LED Collimators

Efficient beam shaping in general requires fairly well-collimated illumination.

If the LED is not collimated the LightShaper™ is still able to homogenize and clean up artifacts generally seen in LED illumination.

To produce custom light distributions a good rule of thumb is that the collimation of the source be 4-10x narrower than the nominal angular spread of the LightShaper™. For instance, if the nominal spread of the diffuser is 30 degrees full angle, the degree of collimation of the LED source should be somewhere in the range of 8-3 degrees or less.

Let’s say one wants to illuminate a square area. The better the degree of collimation of the source the sharper will be the edge definition of the square area.

These examples show a diffuser illuminated by laser light and illustrate the effect on the beam shaping. The same principles apply to LED illumination.

Image of a square diffuser with collimated laser light. The square shape is well-defined.

Image of a square diffuser with divergent laser light. The square starts to round and lose sharpness.

LED sources are generally Lambertian, that is, they spread over the full hemisphere with light rays going in all directions. For this type of source diffusers can still be used for homogenization but are ineffective when it comes to beam shaping.

It is necessary to first collect the LED light and then collimate it. Because of the wide angles produced by a Lambertian source simple lenses are not very efficient and we need to use specially designed collimators.

An example of a collimator designed at RPC Photonics is shown below. The collimator dimensions with respect to the LED size determine the degree of collimation. As the height H increases the collimation improves.

For a specific application, one needs a good understanding of packaging constraints and performance targets so the best compromise between size and performance is found.

Once the LED is collimated, the situation becomes similar to having a collimated source coming from the top of the collimator. Some possible configurations are shown below.

Collimator and diffuser as separate components. Diffuser surface faces collimator.

Collimator and diffuser as separate components. Diffuser surface faces away from collimator.

Injection-molded monolithic collimator-diffuser component.

The collimator concept can be extended to include arrays of LEDs to produce luminaires for general illumination with controlled light distribution for efficient lighting applications.