Photo-Reactive Armor

Photo-Reactive Armor was a technology in development by the High Guard before the Fall. This was picked up by the Knights of Genetic Purity, which improved the technology over the Long Night. Eventually, the Genite Photo-Reactive Armor could withstand almost all known types of small arms. The Force Lance was one of the few personal weapons able to penetrate the armor. Thanks to the armor, small Genite strike teams were capable of engaging much larger forces. Nietzscheans, armed traditionally with Gauss weapons, were especially vulnerable as their weapons were almost completely ineffective.

The name suggests that the armor uses light in order to nullify the kinetic energy of whatever hits it. Conventional reactive armor works by blasting out a piece of outer armor to counter the kinetic energy of an incoming projectile. This outer armor is likely replaced with light, which means as long as there is energy, the armor will continue to deflect incoming fire. However, there probably exists an upper limit of how much the light can nullify before the armor itself starts taking hits.