The Spectral Distribution Chart

UNDERSTANDING THE SPECTRAL DISTRIBUTION CHART

HOW IS LIGHT INTENSITY MEASURED?
The lighting industry measures light intensity in lumens. Lumens represent how intense or bright a light source is to the human eye. A lumen rating does not measure the quality of the spectrum being produced by a light source.

WHAT IS A SPECTRAL DISTRIBUTION CHART?
The spectral distribution chart is a visual representation of the light spectrum produced by a lamp. It is a graph showing the relative intensities of a light source at each wavelength.These charts can be used to compare the energy levels of various light sources. They are the most practical way to compare the quality of light created by different light sources. The chart shows exactly which wavelengths of light (measured in nanometers) the objects are receiving.

HOW TO READ A SPECTRAL DISTRIBUTION CHART?
On the left of the chart is the percent of relative energy. The highest energy output of the light source is plotted as 100% Relative Energy. The 100% peak is used to compare the energy levels of all other wavelengths of light produced by that light source.

The bottom of the chart shows all of the wavelengths of visible light energy that the light source produces. For example, if a wavelength is at 50% relative energy, that peak has half the energy when compared to the 100% peak. Scaling each chart to 100% relative energy allows side by side comparison of light sources with different lumen ratings (intensity) or wattages. For example, a 1000W HPS lamp has more overall intensity than a 400W HPS lamp even though their spectral distribution charts are the same.

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