for growth by stimulating photosynthetic pigments known as Chlorophyll.  More specifically, Chlorophyll A, Chlorophyll B and Beta Carotene. These pigments respond better to different light colours. In general they respond better to blue and red light.

Chlorophyll A is a specific form of chlorophyll used in oxygenic photosynthesis. It absorbs most energy from wavelengths of violet-blue. Chlorophyll B is the accessory pigment that collects energy and passes it on to Chlorophyll A. This pigment absorbs red light the best, and converts the light into energy that it uses for metabolism.

So what does all this mean? 

By avoiding redundant wavelengths, your plants will require less energy to deliver far greater yields per watt, and only quality LED technology can deliver this performance.

In short:

Blue / red light → chlorophyll A/B growth stage in photosynthesis = optimal plant growth

When combining a specialised mix of blue and red colors on a blended spectrum luminaire chip, we get a visible purple color which we have adopted as the perfect grow light in our FUSION series.  

In summary, lumens and kelvin are not an accurate descriptor of your grow light’s ability to drive photosynthesis. We must consider other factors such as PAR (Photosynthetic Active Radiation) and  Photosynthetic Photon Flux Density or PPFD

For more info about what drive’s plant growth, see our article which describes: What is PPFD?

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