This is the most advanced mil-spec replacement LEDs available for 3v PSO and POSP rifle scopes which use modern 3V batteries (or if you are using a POSP or PSO CR123 battery adapter). These replacement LEDs were designed at one of the most prestigious engineering bureaus in Russia to replace original bulbs so they completely resemble bulb' dimensions. The design bureau boasts a Nobel Prize winner who had a hand in the theoretical blueprint for this new diode design. The average bulb operates at 650 nm while these are at a superior 625 nm. This is significantly better for your eyes. Additionally these are much longer lasting as the element length is compact and therefore less open to disturbance during discharge. This is the standard replacement LEDs for the red or yellow bulbs that come with the PSO scopes however this is a better LED than what was issued with your scope. If you are looking for the best light source for PSO scope on the market, this is it.