I recently watched a very informative video on Practically Tactical's Youtube page about light. It can be found at https://www.youtube.com/watch?v=nHEpWNqdeLc. Nick From Practically Tactical hosted Matt from Cloud Defensive. Matt went on to explain what role lumens play and the role that candelas play in a light's performance. He explained the two components in an way that is easy to understand and then later further elaborated on specifics. Lumens is the amount of light being transmitted from an object. Candela is how concentrated the light is into a smaller area. This means the higher the Candela, the more concentrated the light's path. This is why handgun lights have lower Candela. Handguns are meant to be used at shorter range therefore it is more important to have more spill in order to illuminate the room or the close range threat. Spill is a term to describe light that is less concentrated. This means the lower the Candela, the greater the spill. Lights that are put onto rifles should have a higher Candela rating in order to use the rifle to it's ability of reaching farther targets. One can only shoot effectively and safely as far as they can see. If the rifle is intended to be used for farther distance one should put a rifle light on the rifle instead of a pistol light that has a lot of spill and will limit the rifles range. With Matt and Nick talking about both of these applications I can see how it is important to choose the correct light for the mission one is trying to accomplish. Matt also explains how different color lights can penetrate objects such as fog, smoke, rain, etc. This is why fog lights on vehicles are yellow, it will penetrate through these environmental barriers whereas both low and high beams will not. They both covered many aspects of low-light environments and they explained the factors in a way that was very easy to understand. If you find yourself with a half hour to spare, I recommend checking this video out.