Why does the Streamlight PP out throw a SF E2L?

I was checking through the flashlight reviews site and was wondering why the SL PP 4aa throws almost twice the distance of the SF E2L despite both having very similar output. I thought the SF optic was supposed to produce a very tight, long throwing beam?

jonman007 said:

I was checking through the flashlight reviews site and was wondering why the SL PP 4aa throws almost twice the distance of the SF E2L despite both having very similar output. I thought the SF optic was supposed to produce a very tight, long throwing beam?

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Well, the flashlightreviews.com site is not a gospel.

My Taskforce 3AAA is rated at higher total output than the ProPolymer 4AA Luxeon, but even with fresh alkaline batteries, the 4AA is noticeably brighter in the ceiling test.

The 4AA Lux was given 23 pts, Taskforce 3AAA was given 27 pts, both for total output.

jonman007 said:

I was checking through the flashlight reviews site and was wondering why the SL PP 4aa throws almost twice the distance of the SF E2L despite both having very similar output. I thought the SF optic was supposed to produce a very tight, long throwing beam?

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You can't look at the numbers that way. "Throw" is a combination of quanity of light and how tightly it's focused. Lux is lumens/meter^2. The "Throw" value is taken at the center of the beam. The "Overall Output" value is taken by shining the light into a lightbox that bounces around all the light inside it, with the light meter taking a general reading of the light inside the box. Another way to see overall output despite different beam patterens is called the "ceiling bounce" test, where you point the flashlights at the ceiling and look at the walls or at the floor and see which light lights up the room more.

The point is, the values can't necessarily be compared against each other in the manner you're thinking. More than the numbers have to be considered (chiefly, the beam profile).

Also to be considered is the Inverse Square Law. Basically put, if you double the distance, you need 4 times the light to illuminate it equally. Similarily, if you double the light in the same beam profile, it only throws 25% farther.

As for which outthrows the other, the E2L or the PP, I can't say; I don't own either.

Planterz said:

You can't look at the numbers that way. "Throw" is a combination of quanity of light and how tightly it's focused. Lux is lumens/meter^2. The "Throw" value is taken at the center of the beam. The "Overall Output" value is taken by shining the light into a lightbox that bounces around all the light inside it

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Hence the perceived brightness from the ceiling bounce.

with the light meter taking a general reading of the light inside the box. Another way to see overall output despite different beam patterens is called the "ceiling bounce" test, where you point the flashlights at the ceiling and look at the walls or at the floor and see which light lights up the room more.

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You're preaching to the choir. You must not have seen the words "ceiling test" in my post

To clarify myself, comparing the perceived brightness of the room with the flashlight being tested shining at the ceiling, the SL 4AA produces a higher level of perceivably brighter atmosphere than the TaskForce 3AAA despite the "overall output" figures on flashlightreviews.com saying the other way around.

Clear enough?

I was replying to jonman007's post. You squeezed yours in before I was finished. Sorry for the confusion. I'll edit mine to quote his to clear this up.

Planterz said:

Also to be considered is the Inverse Square Law. Basically put, if you double the distance, you need 4 times the light to illuminate it equally. Similarily, if you double the light in the same beam profile, it only throws 25% farther.

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i believe it is about 41% farther.

Er, yeah. For some reason I was thinking the square root of 2 was .25

Welcome to CPF by the way.

ok then, i guess my question becomes: does the SL PP out throw the SF E2L? and if so, why?

As far as I am concerned, the two lights have similar overall output. SF rates the E2L at 30 lumens and Streamlight rates the PP at 40. Considering the usually conservative figures quoted by Surefire, it seems fairly obvious that the two lights have similar total output. This is supported by the figures on flashlightreviews.com.

Therefore, as the two lights output very similar amounts of light, the only factor affecting throw would be how tightly the beams are focussed. I have been led to believe that the TIR optic on the KL1 produces a very, very tight beam without much sidespill. Hence, I would assume the E2L would throw further. Am I wrong?

The tightness of a focused beam is physically limited by the diameter of the focusing optics and the size of the emitter. While the emitters used by the E2L and SLPP are the same size, the SLPP reflector is larger than the E2L optic. The larger objective diameter means the SLPP can out throw the E2L even though both lights have approximately the same overall output.