Create a focused beam angle of LED light using reflection

[jason3w]

Summary: Will an external surface reflect light into a more focused beam without using a traditional lens?

Hey guys.
Just trying to focus the light coming from a 1watt LED light source. It's native beam angle is 130 degrees. I'm hoping to focus it to around 30 degrees.
We are creating an enclosure around the LED with polycarbonate. So we can have a smooth reflective surface around the LED.
If creating this surface on an angle as shown below, is it likely to redirect most of the light?
Image http://prntscr.com/nyowlu

Many thanks in advance.
Jason

 

[davenn]

Summary: Will an external surface reflect light into a more focused beam without using a traditional lens?

Hey guys.
Just trying to focus the light coming from a 1watt LED light source. It's native beam angle is 130 degrees. I'm hoping to focus it to around 30 degrees.

HI you Jason
welcome to PF.
You have tagged your thread as an A for post graduate level. Assuming then that you are post graduate level, you must be well used to doing research when you did your degree.
What work have you done so far to get some answers to your query ?

Here at PF we love to help people that help themselves and run into problems that we can
guide them through


Dave

 

[BvU]

Don't think this is PHD work...

But indeed: what did you google up so far ? Why do you think car lights have parabolic mirrors ?

 

[berkeman]

You have tagged your thread as an A for post graduate level.

Thread prefix changed to I (undergraduate level).

 

[sophiecentaur]

A parabolic mirror can give as narrow a beam as you want (subject to diffraction and aberrations) from a source (bulb etc.) as long as ‘all’ the light from the source is intercepted by the reflector. Your 130 degree bulb is a bit wide in practice perhaps for that criterion.
Also you do not mention what area of spot is needed and how far away the focus will be. What efficiency ( light loss and beam spread etc.) can you tolerate? It could be dead simple or nearly impossible, depending!

 

[BvU]

Google is your friend:
This link is not meant as a commercial ( they are out of stock anyway ) but as an example. There's even a measured drawing ...

 

[jason3w]

Thanks guys for all the info. Yes, I did make a mistake with the listing it seems. I actually didn't finish high school. Though I did get straight A's in Physics up until the year I left. Still, that was some 25 years ago.

Thanks sophiecentaur. That's helpful. This light will be inserted into a polycarbonate tube and I'm aiming to fill as much of the tube with light as possible. The tube is frosted. Directing the beam to 15degree beam angle is very effective as I've tried this with the 15degree 5mm LEDs but want to replace with the 1w type which doesn't come in such a narrow beam angle.

Your mention of the parabolic reflector has helped a lot too as that is clearly the lens I'm trying to create. I've now found how to make a parabola that will work in this case. Only they are mostly talking about the focal point which i gather in my case would be the light source itself.

I'm still unable to find info on whether it will work with a clear, yet reflective, surface compared to a mirror.

I did use a solid polycarbonate lens which sits over the len and the light enters the polycarbonate and on exiting it's shaped to a more focused beam.

I did google a bit on reflection and refraction to try figure this out before posting too. From what I found the light will bend on entering or exiting a new substance. Though in my case i'd like it to not really enter the new substance as much as reflect off it and focus the light forward.

Summary:
Will the clear parabolic reflector still function to a degree? If so, to what degree of efficiency would one expect to achieve in this?

If this "external" reflector wouldn't work i guess I'm better off going with a solid lens.

Thanks again!

 

[CWatters]

I'm still unable to find info on whether it will work with a clear, yet reflective, surface compared to a mirror.

The percentage of light reflected Vs refracted will depend on the angle of incidence and the refractive index of the material. At shallow angles most light is reflected, at steep angles most is refracted. For glass the angle at which 50% is reflected/refracted is typically quite shallow, perhaps 75-80 degrees to the vertical (normal).

 

[sophiecentaur]

@jason3w you mentioned “filling a tube with light. To get really good, uniform illumination of the end of a tube, you may find a totally different system is easier and could be more what you need. A cuboidal tube with four sides made of mirrors and a frosted end with the light behind it will produce a great, even illumination at the other end. I used such a ‘light tunnel’ for illuminating slides with great success. (Just a suggestion).

 

[davenn]

Your mention of the parabolic reflector has helped a lot too as that is clearly the lens I'm trying to create.

a parabolic reflector is a mirror curved as a parabola it isn't a lens

I've now found how to make a parabola that will work in this case. Only they are mostly talking about the focal point which i gather in my case would be the light source itself.

yes, because the light source has to be at the focus. The parabola then reflects the light out as a beam

I'm still unable to find info on whether it will work with a clear, yet reflective, surface compared to a mirror.

there isn't one, other than by doing what CWatters said back in post #8, the angle has to be very low.
Shining light directly onto a non-mirrored surface, the light will go through the material.

Though in my case i'd like it to not really enter the new substance as much as reflect off it and focus the light forward.

see previous comments

Will the clear parabolic reflector still function to a degree? If so, to what degree of efficiency would one expect to achieve in this?

not really ... most of the light will pass straight through ... efficiency = very low maybe a few %

If this "external" reflector wouldn't work i guess I'm better off going with a solid lens.

Well that is the normal way, it's done with lasers all the time, think of every single laser pointer out there. The process is called collimation

there's really no need to try and reinvent the wheel

 

[sophiecentaur]

@jason3w it would help a lot if you were to describe exactly what you are trying to achieve. You may think you have described what you want but I done't think it's clear enough for PF to give you the best solution. (PF discussions can chase in many different directions and easily leave an OP out in the middle of nowhere) If you want an area / target that's uniformly illuminated from one direction then a lens / reflector system could be what's needed. In fact a lens would be best if the optics needs to be short / small. Using a reflector could introduce a shadow due to the source getting in the way - a wide reflector would be needed to eliminate any shadow. But you need to say how uniform you need the illumination to be. That would probably mean you need to describe the actual application.
If the illumination needs to cover a big range of angles then my suggested light tunnel would do the job, achieving the same result as a very wide paraboloid reflector.
So some details of what you actually want would be helpful.