Reflector efficiency question

metalhed

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I have read numerous recent posts that discuss lumen losses in real world applications. And it seems that many feel that 35% is a good figure when it comes to losses due to a flashlght's reflector.

Recently I read an article discussing indoor light fixture efficiency and design. The article claimed that newer reflective surfaces in modern light fixtures can reflect up to 96% of the light hitting them. The article mentioned that this allows for many more placement options for interior lighting designers.

The reflective surfaces mentioned were all gloss white, not mirrored.

What I want to know is this:

Are we losing 35% of our lights raw output because of the quality of reflective surface? Should we be experimenting with non-mirrored refectors? Should we try some of these new white reflective surfaces? Are we stuck in old paradigms here?

Or does it have to do with the design of flashlight reflectors themselves (i.e., their shape.)

It sure seems to me that 35% lumen loss is unacceptable for a product that depends on batteries and other off-line power sources.


Can someone explain this all to me? What am I missing here? :shrug:
 

bwaites

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So far as I know, gloss white is not as effective as a mirror finish surface at reflecting light.

I'm confused by their statement that it reflects 96% of the light that strikes it, since that reflection level is possible with special coatings, but only with those coatings.

In torches, the reflectivity of the surface is only part of the problem, then you have problems with the lenses, losses out the back hole, and interior losses with the light that just bounces around in the reflector itself.

But 96% off a white surface? Wow!!!

Bill
 

metalhed

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I realize that the 35% light loss entails a lot more than just the effect of the reflector. But if flashlight reflectors approached the above referenced surfaces in reflective ability (say 90% even) then we are losing 25% of our bulbs output to these other factors. That seems really high to me.

Flashaholics have already learned that lens efficiencies can be improved dramatically with higher quality replacements (as much as 10%.) We know that LEDs lose efficiency and output as die temperatures increase, so we strive to provide superior heat-sinking for our lights. My Thor (with a H4 base bulb) fills the bulb-hole in the reflector with a reflective surface, so I know we can overcome that area of loss.

And yet...

I just can't help but wonder whether or not there are reflective and collimating options for flashlights that don't impose such an efficiency hit.


Or is this 35% figure an over-estimation? It seems to be a consensus figure around here, but are we wrong? :thinking:



I guess it just bugs the heck out of me that, when comparing lights, I/we agonize over the merits of output differences that seem trivial compared to that 35%. :rant:
 

bwaites

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I think I understand what is being said there:

Lets put a painted sheet of that material in a window of a room.

Then stand outside that window, with the reflective surface inside. Turn on an interior light, does any light get through? No.

Since it is not absorbing the light, what is the only other option? It is reflecting it, right?

BUT... It is not collimating that light, or directing it in any way, it is just bouncing it back, randomly at whatever angle it struck the sheet.

The problem is that if you then make the sheet flexible, and form it into a parabolic reflector, what happens? Some of that lights bounces around inside the reflector and never gets out, just like our reflectors.

Newbie can answer this much better than I can, but there are lots of new coatings that will eventually improve the performance of reflectors, but for now, with cost a big factor, we are stuck with what we have.

Bill
 

Kinnza

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Flashlights needs specular reflectors, white paint diffuse light, and it isnt a good idea if you want a directional beam.

But modern specular reflectors can achive near 90% reflectance. Less than 80% mean a bad reflector for actual state of art.

Actually, now its possible build flashlights wich only loss 10% at reflector and another 10-15% at the lens.
 

McGizmo

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At the speed of light, I doubt it takes a specific photon much time to either bounce out of a flashlights optic and window or get absorbed by same. Consider the size of a photon relative to the topography of the optic's and window's surface, at its scale.

If I recall my high school physics correctly (unlikely) a material has what is termed a critical angle. If the angle of incidence of a photon is less than this critical angle, the photon will reflect or bounce off the surface of this material with an angle or reflection equal to the angle of incidence based on a perpindicular to the surface point of contact.

Even a highly polished mirror surface has pits and deviations in its topography from the apparent contour as seen from a macro pont of reference. Individual photons are small enough that they may well encounter a point of contact in which their angle of incidence is greater than the materials critical angle and instead of bouncing off, they go in. If the material is a window and the photon is capable of penetrating or passing through, it will either transit if its angle of incidence is greater than the critical angle of the material when it reaches the boundary surface of the material or it will reflect off this boundary surface if the angle of incidence is less than the critical angle and continue on in a new path within the material. I assume at some point it either escapes or collides with an actual particle within the material and in this collision, the energy of light is converted to kenitic energy of heat? :thinking:

OK, I now admit that even if I recalled my high school physics, it was only a simple explaination of the physics involved and at some level, incapable of actually explaining what is really happening; limitations of man's modeling to represent reality.

These white and super reflective surfaces are for the most part lambertian in nature and even when they are formed at a macro level in a collimating surface, much of the light reflected will not follow the geometry dictated by the general form but rather the particular case of the surface at contact. At some level of significance a finely machined and surfaced optic is the pits or has the pits and some photons enconter these pits. :green:

For me, it helps to think of the world at a photon's level as not a world of solid objects but rather a world of objects that are a latice work with solid areas where contact or collision will occur as well as areas where a clear path through is posible. In the case of contact or collision, the photon may either glance or bounce of in a new path or splat into the mass leaving the mass in a greater state of energy or motion.

At a very simple level of consideration, we loose light everytime we attempt to make contact with it and alter its course. Whether an optic is based on reflection or refraction, it will not be perfect in nature and photons will be lost.

