Information

Spectral Power Distribution (SPD) Curves

For more information about the project in general contact Joseph Padfield.

Measuring and working with different light sources within the National Gallery:

Comparing Spectral Power Distribution (SPD) curves

This web site has been set up to allow users to examine and compare the Spectral Power Distribution (SPD) curves of a number of different light sources and begin to discuss the relative proportions of these SPDs. The curves and relative proportions can been seen here and here or acessed via the appropriate links at the top of the page. If you would like to contribute data to this project or would like to recommend other sources of information please contact Joseph Padfield.


Further details, including descriptions of the equipment and calculations used, along with additional links can be found on the information page.


Measuring light levels in museums and galleries

Many of the materials used to make up works of art can degrade over time as a result of exposure to light, but we need this light to be able to actually see them. A balance must therefore be established between ensuring there is enough light for people to see, while minimising any long term degradation. Within museums and galleries these light, or Lux levels have been monitored and recorded for many years. Lux levels represent a measure of the brightness, of a given light, as perceived by the human eye, but it does not establish the colour quality of a light, or accurately record the intensity of the light that the human eye is less sensitive to. When examining a single type of light source, for example tungsten halogen, Lux levels allow for a good comparison, however when many different types of light need to be compared then it is better to considered the entire range of light produced or the SPD.


What is the Spectral Power Distribution (SPD) of a light?

"In color science and radiometry, a spectral power distribution (SPD) describes the power per unit area per unit wavelength of an illumination (radiant exitance), or more generally, the per-wavelength contribution to any radiometric quantity (radiant energy, radiant flux, radiant intensity, radiance, irradiance, radiant exitance, or radiosity)." Wikipedia


Example SPDs

Example spectral power distribution (SPD) curves, standard tungsten, filtered daylight and a LED based source.