Spectral Power Distribution, the radiant power of a source plotted against wavelength, usually from 380 to 780 nm. It is the fundamental description of a light source: CCT, CRI, TM-30, melanopic values and lumens are all calculated from it. A typical white LED shows a sharp blue peak near 450 nm from the chip and a broad phosphor hump through green, yellow and red; incandescent is a smooth rising curve.
Send me the SPD, not just the CRI, I want to see how deep that red end goes before we approve it for the museum.
Also heard as
- spectral power distribution
- spectrum
- spectral distribution
Related terms
Spectroradiometer
An instrument that measures light's power at each wavelength, from which color and photometric values are calculated.
CRI
Color Rendering Index: a score up to 100 for how true surface colors look under a source compared with a reference light.
Metamerism
The effect where two colors match under one light source but not under another, because their spectra differ.
Melanopic EDI
Melanopic Equivalent Daylight Illuminance: a measure, in lux, of how strongly light stimulates the eye's circadian system.
Radiometry
Measurement of optical radiation in physical energy units such as watts, without weighting for human vision.