LED optics, reflectors and front perspex covers

chris_m

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I'm currently building up some LED lights, and have a couple of questions:

I'm using LED specific optics (clear plastic), however I note people using metallized reflectors here. Is there some efficiency advantage to the reflectors, or are they simply what fits the flashlights you have?

I'm thinking of putting a front perpex flat sheet on my light - at least partially to protect my optics, as it's cheaper and easier to replace this if it gets scratched. Will I suffer from a significant efficiency loss due to the two additional air/perspex interfaces?
 

Ganp

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Hi Chris,

Unless the optic is silvered on the back I think it unlikely that it will ever be as bright as a good reflector.
I'm with you on putting a protective window over the front of the optic though. IMHO the light transmission quality of the material will have a bigger influence on light output than the number of air/material surfaces.

It would be nice to see some pictures of your builds when you have done them. :popcorn:

Colin.
 

Ra

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Hi Chris,

To make the confusion complete, I'm going to tell you the oposite: The plastic optics you mention are the best aviable !! They don't need a reflective coating. They use the 100% reflection-law of light !

The generally used metal-reflectors have an efficiency of about 80-86%. The plastic optics have an efficiency of over 95%. They are desighned to work well with the dome-shaped luxeons and cree's. And reflect almost all bulblumens into torchlumens!

The disadvantage of the plastic optics is that they need to be very clean and undamaged to reach their efficiency.

A huge advantage: You are not blinded sideways by the led because all of the light is optically grabbed and put into the main beam: Even the lightloss that would occur as a result of the center hole of a conventional reflector is focused by a central lens ! (clearly noticable on the pictures)

Edit: With clear mastic silicone I glued a glass window (1mm thick) on top of the optic to keep it undamaged: Also preventing lightloss at air-surface situations..


reflledfw0.jpg


and..

dsc01883biy5.jpg



Regards,

Ra.
 
Last edited:

Ra

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Thanks mosport,

I didn't know about that thread !! And didn't know that the difference would be that big !! I'm an optical engineer so know from theory that metalizing those optics would be a very bad idea !!

Regards,


Ra.
 

mosport

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Hi Chris, here's a more recent thread on reflector efficiency with some great information. Losses aside, choosing between reflector or optic focussing will also be influenced by their individual beam characteristics, your requirements and personal preferences. Plus as you mentioned, if it'll even fit.

I protected a recent Fraen mod with an anti-reflection coated UCL lens (~98% light transmission), with a 1mm air gap between the optic and lens. Not sure about the losses caused by the additional interface, but should be less than from a scratched up cloudly optic left unprotected :)

img1070wg6.jpg



Thanks for sharing your professional expertise with us too Ra, I was researching old threads for my mod above and your name appeared several times in the hits.
 

Ganp

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Chris,

If you have not already done so, you can contact Fraen, Carclo, and probably others, who are often very obliging in supplying samples of their optics to experiment with.


mosport
Losses aside, choosing between reflector or optic focussing will also be influenced by their individual beam characteristics, your requirements and personal preferences. Plus as you mentioned, if it'll even fit.
Second that!!!


Ra
The plastic optics have an efficiency of over 95%

Hi Ra - I bow to your optics expertise.:)
I use Fraen and Carclo optics, and they claim only 85% efficiency WSBA.
For flashlight purposes is not the efficiency within the specified beam angle of more relevance than the total light output?


Colin.
 

chesterqw

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fraen and carclo claim to have 85% only because, they calculate it according to what the optic rated beam angle is e.g. 6 degree.

the only take the light in that 6 degree and don't care about the light outside of that 6 degree.(the spills)
 

yellow

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each media transition costs light.
Optic: 1 time in, reflection, 1 time out
Reflector: 1 time reflection.
so I would say a good reflector will be equal or better than any optic.
then there is the front cover (glass). Most ppl use such even with an optic, so another unnecessary loss, because the optic already is sealed to the front (I use a front glass also, no need to critisize) :)

Finally the most obvious difference: focusing
MOST of the optics used around here tend to be around 10 degrees or more, reflectors usually are tighter and thus better throwers, while still offering a good spill light.

Dont ask me why, I started with Fraen LP and NX05 and such, but after trying my 1st IMS, I was lost. The tighter beam is much better for outside lighting and inside rooms not this worse NOT to use a reflector (in comparison to an optic)
AND
when using an optic, all the space around the emitter (behind the optic) is lighted up. This means to me that there is light wasted and not getting out front.
I hate that ;)
 

Mad_mat222

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Excuse my ignorance, but what is the difference between a reflector and an optic? Is the optic the unit as a whole including emitter and reflector?

ceers
 
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