Optical Filter Orientation

One of the most common questions regarding optical filters is in regards to the filter orientation, specifically: which side of the filter should be facing the input light source? For any application, filters should be oriented such that the coated surface faces the light source.

On the opposing surface to the coated surface, an anti-reflective (AR) coating is applied to improve transmission in the desired wavelength range, while adding extended spectral blocking outside of the desired range.

For extremely sensitive applications, proper orientation and directionality should be maintained. However, TECHSPEC^® Filters will perform to specification when oriented in either direction.

Specifying Edmund Optics^® Filters

All mounted TECHSPEC^® Optical Filters have an arrow on the side of the mount that points to the filter-coated surface for quick reference.
All unmounted TECHSPEC^® Optical Filters have a small pencil or ink mark on the edge outside of the clear aperture to indicate the filter-coated surface.