What exactly is "Usable Light"?

[KSDbass]

I'm looking into getting an LED surefire, either a conversion for my E2E, an L4, or an L2, but I'm curious as to what "Usable Light" is. For instance, I can get 1 hour of 100 lumens, followed by up to 2 hours of Usable Light with the E2E conversion. However the L4 does 1 hour of 100 lumens followed by 3 hours of Usable Light.

My question is, is usable light a consistent term, or is different for each light? And if it's consistent, how many lumens is it?

[Lockback]

"Usable light" is an intentionally vague term; it does not have a specific equivalent lumen amount. It varies from light to light.

As I understand it, the term "usable light" is used to differentiate light that is, well, usable - not the original lumen rating, but still enough to light a path, read, etc., as opposed to the "moon mode" glow that many LEDs exhibit for a long time after batteries reach a certain discharge point. I think most people would classify a weak glow as "unusable light," so "usable light" would be the period between the full rating, and a glow.

[vampyrewolf]

For me, it's enough light to read by.

"usable light" on my 6P drops the 120lumen from the P61 head down to around the 60lumen the (original) P60 head puts out. All told there is about 15-20min of that before the batts "die" in the SF... They're still good for 15-20hrs in my X5 at that point though, so I haven't bought new batts for a while

Just about a perfect combo there... get a SF for the lightsabre brightness, and an X5 for the other 60-70% of the batt life.

I've got cheap lights that put out near that 60lumen for a couple hours, running on 3xAAA... cheap as in almost disposable at $4 a pop.

[Civilian]

seems to me that it would mean light that is noticably lower than full power but still useable for non "tacticile" purposes.

[J Smith]

I would think that when the batteries get low enough not to be able to power the light at full power it starts fading off.I have a L1 that has a 1 lum on low beam and it is good enough to use in a car at night so I would say that the usable light would be anything over 1 lum.

[Monocrom]

An L4 is basically an E2e with the K4 head installed. If you can live without a Xenon-bulbed E2e, just get the K4 head for it. If you want both, buy an L4. I love my L4.

An L2 is longer than an L4. I find it to be a bit awkward to use and I don't need the lower setting. (I carry a Photon II on my key-ring when I need less output). But if the length doesn't bother you, it's also a very good choice.

[Darkfin]

I think "usable light" is light above 50% of full battery lumens. At least that is how Flashlightreviews.com seems to look at it.

I use a 6p with a CREE drop in assy. It is 120 lumens, and after about 45 min of intermittent use on these surefire 123's, I notice no discernible drop in illumination. CREE is FAR better to incandescent!

[Jimd]

For me, it's enough light to read by.

I agree with VW.

I also use my 123 batteries in the same manner - when they won't power my SureFire incandescent light, I throw them into my LED lights, where I can use them for a loooong time.

Usable light isn't going to blind anyone, that's for sure. But you can do menial tasks, maybe like change a flat tire, or read, or see your doorknob to insert the key. Stuff like that.