When should I use an IR cut filter and when should I use heat absorbing glass?

The decision is usually based upon the application. An IR (infrared) cut filter will reflect the IR and pass the visible wavelengths. These filters can generally be made very thin due to the fact that the filtering effect is created by a thin film coating and not the glass. The main drawback is that they are angularly dependent. With heat absorbing glass, the near IR wavelengths are absorbed by the glass and cause the glass to increase in temperature. For this reason the filter needs to be thicker and a way to evacuate the heat is required. Due to the high potential for damaging the filters with excessive heat, we always recommend using plenty of air space, apply heat sinks, select tempered glass when available, and use forced air-cooling as required. We suggest for first time configurations to monitor the heat situation closely to avoid damage to any optics. If components get excessively hot over a short period of time, they will eventually crack.