Does reflector diameter affect actual or perceived brightness?

While walking tonight I started wondering how a reflector's diameter affects brightness :thinking:

For example, two flashlights with identical drivers/leds.
#1 - a P60 size bezel & standard OP reflector
#2 - a larger diameter bezel & similar design OP reflector

#1 throws a fairly wide beam, #2 throws a much wider beam
Both have equivalent throw/lux, the diameter of the beam is the only difference

Both are putting out the same lumens (compare w/o reflectors), would #1 appear brighter (actual or perceived) than #2 since the wider reflector is dispersing the beam across a larger area?

In other words, does the more confined beam area of #1 appear brighter when compared side-by-side to #2?

I lack two lights with the above characteristics to test, and wonder if anyone has observed whether this actually
occurs and if so why?

Thanks for the feedback

I think you need to take more than diameter into consideration. The depth of the reflector is also a factor.

If depth is kept the same and diameter is increased you will likely see wider flood but also possibly a tighter spot if the parabolic shape of the reflector has been changed as well.

With a deeper reflector you will get more throw and a less wide flood.

SCEMan said:

While walking tonight I started wondering how a reflector's diameter affects brightness :thinking:

For example, two flashlights with identical drivers/leds.
#1 - a P60 size bezel & standard OP reflector
#2 - a larger diameter bezel & similar design OP reflector

#1 throws a fairly wide beam, #2 throws a much wider beam
Both have equivalent throw/lux, the diameter of the beam is the only difference

Both are putting out the same lumens (compare w/o reflectors), would #1 appear brighter (actual or perceived) than #2 since the wider reflector is dispersing the beam across a larger area?

In other words, does the more confined beam area of #1 appear brighter when compared side-by-side to #2?

I lack two lights with the above characteristics to test, and wonder if anyone has observed whether this actually
occurs and if so why?

Thanks for the feedback

Click to expand...

What you describe would not exist though, the parameters are in conflict.

For example, if the lumen output is the same, but the beam is wider, the throw would be reduced, because the same lumens over a larger area would result in proportionally lower lux.

If the throw/lux are the same, but the beam is wider, the lumens would need to be increased to keep the same lux over the larger surface area covered by the wider beam.


So you CAN'T HAVE identical driver/LED do what you want them to in your example.





So, in reality, to get a wider beam with the same throw, you'd need a more powerful output.

You COULD get more throw with a TIGHTER beam and the same output though, as it IS possible at least to concentrate the same lumens into a smaller spot of light.....

...its just not possible to get the SAME throw, or more, with the same lumen output, AND a WIDER beam.

Good morning Mr TEEJ
I was just going to refer him to your excellent sticky on lux vs lumens

IIRC you discussed brightness and glare in there too, didn't you?

SCEMan said:

While walking tonight I started wondering how a reflector's diameter affects brightness :thinking:

For example, two flashlights with identical drivers/leds.
#1 - a P60 size bezel & standard OP reflector
#2 - a larger diameter bezel & similar design OP reflector

#1 throws a fairly wide beam, #2 throws a much wider beam
Both have equivalent throw/lux, the diameter of the beam is the only difference

Both are putting out the same lumens (compare w/o reflectors), would #1 appear brighter (actual or perceived) than #2 since the wider reflector is dispersing the beam across a larger area?

In other words, does the more confined beam area of #1 appear brighter when compared side-by-side to #2?

I lack two lights with the above characteristics to test, and wonder if anyone has observed whether this actually
occurs and if so why?

Thanks for the feedback

Click to expand...

Some things are little mixed up here...

-All else equal, the larger (wider and/or deeper) the head, the tighter the beam - so #2 should have a narrower beam.
-The tighter/narrower/more concentrated beam, by definition, will have greater throw and more lux (but both can have the same lumens though)

But yes, you are correct in that we see lux, and the higher glare/lux of #2's beam will appear brighter to our eyes, while the more floody/dispersed beam appears dimmer. Bounce both off the ceiling totally diffusing the light, and the ambient light will appear equal again.

EDIT: TEEJ beat me to the enter button

Good Morning Mr. Poppy.



I believe I did discus that.



And, yes, Mr, Reppans, as it was a made up example that could not exist in real life, the specs were not realistic, so a swap of tighter/wider etc, would be probable.

Thanks all for the replies...
As I was writing the scenario I realized it would likely be impossible (without a specifically engineered design) to have two reflectors differing only in diameter, produce identical throw/hotspot but with the larger one having a wider beam.

Appreciate the feedback validating this assumption.

I guess what prompted this thread was this thought; when reflected light is concentrated into a smaller beam, is it brighter than a wider beam with the same light source? I have seen beamshots of two lights with equivalent lux but with one having a wider beam/spill.

If one were to crop the wider beam to the same diameter/size as the other, would the narrower beam appear brighter since the light reflected in the cropped portion would be "lost"?

I realize this is hypothetical and probably useless but these are the kind of things that I think about on night walks...

You need to consider something like a Lenser LED light.

I find for walking a headlamp is best with a handheld torch for backup or for where long distance is required.

A lender such as the H14R.2 is a bit pricey and comes with a rechargeable 2 x 18650 2200mAh battery pack. It has a low of 60 Lumens (not dimmable), 350 Lumens (standard output) or 850 Lumens (up to 30 seconds or so).

I find the focussing lens very practical as it goes from wide flood with no spot to a focussed beam with over 300m reach.

This is why focussing lenses are made and they definitely have their uses.

I love my Eagletac MX25 L3 and my ThruNite TN12 but the Lenser H14 still gets used a lot and the longer the walk the more it gets used as I get tired of holding the light.

SCEMan said:

Thanks all for the replies...
As I was writing the scenario I realized it would likely be impossible (without a specifically engineered design) to have two reflectors differing only in diameter, produce identical throw/hotspot but with the larger one having a wider beam.

Appreciate the feedback validating this assumption.

I guess what prompted this thread was this thought; when reflected light is concentrated into a smaller beam, is it brighter than a wider beam with the same light source? I have seen beamshots of two lights with equivalent lux but with one having a wider beam/spill.

If one were to crop the wider beam to the same diameter/size as the other, would the narrower beam appear brighter since the light reflected in the cropped portion would be "lost"?

I realize this is hypothetical and probably useless but these are the kind of things that I think about on night walks...

Click to expand...

"Brightness" is perceived by how much overload of your eye's ability to compensate happens. After its overloaded, additional "brightness" is then based upon the SIZE of the glare. We tend not to perceive the dimmer, floody part of the beam as "bright", even if it took 10x the lumens to dimly light the larger area.


So, no, if you took a floody beam, and just cropped one part, it would be dimmer, as to GET the flood, the light was diluted TO spread it out and MAKE it floody.



So, again, if you have a given amount of lumens, and you concentrate them to make a small circle of light, you will have more lumens per square meter. Lumens/square meter = lux. Therefore, for a given lumen output, the smaller the area of light, the higher the lux.

If you have two beam shots of two lights with the same lux, but one has a wider beam, the one with the wider beam MUST have more lumens to have the same lux over the wider area.

Again, lumens per square meter = lux. Of you have more square meters, you need more lumens to get the SAME lux.

TEEJ said:

So, no, if you took a floody beam, and just cropped one part, it would be dimmer, as to GET the flood, the light was diluted TO spread it out and MAKE it floody. So, again, if you have a given amount of lumens, and you concentrate them to make a small circle of light, you will have more lumens per square meter.

Click to expand...

Thanks Teej. This is the explanation I was seeking