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Measuring Plant Lighting

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There are a number of ways to measure indoor plant lighting levels. As such, there remains considerable

debate as to which method provides the gardener with the best information in determining if the light source is

providing the ideal wavelengths and intensities to optimize plant response. While the debate swirls it ultimately

will always come down to our plant‟s response to those spectrum and intensities.

We recognize that the complexities of understanding and choosing which technology, or lamp, is best suited

for gardening with indoor artificial lighting can be confusing. We publish our lamp‟s output data in a format that

you may not be familiar with, but we believe it offers the gardener a better opportunity to determine how much

energy a lamp emits between 400-700 nm relative to generally accepted photosynthetic absorption regions.


As you can see by this Net Action Absorption Chart, what is believed to be the areas of greatest importance for a lamp‟s energy to meet peak chlorophyll absorption points would be in the Vegetative Regions (Ultraviolet-Blue) and Flowering.

Regions (Red-Far Red). Less energy is required of the Carotenoid region (Green-Yellow) but as you can see there 

is still need for the lamp to emit within this region.

Grow lamp manufacturers produce Spectral Distribution Graphs for their lamps that graphically depict where

the lamp will output wavelengths and in what intensities those wavelengths will emit. This works well in

allowing the consumer to determine the lamps spectral output characteristics. The gardener can then decide if

that particular lamp would work best for the type of plant being grown, specific growth cycles or if the spectrum

is broad enough to take the plants from a vegetative thru a flowering state utilizing a single lamp.

In determining the proper lamp to purchase, the gardener will sometimes mistakenly rely on numerically driven

data such as a comparison of lumen output, lumen/watt, kelvin, lux, and μmole ratings to name a few. For

plant lighting comparisons, each of these values will at best give incomplete information and at its worse, will

provide you with information that is mostly irrelevant to what your plants actually require from the lamp.

A more informed approach relies on a review of the manufacturer‟s spectral distribution graph. Once installed,

the gardener will still want to measure light intensity to have complete lamp performance data. These types of

field intensity measurements are usually made with a modestly priced PAR meter which has been calibrated to

the sun and not the artificial light source being measured.

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