Understanding Spectrum, Lumens, PAR and PPFD

Guides

January 11, 2017

Both vision and plant growth are completely dependent on light, however, the way our eyes react to light and the way plants depend on it are entirely different processes.

Lumens- You may see lumens listed on various lighting fixtures, including grow lights. Lumens are the measurement of visible light emitted from the light source. Generally, the brighter a light source appears, the higher the lumen output of that source will be. So lumens are a good measurement to use when trying to determine how to light a room, but as far as your plants are concerned, lumens do not matter. Lumens do not tell us how well plants will respond to visible light.

PAR and Visible Light Spectrum- The spectrum of light that is visible to the human eye is approximately 380-780 nm (nanometers). Interestingly, plants also use almost the same spectrum of light visible to the human eye. This part of the electromagnetic radiation, which powers photosynthesis, is named PAR (Photosynthetically Active Radiation) and is usually found in wavelengths from 400 to 700nm. PAR is often confused as a type of measurement, but is more the designation of a region of light within the spectrum that is usable to plants.

PPDF- (Photosynthetic Photon Flux Density) is a measurement that is very important to your plants. Unlike lumens which will only measure the brightness of a light source, PPFD measures the number of photons within the PAR region that reach the target each second. Simply put, a PPFD measurement will tell you how much necessary light (within the PAR region 400-700nm) is actually making it to your plant.

Applying to plant growth- As discussed, plants use light within the spectrum of 400-700nm. However, certain areas of that spectrum are much more useful than others. Keeping things simple, light from the blue end of the spectrum (around the 440-470nm range) is necessary for vegetative growth – making for strong, healthy plants with thick foliage. In contrast, red light (around the 640-660nm range) is necessary for flowering and fruiting – producing large, dense buds along all of the nodes that were created, in part, by the blue lights.

Perfecting your Lighting- Less efficient forms of grow lighting, such as metal halide and high pressure sodium, will deliver the necessary type of light to your plants, but it does so in a very inefficient way. Using massive amounts of power these light sources basically throw all colors of the visible light spectrum at your plants, including the ranges that your plant can’t even use.

Cultivate Tech fixtures are FULL-CYCLE LED grow lights designed to maximize efficiency by only targeting the spectrum of light your plants need to thrive during the different grow cycles it will go through. Using separate dimmers for the red and blue ends of the spectrum, the grower is in full control of what type of light their plant is getting and when. During the vegetative stage, more blue can be used with red still present, but toned down. When the grower has decided to trigger the flowering stage in their plant, they can slowly introduce more red, while turning down the blue end of the spectrum. Rather than abruptly changing light sources to accommodate your plants changing needs in it’s different grow cycles, the gradual fine tuning of Cultivate Tech fixtures closer mimics the natural phases of sunlight as it passes from summer to winter.