Re: how to get a crisp circle of light

On Mar 28, 3:30 pm, H. Wabnig <.... .-- .- -... -. .. --. @ .-
--- -. DOT .- -> wrote:
On 28 Mar 2007 00:01:52 -0700, "rahul" <rahul...@xxxxxxxxx> wrote:

Hi,

Pardon my non-optics language - I am a product designer by profession
and need your help/guidance. Currently designing a special purpose
Flashlight based on 1W Lumiled LED (beam angle-125). My concern is to
get a very uniform spot of bright light of about 50 mm at a distance
of 420 mm. Beyond the edge of circle there should not be any light
ideally.

Can some one guide me how to go about it ? I have been experimenting
with off-the-shelf optics available for the LEDs but with no luck.

To > >Thanks
Rahul Kaushik

You did not give enough information.
How good must the uniformity be on the target?
With my eyes I only perceive a brightness difference of about 20%,
less than that is not easy to recognize.
A uniformity of about 1 % is very hard to achieve and
only possible with considerable brightness or intensity loss.

Design it for 150 mm diameter, then put a 50 mm stop directly
on the 420 mm image plane.
Use an array of LED's and project it on the target.
Or think of using a collimator and fly eye lens combined with
a projection optics, or otherwise use a cylindrical or prismatic
glass rod "light pipe" for obtaining better illumination uniformity,
or use an elliptical reflector. Buy an old slides projector on the
flea market and use it's collimator optics.

A list of optical design software:http://www.optenso.de/links/links.html

An example from above list:http://www.opticalres.com/lt/ltprodds_f.html

w.

Thanks, Wabnig for the direction.

To answer your question, I guess, 10% brightness difference is fine
but the circle edge should be well demarcated. The housing for the
flashlight will be in a 30mm dia. tube. And it should throw this
circle of light at a wall 420mm away.

I need to go over your suggestions and see if I can work something
out. Little more explanation may help a lay man like me.

Rahul

.