Radiant Imaging (www.radiantimaging.com) makes measurements of the radiance (or luminance) of a source by taking a series of calibrated 16-bit photographs of the source using a high-linearity, low noise camera and combining them into a database. Their ProSource software allows this data to be viewed in many ways and for rays to be generated that represent the full radiance (angular and spatial distributions) of the source.

A demonstration version of ProSource may be downloaded from the Radiant Imaging website. This article models a Luxeon LXLH-BD01 LED, which requires a fully licenced copy of ProSource to use and a license for the particular source model. Therefore, the data files generated in this section are not included for download with this article.

The key benefit in using Radiant Sources is that as the full measured data is available, effects due to reflection, scattering, total internal reflection can be seen. Here for example are photographs of the unilluminated LED and the illuminated LED:

This shows detailed optical effects due to the structure of the source. For example, the contact electrodes partially occlude the reflecting ring, and there is a criss-cross pattern superimposed over the emitting surface. A large number of photographs are taken at different angles and this is used to compute a model of the radiance (or luminance) of the source. Radiant Imaging's ProSource program allows the user to see detailed performance characteristics of the source. Here, for example, is the luminous intensity of a slice in x through the center of the LED:

This is clearly far more detailed than the data originally provided by the LED manufacturer. ProSource can export this data as a source_file, which is a table of rays that ZEMAX can trace:

The ringed settings indicate that:

• We will generate 10 million rays
• The rays will be generated over 2p steradians
• Importance weighting is used, so more rays are generated in brighter regions
• As the LED has a radial aperture of 3 mm, we choose to generare rays initially on a sphere of radius 3 mm

Note that the ray file must be saved in the {zemaxroot}/object folder, and must have the extension .dat.

To use this datafile, change the source_radial to a source_file and open the Radiant_Source.dat. In order to see random rays in the layout plots, set the "Randomize rays" control under System > General > Non-Sequential to 1e+8.

Note this file will require more than 500 MB of free memory. When we trace the rays, the spatial and angular performance of the source is as follows:

Spatial data (Illuminance, in Lux)	Angular Data (Luminous Intensity, in Candela)

This data file is much more richly detailed in both the spatial and angular domains. The spatial results clearly show the "batwing" structure of this source, which is not predicted from the angular data alone. The angular data also shows considerably more structure than the simple curve on the manufacturer's datasheet. Note how the subsidiary structure is faithfully reproduced in the ZEMAX ray-tracing results:

We can also compare the spatial performance. The rays are generated on a sphere of radius 3 mm. If we trace the rays backwards, they will come to a virtual focus, where we can see the image formed. Generating 10 million rays within a cone angle of a few degrees:



and telling ZEMAX to trace these rays backwards:



yields the following spatial distribution at the virtual image:



compare this to the photograph in the ProSource database:



ZEMAX and ProSource use slightly different image gamma, but it can be seen that these images are basically identical. Notice also that if you zoom in on the ZEMAX detector window, two ghost images of the LED emitter can be seen: this is also in the ProSource data:

Note: this is not a photograph! This is the result of a ray-tracing simulation inside ZEMAX. The use of measured radiance data gives extremely accurate source modeling.