LED are important in different fields of architectural illumination, for lighting fixtures and for the automotive industry. To get photometric data of the LED, a well adaptable measuring system is necessary. It must be able to capture high dynamic images for different areas of color spaces as well as for different light intensities and luminances.

Moreover, it must be possible to determine intensity gradients and also the uniformity of light sources for both assemblies and Single-LED symbols.
All this information can be determined by means of an imaging photometer or imaging colorimeter within fractions of a second. In addition, there are image-processing operations specially adapted to these problems.

Depending on the specific application a LED can be measured either directly or indirectly. The measuring principle for the indirect measurement is shown in the following figure.

As can be seen in the image above a diffusing screen is mounted at a suitable distance to the LED assembly. The luminance and chromaticity coordinates can then be measured on this screen.
There are applications just as emergency exit lights, where especially the single results of each LED compared with one another are of interest. So, it has to be checked whether all LED have a minimum of intensity (luminance) and also that the color distance between the LED is within a pre-defined tolerance