I have opted for relatively deep reflectors to be used with the Luxeons and when a collimated or concentrated beam is desired. Putting more reflective surface in the way of the stream of photons allows for a greater amount of redirection but at the cost of loss of photons. In simple and general terms, you pay for lux with lumen loss. It is this expense that confuses me when folks seem to expect that high lumen numbers equates to high lux numbers. In my way of thinking the two are typically somewhat inversely related due to loss in management or redirection.
 

LEDninja

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White electrical panels in the sun absorb less heat than stainless requiring less cooling. That means they reflect more.

White reflectors will be very floody. More lumens out the front but no throw.
 

metalhed

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Great answers here guys....and thanks McGizmo, that's the kind of analysis I was looking for.

I think I now understand some of the possible limitations and compromises that we make in designing collimation systems for lights.

An additional question tho'. As lighting efficiencies increase and as battery technology improves, it seems to me that portable lighting devices will be able to generate more and more lumen output. Is there a point where reflectors and optics will no longer be necessary for most general purpose lights?

For instance, we know that some spotlights (the Maxabeams, for instance) can throw light further than our visual acuity allows us to perceive (at least without aid.) This makes them impractical for general lighting use...they become impressive, specialized tools with superior throw and little else. But they are useless as general illumination tools. Their highly-focused output actually limits their usefulness.

Now when we are able to put a thousand lumens out the business end of a general purpose flashlight, will the average user need that light focused? Or is it possible that at some point the advantages of collimation (higher peak lux readings) are out-weighed by the lumen (and efficiency) losses?

With that 1000 lumens (or more), do I need a 'hotspot' any more for general use? If not at 1000 lumens, then at what level of output does a hotspot become unnecessary? A disadvantage even?

At these light levels, wouldn't a diffuse surface provide for more even lighting with (potentially) less lumen loss to reflector inefficiencies?

And if lights were designed with a 'one bounce' design in terms of photon management, couldn't we theoretically acheive the same 95% reflective efficiencies that state-of-the-art light fixtures display?


Can you tell that a 35% efficiency loss really frustrates me? :rant: It does!
 

McGizmo

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Metalhead,
I think the real issue is delivery of light on intended target and the target's size and distance from light source.

Most of us will opt for a 10% eficient light that delivers its output on target over a 90% efficient light that doesn't. Obviously the greater the efficiency of the light the better off we are in terms of not wasting energy. I guess I am trying to say that one needs to consider the efficiency of the ilumination application and not just the efficiency of the light source.

I made a Ti PD candle for my visit to Maui this year and it is the light I actually use the most. The highpower LED's are now capable of providing sufficient flux that they can be used in some applications sans any optics. I installed some optic free fixed lights in some works rooms at home before I came over here and they are actually significantly brighter than they need to be. This is the case with them being underdriven already!

I expect to see many LED based portable and fixed area lighting systems and regardless of their output, they will by definition be area lights if there are no optics used. Unless one actually desires to highlight or spotlight a specific section or field within the overall area, collimation is used because there is insufficient light for adequate and overall illumination. One is forced to compromise due to insufficient light output. Once you start to compromise and focus your available power, efficiency of luminious output is just one parameter in the compromise; flux another.
 

shiftd

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In a related topic (I think),


I have always wondered if smooth reflector and orange peel reflector have the same efficiency, assuming both were made using same process and material and whatnot. It is in my understanding that the more the photons have to bounce, the more light loss, and the energy got converted to heat to the reflector. That would mean that smooth reflector would have greater efficiency if compared with an orange peel one. Is my understanding correct? If so, how many percentage of the efficiency loss from using orange peel as opposed to smooth?
I understand that the intention of using orange peel is to smooth out the beam. Hows this approach compare to using a blurred lens, like LDF? Is one way better than the other?








One more thing, it seems that if the reflector coating is not thick enough, some of the photons can go through the coatings and into the material underneath it. This is clearly shown by IMS lines of plastic reflectors.

example pictures below:

dsc00315fa8.jpg



Yep, above was my custom flashlight with IMS SO20XA reflector in it. I used a tape as its window (lets not talk about this particular window losses
tongue.gif
)








Now, what happen if I turn off the light, and turn the flashlight on?

dsc00316lq5.jpg



The reflector is completely new and there is no hole at all in it. As the picture shows, you can actually see the light from the luxeon from the SIDE of the reflector. The light was currently running 350 mA to the lux. I would approximate at least 20% light loss there. The loss may not seem too big, but imagine if you have the multiple Luxeon III at fullpower, for example 10 luxeons U bin at 1 amps. Approximate lumens would be like 1000 lumens. If you loss 20%, you loss 200 lumens. That is like wasting 3 HDS U60 there, or wasted two of your U bins. I am sure they make the coating this thin to reduce cost, but this makes the reflector efficiency suffers so much, it is really not worth using it in high power lux application. It would be like an oxymoron that we tried to get every last bit of photon out of our poor luxeons only to have them running away through the spaces in between the coatings.

For aluminum reflectors, I dont think I would be able to see any light loss through the side. even if the coating might be as thin, aluminum is still kinda reflective (not like black plastic), so the loss might not be as much. But I cannot confirm that. (need help here)

so I guess if we dare to pay premium for our light engine, windows (gah, I rather call them lens), and converters, I dont see why we should be cheap in choosing our reflector.
 
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