Will 150 emitter lumens still be brighter than 100 O.T.F. lumens?

I.E. will a Fenix Tank 20 be an upgrade from the KL5A? Just in terms of brightness per runtime, not build quality or finish etc (I'm already familiar with Fenix in that respect).

Or other 2xAA suggestions with latest L.E.D. technology.

The TK20 is suspected to be OTF, not emitter.

But even if it is emitter, yes, 150 emitter ~105-120 OTF > 100 OTF

More than likely your eyeballs won't be able to tell much difference between 150Lu and 100Lu...I wouldn't worry so much about the number advertised, as 90% of the manufacturers aren't exactly truthful to begin with.

What dano said.

A rule of thunb is that OTF lumens are light source lumens x0.66.
BUT ... that was determined with incan sources, so with LED YMWV. This also depends greatly on the components used, of course.

bernie

Kiessling said:

What dano said.

A rule of thunb is that OTF lumens are light source lumens x0.66.
BUT ... that was determined with incan sources, so with LED YMWV. This also depends greatly on the components used, of course.

bernie

Click to expand...

LED otf = emitter lumens *[.75, .80] with reflectors.

Do we have experimental data to back this up?
I'd be quite interested as we talk a lot about this and I always use the incan numbers.
bernie

Kiessling said:

Do we have experimental data to back this up?
I'd be quite interested as we talk a lot about this and I always use the incan numbers.
bernie

Click to expand...

Ask milkyspit.

He does not have an IS.

Then don't ask him.

Question is of no use.

ONLY if everything is the same, then there might be a difference to talk about.

As long as things like beam size or led tint are not absolutely identical, there is no anwer to the question

f.e. if the 150 lumen otf light has a 12 deg. main beam and the 100 otf the more common 8 deg, the 100 will seem brighter
(and someone not into lights for quite some time wont even notice the reason)


PS: imho all the newer lights are pretty much the same OUTPUT TO CURRENT WISE!!
There are fundamental differences in user interface, possibly materials and finishes, max current (very high output - low runtime), switches, parts to be enclosed to the shipment, ...
but overall the better offerings are identical.

Dont base Your decision solely on the highest number (if this is of interest, purchase at E-Bay, the offerings there are way brighter than the ones recommended here) ,
think of switch action,
User interface,
brightness settings,
remember last setting or not,
global "making" of the light (checkering, finish, materials)
battery choice
.
.
.
You like most

He already stated in the original post that he is interested in brightness per runtime and not build quality.

SnWnMe said:

He already stated in the original post that he is interested in brightness per runtime and not build quality.

Click to expand...

In that case, no difference between 150 emitter lumens vs. 100 out the front.

150 divided by 1/3 = 100

(Rough estimate).

He should just buy the one with longer runtime.

I already have the L5. I'm just wanting something that uses 2xAA instead of 2xCR123 that doesn't sacrifice performance. Any other quality 2xAA suggestions?

leon2245 said:

I already have the L5. I'm just wanting something that uses 2xAA instead of 2xCR123 that doesn't sacrifice performance. Any other quality 2xAA suggestions?

Click to expand...

eagletac p10a2 --- ~ 180 / 50 OTF lumens

youreacrab said:

eagletac p10a2 --- ~ 180 / 50 OTF lumens

Click to expand...

That's impressive. I'm assuming I'd need rechargeable batteries to get those levels, or any AA's going to be the same? Thanks for the suggestion.

NiteCore D20 and Fenix LD20 are both powerhouses.

Any of the current high quality 2xAA lights using a Cree XR-E will put out more light than the L5. The Lux V used in that old light isn't anywhere near as efficient as current LEDs. So forget the lumens rating and pick a light that has the features you want. You'll be happier that way. A good place to start is consider what type of beam you want, whether a flood like the L5 or something with more throw.

leon2245 said:

That's impressive. I'm assuming I'd need rechargeable batteries to get those levels, or any AA's going to be the same? Thanks for the suggestion.

Click to expand...

you need good rechargeables. Alkalines aren't going to deliver that kind of current that this light consumes to make that much light. I think I posted it drew over 1 amp from the eneloop batteries. Alkalines probably won't give you 20 minutes of useable runtime.

Kiessling said:

Do we have experimental data to back this up?
I'd be quite interested as we talk a lot about this and I always use the incan numbers.
bernie

Click to expand...

This can be understood analytically.

With incans, the following are the major sources of losses:

1. Inefficiency in the aluminum reflector
2. 8% Reflection from non-AR glass (some of which may reflect back out as spill)
3. Disappearance of light down the Hole at the base of reflector
4. Light absorption by crown bezel etc.

If the incan is replaced by an LED, all else equal, the following changes will happen

1. Less light captured by reflector as LED emits at most into 180 degrees
2. glass reflection effect should be similar
3. No "hole" for bulb lumens to disappear into
4. Light absorption by crown bezel etc. may be slightly more, as proportionately more lumens are going directly out-the-front as spill

The most dominant effect will be the absence of the hole, followed by the fact that less light is striking the reflector. This means that more lumens are making it out from LED light, but a greater fraction of those lumens are still rather than part of the spot.

Current TIR optics, despite the possiblity of being more efficient in theory, are similar efficiency compared to reflector based setups for the following reasons:

1. Insertion losses/reflection from the interior surface of the optic
2. Not all LED lumens at proper angle to reflect internally
3. refection loss from front interface (similar to 4% glass-air) -- unlike reflectors those lumens DO end up being completely lost

I believe however that if someone were to make a good TIR optic, actually index-matched to the LED directly, it would be possible to eliminate some of the interfaces, and also make the apparent die-image smaller allowing greater throw. Another possible improvement might come from anti-reflective coating the front surface of the optic where the light exits (NOT the whole optic, obviously). If these changes could be done I believe the ratio of torch lumens to bulb lumens could well exceed 90%.

Some manufacturers claim very high efficiency numbers for the optics, indeed.

The theory is fine, but the problem is the reality IMHO. I recall lenghly discussions about this problem with the incan light source, and a lot of very knowledgeable people needed a lot of time and thread to agree on something and come up with a factor as a general guideline.

I hope we'll have this for LED too in the near future.

Toaster ... the L5 is upgraded to an SSC P4 LED, so efficiency is the same. Absolute brightness is the same also, but runtime increased significantly.

bernie