Modeling sources in TracePro to obtain valid near-field analysis results

Synopsis

Modeling sources in TracePro to obtain valid near-field analysis results

Symptoms

Some methods for modeling sources treat the source as if it was a point source. This will provide accurate results in the far-field, but will not be adequate for near-field applications where there is geometry close enough to the source that the rays starting locations are critical.

Solution

Here is a summary of the TracePro source options and their limitations. The four source types are:

1. Grid Source
2. Surface Source
3. File Source
4. Image Source

1- The Grid Source does not provide any useful options for near-field analysis for an LED

2A - A full up CAD model of an LED, with a Lambertian emitting Surface Source applied to the surface of the LED Die, will provide good near-field analysis results in TracePro. The challenge here is that you need an accurate CAD model of the LED, and you need accurate property data. The manufacturers are not typically willing to provide this info. You are more than welcome to try to get it. If the data does not come from the manufacturer, the other option is to reverse engineer the LED and accept the risk of errors in that process.

2B - A Surface Source can also be used in the mode of creating a simple Block or Cylinder in TracePro to represent the LED, then apply a Surface Source Property (select Define/Edit Property Data/Surface Source Properties). TracePro comes with 10 or 12 catalogs of data. However, these provide valid far field results, but the near field is not valid. TracePro will randomly select locations on the surface of the Block or Cylinder for the starting locations of the rays, and also randomly select an angular direction for the ray. But the angular direction is not correlated to the ray starting point. So the data is only valid in the far field.

3A - A File Source generated from an IES file cannot be valid in the near field, because the IES file did not include near field data in the first place

3B - In general, the concept of a Source File in TracePro can provide valid near-field data. The Source File specifically defines the start location and angle for each ray. One source of valid near field data is Radiant Imaging, they are in the business of measuring sources. They sell a software program named ProSource that takes ProSource files and converts them to TracePro Source File format. So one option is to purchase ProSource and get a copy of their data file for your LED. However, many of the LED manufacturers have struck a deal with Radiant Imaging, and now post the Source Files on their website. So this is the best option if it is available. For example, if you scroll down this webpage, then select Design Resources/Optical, you will find a set of TracePro Source Files available for download:

LUXEON Rebel White LEDs

The only downside of the Source File approach is that you do not have any CAD representation of the LED in your TracePro model. If you wanted to analyze the effects of rays that emit from the LED, hit other surfaces, then bounce back off the LED structure, you still need a CAD model of the LED.

4 - Image Source - An image source provides another way to make a spatially-varying light source in TracePro. Angular distributions for Image Sources are limited to Uniform, Lambertian and Gaussian, but Lambertian is a good approximation for most bare LEDs. To use this effectively, you will need an emitted irradiance map at the surface of the LED, made into in image file (bmp, jpg, png, etc.) to use as an Image Source in TracePro.

In summary, the approaches that are adequate for near-field analysis are:

2A - A CAD model either from the manufacturer or by reverse-engineering

3B1 - purchase ProSource from Radiant Imaging

3B2 - download TracePro source files from LED manufacturers' websites.

4 - An Image Source made from the irradiance map of a bare LED.