Measuring Photosynthesis & Consumer Interpretation: PAR, Lumens, PPFD & DLI

Words and images by Richard Jones.

Part 2: Lumens

A lumen is a unit of luminous flux that is derived from lux. One lux equals one lumen per square meter. As is detailed by the following LI-COR LI-210R Photometric Sensor, the Lux Response is heavily weighted to measure peak human sensitivity (555nm), because a lux/lumens measurement is specifically designed to assess the effectiveness of light as it’s perceived by humans. “Lumens are for humans,” which is ideal for testing household, office and public lighting, but it’s a limited gauge for assessing the intensity of horticulture lights.

Blog 01 Chlorophyll a b Compared to Lux 02.2

Consumer Interpretation of Lumens

Although lumens primarily measures the intensity of Green and Yellow light, it’s possible to glean a couple obvious conclusions:

  • Lumens provides an effective way of assessing which grow light emits a wider bandwidth and has the associated capacity to stimulate Anthocyanin, Phycoerythrin and Phycocyanin.
  • Lumens may also indicate which grow light emits more Green light and has the associated capacity to stimulate shady areas of a crop.

In order to provide context for assessing the significance of lumens, access to the corresponding grow light spectrum is required. For example, a grow light that boasts of high lumens, may have an inefficient spectrum if most of its light is focused from 500 to 600nm. An excessive amount of Green and Yellow light may enhance the growth of ferns, but could limit the development of flowering/fruiting/nectar-producing plants. Fruiting plants typically perform best in an environment that’s dominated by Flowering light (600 to 700nm). Therefore, a high lumens value can be associated with an inferior grow light.

In contrast, the ZenPro 400plus emits 12,000 lumens and a full-spectrum in which Orange and Red light are dominant. In this example, the high lumens value is an indication of a strong Green and Yellow signature, but within a well balanced spectrum.

ZenPro 400plus w Spectrum 02.1

Part 3 explores PPFD.

Happy growing from Zenith LED Grow Lights.

Words and images by Richard Jones.

Copyright © 2016   Zenith LED Grow Lights & ActionGroove Media Limited.

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