This is a replacement for the 2mm thick water-free vitreous silica glass detachable filter that is supplied with the Smart Q Infrared sensor. This filter will allow visible and near infrared to pass i.e. 0.15 microns (155nm) to 4 microns (4000nm), but will block out mid and far infrared. When this filter is fitted the sensitivity of the Sensor will be restricted from 0.23 microns to 4 microns