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 used for plant growth. 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 plants are receiving (see example below).

BLUE Metal Halide Spectral Range

Reading 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 makes it easier to do a side-by-side comparison of light sources with different intensities and wattages. For example, a 1000W metal halide lamp has more overall intensity than a 400W metal halide lamp even though their spectral distribution charts are the same.

Furthermore, a 1000W EYE HORTILUX BLUE has less intensity and a more balanced spectrum when compared to a 1000W EYE HORTILUX Metal Halide with more intensity.