Reflector loss (output)

easilyled

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Jun 25, 2004
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Is it true that different sizes/shapes of reflector can significantly
influence total light output?

I have noticed in 2 lights that I have using the McR27L reflector that
the total output isn't quite as much as expected for the drive
levels of these lights, compared to lights with the same leds
and drive levels but using smaller and shallower reflectors.

Both these lights also have sapphire glass, whereas the others have
UCL lenses, but my understanding is that the difference in output from
using these 2 different windows would be almost impossible to detect,
whereas in fact its quite noticeable.

I don't know much about optics but perhaps the length and overall surface
area of the 27L results in less overall light being reflected out the window
and more light being aborbed beforehand?
 

THE_dAY

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long ago when i had just gotten my fireflyII, i was trying out the ims17mm plastic reflector and the Jil 17mm aluminum reflector in it.
the ims 17mm was definitely giving a brighter overall beam than the Jil reflector.
also since the Jil reflector was slightly yellower, it gave a slightly yellower beam.

both reflectors were brand new and very clean but i could see my reflection in the ims17mm a little clearer, basically it was more reflective.

as for size, i would guess that a smaller reflector would have less light loss since it has less surface area but i have no means of testing this.
 

IMSabbel

Enlightened
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Dec 4, 2004
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Of course the shape and or type of a reflector can make a difference in output, or would there be any reason to spend time developing them? :)

For example, you have to keep in mind that the reflectivity and transmission numbers for windows and mirrors are usually normal incidence, unpolarized.

Also you have to consider that even the most perfect, non diamagnetic mirrors (which only work well for lasers) will only reflect about 96-97% of the light. And thats a perfect finish in vaccuum. If your mirrors and window are a bit dusty/dirty, ect, the total losses (reflection, loss of light not captured by the reflector, loss at air/saphire, loss at saphire/air could add up to 20% easily.

But still thats a little slim to be obviously visible to the naked eye.
You sure that your can gauge the brightness well enough to have a good feeling of exected output for a certain drive level?
Did you check how hard the lights are actually driven?
 

easilyled

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IMSabbel, consider 2 lights with the same SSC-P4-U-bin Seoul
led, both driven at 525ma with very reliable drivers.

One is using a McR20-S reflector, the other a McR27L Seoul reflector.

The point of these different reflectors is to create a different beam
pattern. However I don't think a variation in actual total output
is intended.

The light with the McR27L reflector produces noticeably (maybe 10%) less
overall light in a ceiling bounce test, no other equipment is necessary to determine this.

I have also noticed the same phenomenon between 2 lights driven at
917ma, one with McR27 and the other with McR27L. Again both
have Seoul leds and again the McR27L is noticeably less bright.

I don't know if you're familiar with these reflectors but the McR27L is
much longer and has much more surface area than both the McR20-S
and McR27 reflectors.

So I am postulating that a significant amount of light is lost in the McR27L
and therefore less light is transmitted due to the larger depth and
surface area.

This is not a complaint because the McR27L produces a fantastic beam
and performs the function that Don (McGizmo) designed it to do
superbly.

I am just asking whether anyone who is knowledgeable enough to comment
thinks that this is the case, or whether its just a coincidence that the
2 lights that I have with McR27L reflectors produce less total output
than their counterparts with shallower/smaller reflectors.

It stands to reason that the larger the area that the light rays have
to "bounce" on before they are finally reflected out the window, the
more some of them will be absorbed because there is no such thing
as a 100% perfect reflective surface. Also these reflectors have a light
stippling which will also no doubt absorb more light than a completely
smooth surface.
 

cave dave

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Don't forget the Lux Lottery. Two SSC emitters from the same bin code, can be up to 20% difference in luminous efficiency.
 

easilyled

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Jun 25, 2004
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Location
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cave_dave, yes you're right that the lux lottery is a possibility.
But I have noticed a really high consistency between all my lights
with Seoul leds using the same reflectors. I have 2 PD-S's which
are virtually identical in output.

Calina, yes you're probably right that I should ask McGizmo himself
(and he might decide to chime in if he sees this.)

I deliberately didn't put it in his forum though because ....

a) I don't want it to appear as a complaint or criticism
because it most certainly isn't

b) I thought it might be a topic of general interest anyway since
the same principle could apply to other reflectors with different
sizes, designs and shapes and I was hoping that there may be
one or two of us around here that know enough about optical
physics to confirm or dismiss this.
 
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