The Real Reason for Throw - an in depth examination

[bbb74]

Here's the same calculations but for the xr-e.

The only change in this table vs the xp-g one is that the xr-e definitely has a very different light intensity at various angles off centre from the xp-g. Its putting out hardly any light at 60 degrees off centre, while the xp-g is still at 40% of peak intensity. Obviously you'd need quite a different reflector shape/size for an xr-e vs an xp-g Well designed reflectors that suit the emitter would probably negate much of the differences in the varying output at angles off centre. I can't really comment out how this makes the xr-e as a better/worse potential thrower vs an xp-g but I think the emitter brightness intensity as described by saablaster is much more important.

Please note I don't take into account how much light is lost when it hits the reflector vs going straight out the front without hitting the reflector. I don't know how much is actually lost by the reflector, and I imaging it varies depending on the angle the light hits the reflector.

 

[TooManyGizmos]

~

I deleted my off-topic and ignorant post .

Sorry for the distraction .

~

 

[easilyled]

Thanks for the research and the interesting distribution figures, bbb74.

As you say, good reflector design appropriate to the type of beam angle and distribution probably cancels out the beam distribution and angle being a factor in throw.

However simply because the reflector actually needs to be a different shape for an XRE, ie narrower and deeper to catch its beam effectively,
the diameter of a reflector for an XRE has to be less to achieve the same throw than for an XPG, assuming the same surface brightness.


Therefore deliberately selecting an XRE helps to keep the width of the head smaller than it would have to be in order to achieve the same throw with a different emitter with wider beam angle and the same surface brightness.

This can be advantageous for pocket throwers.

 

[bbb74]

However simply because the reflector actually needs to be a different shape for an XRE, ie narrower and deeper to catch its beam effectively, the diameter of a reflector for an XRE has to be less to achieve the same throw than for an XPG, assuming the same surface brightness.

Therefore deliberately selecting an XRE helps to keep the width of the head smaller than it would have to be in order to achieve the same throw with a different emitter with wider beam angle and the same surface brightness.

This can be advantageous for pocket throwers.

Actually I totally agree

And at the end of the day the lesson is what saablaster said - that increasing surface brightness is the first step out of several to get better throw. The beam angle isn't that much of a factor if the designer does their job. As you say, smaller beam angles may let you shrink the head vs a wide beam angle.

 

[MikeAusC]

Lens Capture vs Angle

So if I'm using a lens to capture the light, it's now easy to see how much impact there is on gathering the light, as I change the lens size or LED type -

LED ---- 40 deg ---- 50 deg

XP-G ----- 44% ------ 62%

XR-E ----- 73% ------ 94%


So if I increase the lens size to capture +/- 50 degrees of the beam in front of the LED, instead 40 and you change from an XP-G to an XR-E, you will MORE THAN DOUBLE the percentage of light being captured by the lens i.e. 44% to 94%.

 

[Nitro]

SO, did we ever figure out what Throw is, and the reason for it? :laughing:

 

[Dude Dudeson]

SO, did we ever figure out what Throw is, and the reason for it? :laughing:

"I may not be able to define throw, but I know it when I see it".

 

[easilyled]

SO, did we ever figure out what Throw is, and the reason for it? :laughing:

Sure, Throw is a relative measure of how far out the darkness can be busted by light. The reason is bragging rights.

 

[Mr. Tone]

Sure, Throw is a relative measure of how far out the darkness can be busted by light. The reason is bragging rights.

I like this definition. :devil:

 

[Dr.Jones]

There are some threads on throw, partially about lens based throwers, though:

Optics theory
Calculating throw

Throw can be defined as the distance in which the flashlight's illuminance on a target falls below a certain level, e.g. 1 lux. However that value (1 lux) is just a commonly used value, I have seen Maglite using 0.25 lux instead. 1 lux should be sufficient to see things quite well, but that depends on what you see: A white wall with dark windows needs less illuminance to be clearly seen than a dark tree in a dark forest.

<EDIT> That 0.25 lux for throw calculation actually is a new standard called "ANSI/NEMA FL1". 0.25lux is quite low for practical purposes, unless you live in a snow-covered area. I guess the manufacturers had some influence... </EDIT>

That distance can be calculated from the luminous intensity (measured in candela, cd) of the flashlight's center spot (often called spot brightness), using the inverse square law:

d = sqrt(I/E0)

where d is the throw distance, I is the flashlight's luminous intensity, and E0 is the minimum illuminance as specified above (typically 1 lux).
You need a fourfold intensity to get twice the throw.

The spot intensity is often (and somewhat incorrectly) referred to as "lux @ 1m (calculated)", because a light source with a luminous intensity of, say, I=3000cd will yield an illuminance of E=3000lux in d=1m distance, according to the above formula rearranged:
E = I / d^2

A flashlight's intensity (and thus throw) depends on 3-4 factors:
a) the emitter's luminance (surface brightness),
b) the effective apparent area of the lens or reflector,
c) losses (reflection, absorption, scattering) and
d) losses due to lens/reflector errors (imperfect shape).

Most interesting, the focal length of a lens and thus the deepness of a reflector does not have a (direct) influence... The reflector's deepness may have an indirect influence though: the inner part of a parabolic reflector is not used with a LED since no light falls onto it, so that area has to be subtracted from the apparent reflector area (that's why I wrote 'effective' apparent area).

 

[Mynock]

Hi saabluster,

I wish to thank you for taking the time to share your knowledge. For someone like me new to the flashlight world it has been invaluable, not just for understanding 'throw' but also for the basic principals of why certain LEDs are better for different tasks. This is exactly why I came to cpf

 

[Mr. Tone]

saabluster, this thread needs to be revived with more info and discussion. I would love to hear about the strengths and weaknesses of different illumination tech and their potential for throw. I mean incandescent, LED, HID, short-arc, etc. I know you are crazy busy and maybe there needs to be a separate thread for just the tech, but I figured your thread is the right place or at least a good starting point for that conversation. It would be fun to know, for example, how far an overdriven de-domed LED such as XP-G2 could perform in a large high quality reflector like in Ra's Maxablaster, or even an aspheric that large with and without a Wavien collar. I know that getlit's Nightsword project is producing a crazy amount of lumens and candlepower, but he has experimented with various lamps if I remember correctly so the current figures I don't know. The initial project was putting out around 75,000 lumens from a 3.5 mm arc but I think he found something better to use since that first rendition.