To provide selected illumination in the near infrared spectrum the SL1 needs IR-filters which do suppress the visible light and which allow the IR-spectrum to pass. IR-filters are usually built on principles of absorption or interference.

Absorption-filters (left) consist of tainted glasses which allow light of a certain spectrum to pass through. Interference filter (right) rely on mirrors with reflective material that do capture some spectral bands and transmit others.

 

Absorption-filters (AF) are less selective than interference-filters (IF). The filter curves of the AF are less steep than those of IF – a clear indication that some visible light can pass through the AF while the IF can cut-off most of the visible light.

To achieve a long distance illumination some of the red spectrum can be useful. Swisslicht offers different options of filters designed to work with SL1; others are in development.

Usually a long range illumination goes with some visible red glow. However, the parabolic mirror of the SL1 limits the red glow to a very narrow angle of reflection along the line of sight. Few degrees away from the line of sight the red glow is disappearing rapidly.

AF800 is an absorption-filter with a high transparency starting at 800nm. Combined with the SL1 it offers an extreme long range of IR-illumination up to 1500m. It is transparent for some of the visible red spectrum supporting night vision equipment with image amplifier tubes. Status: available

A detailed documentation explains the technical and optical interrelationship between light source, filter, night vision equipment and eyes. We can support you in defining a proper nighgt vision solution.

Technical Documentation Night Vision Solutions (5 pages A4)