Gear Locker: Understanding Lumens in a Tactical/Fighting Flashlight

All you ‘gear geeks’ gather around, This is the best article yet in understanding the in’s, out’s and in-between’s of a tactical fighting flashlight. -SF


In a previous post about lights I explained that lumens themselves weren’t the end-all-be-all of a flashlight or weapon-mounted light (WML). Well, they still aren’t, but maybe not for the reasons you’re thinking. I still want bright light; I just don’t want to be lied to or misled.

“More lumens = More Light = More Better”, right? Not quite. How the lumens are measured is important. There are three main ways this is done:

Emitter Lumens: This is the theoretical yield of a given light, using ideal voltage and thermal circumstances, and often tested with a math equation instead of real use. This is why you’ll see a $4 Chinese flashlight on Amazon (a worldwide purveyor of tactical tomfuckery) with a 5,000 lumen rating. The other reason is that they lie about it.

OTF Lumens: Standing for “Out The Front”. That is, the light that a given flashlight actually puts out. Maybe. Because everything in your flashlight is trying to steal the lumens from you. The reflector eats some. The lens eats some. Your batteries won’t always remain at peak voltage. Your flashlight gets hot.

Done properly, OTF lumens are measured with an integration sphere. It’s a device that fully encapsulates a lighting device, diffuses all light emitted, and gives you a reading. An OTF lumen rating is certainly better than inaccurate emitter lumen calculations, but could still be wrong regarding use. How? Let’s say you have a 1,000 lumen light but it only pumps out that intensity for 2 seconds before it drops down to 600. A company could still tell you that it’s a 1,000 lumen light, even though it’s much less regarding actual use.


ANSI Lumens: The American National Standards Institute, or ANSI, came up with a testing protocol for measuring lumens. ANSI lumens are also known as FL-1 lumens. It too involves an integration sphere. Testing first involves turning the light on for 30-120 seconds to ensure the LED is warmed up and the battery voltage sags a bit. However, since the testing protocols are known there are ways around it. Many flashlights have voltage regulation built in, and will force a light to step down in intensity if it’s been on for X amount of time. While one could argue this is for thermal regulation (preventing you from starting fires and shit) and to provide a longer and more consistent runtime, there are several companies that have this light step down occur immediately after the 2 minute period required for ANSI regulation testing.

To sum it up: Disregard emitter lumens. While OTF and ANSI/FL-1 lumens can be dubious, you’re best off going with a company that’s worth a shit in the first place. On the same token, just because a light steps down from constant use doesn’t mean it won’t be great for a weapon light. Think intermittent illumination rather than a Coast Guard search and rescue.

Read the Remainder at Breach Bang Clear