Understanding Spectral Plots

[Laddy]

Can anyone explain what exactly I'm looking at here? I've seen these charts for years, and to be honest, I've never understood what I'm looking at, or what data can be deduced from them.

Taken from Sanjays Manhattan Reef site:

Any help from the lighting guys on this would be much appreciated.

 

[jtma508]

These are produced using a spectroradiometer as opposed to a PAR meter. The spectroradiometer scans the light spectrum (in your example from UV-A (400nm) up to near-infrared (~700nm). This happens to be the PAR sepectrum. The graph shows the spectral output of the tested light source. In your example, most of the light is around 450nm (deep blue) with minor peaks in the green, yellow and far-red regions. Looks like a 20k bulb. Your plot displays the output in watts per square meter, others (e.g., LEDs) use relative output which shows the output of all wavelengths relative to the dominant wavelength. So, the x-axis shows color (violet on the left and deep red on the right) and the y-axis shows the amount of output of the light source.