OTF Lumens - reflectors and lenses

I know a lot of you have done extensive reviews for lights using many different instruments to measure OTF lumens for lights. In your experience or comparisons, what percentage of light do you lose by not having a coated lens and standard plastic reflector?

I guess the question is really, is the difference really that significant when you have a coated lens and a polished metal reflector?

When I was doing OTF lumen testing the reflector material made little if any difference.

The normal glass vs. AR Coated made 8~10% difference.

Plastic vs. AR coated up to 15% or more.

Another fun fact. Those huge Surefire tactical tailcaps that sell for up well over $100 bucks for 6P’s. Those would take away over 20% of the OTF lumens. I found the tailcaps to be the 2nd main offender after the glass.

Now, the main killer of OTF lumens came from using Aspherics. Those when the die is perfectly focused can rob you of 40~50% of the OTF lumens. Fun as heck but thief’s those Aspherics are.


So those zoomies are lumen thieves, huh? That’s good to know. I guess if the light is trying to squeeze through a thick piece of curved plastic, it makes sense that some of it is blocked.

Also, how does a tailcap affect lumens? I’m not sure I follow.

Tailcap or switches have resistance stock. Some bad some really bad. Oveready.com address that by selling brass inserts for Twistie switches. Dioxit spray also helps

Spring bypasses pretty much eliminate the tail cap resistance.

As for why aspheric’s lenses have such a high lumen loss when zoomed it- it’s not that the lens is blocking the light, especially not a good high quality aspheric lens, it’s that the farther away the lens is from the emitter (i.e. zoomed in) the less light reaches it in the first place. You’ve got the inverse square law working against you as well as the side scatter of light causing more and more of it to miss the lens all together.

Personally I have no issues with plastic reflectors, I think people get way to hung up over these. Ok they could melt on a high powered incan setup, but leds don’t put the heat out the front the same. And usually the reflector has little or no affect on heatsinking.

While I agree that those principles have a hand in affecting the light, I’m going to go out on a limb and say that most zoomies that we encounter use cheap plastic for the lenses.

The light ends-up being absorbed by the interior wall of the head. It makes me wonder what would happen if the interior of the heads of a zoomie was plated similarly to a reflector. Doubtless it would be flood, but it would help get more light out the front than simply wasting it.

It would be a nice experiment for someone here to try. :smiley: A quick wrap of some aluminum foil could see if there’s a difference at all. Haha.

Or a Wavien collar to recycle the light and send it back out toward the lens?

I have 4 aspheric lens right now for my Maglite builds. I like mine right in middle of flood and throw. A huge big circle for daily use. Anyhow, putting the stock Maglite reflector in addition to the aspheric I can visually see the intensity increase but the beam gets more fugly. So, yes a reflector with aspheric combo in my setups definitely gives more noticeable light.

What would happen is a beam full of ring’s, there’s a reason JAX Z1’s and other higher quality zoomies come with everything inside the head blacked out.

Most cheap zoomies use PMMA, an optical plastic with very good light transmittance. Again the MAIN factor in the lumen loss when zoomed in is the inverse square law. The farther the lens is from the source the less light it captures and projects. Yes a low quality lens makes it worse, yes scatter from light going out to the side cost’s OTF lumens but the main thing is the distance from the LED that the lens sits.
If you have 2 identical size lenses, made from the same glass / PMMA, the same diameter using the same LED but the lenses having different BFL’s (Back Focal Lengths- the distance the LED needs to be to be perfectly focused, cause “focal length” only matters with point sources like lasers) the lens with the shorter BFL will loose less lumens when fully zoomed simply because it doesnt have to be as far from the emitter so not as much light is lost due to the ISL

Maybe you can help me understand this better, but from what I’m reading, the inverse square law in regards to lighting is a formula to show the intensity of light on an object as it gets farther away. But in the case of an aspheric lens in a zoomie, it would seem the only reason why you would lose lumens is side scatter because of the way light is dispersed, and then because of the ISL. As it the lens gets farther away, and the light is dispersed, the light that would normally hit a reflector is absorbed by the wall of the flashlight. But I can’t imagine that ISL is applicable for a distance of mere inches in regards to a zoomie at flood vs. zoom.

The inverse square law works at all distances.
A lens at 1” gets one quarter of light it gets at 1/2”.

Ok. So let me get this straight… light scatters BECAUSE of the ISL… so light that would normally hit the lens is now dispersed elsewhere because of the slightly greater distance. And that dispersed light is now absorbed by the black wall of the flashlight. So if you ask me, I’d say ISL and side scatter are tied for being lumen thieves. :bigsmile: I don’t know. I’m just some normal Joe trying to understand of all this.