Physics Help Forum Creating a parrallel lightbeam.

 Light and Optics Light and Optics Physics Help Forum

 Aug 28th 2019, 10:05 AM #1 Junior Member   Join Date: Aug 2019 Posts: 25 Creating a parrallel lightbeam. Hi, By using multiple lenses, I want to create a parallel beam out of a 100W led. First some thing to show what I understand and have practiced. With a point-lightsouce one can easely create a parallel beam by using 1 lense. I've worked on beamers and managed to create 1 completely by myself many years ago. OK! The thing is, the led is not a point lightsource but the light comes from an area, say 20mmx20mm or even bigger 25mmx25mm, and contains say 100x 1W led. So there are many led's, spread over a surface and each led has a beam angle. What I allready did and what is lots going on on the internet, is just put a collimator/condensor a bit above the 100W led and the light is allready more compact. But still has a very wide angle and a lot of light is lost beside that angle. I allready find out that it will take al least 2 or 3 lenses ( with practical experimenting and software ) tot get an parallel beam or at least a very narrow angle beam. The software gives a nice picture of behaveiour of the lens it diameter, forcu point, position etc! The yellow line indicates the surface of the led. Don't mind the stuf at the left side of the yellow line.This is just to 'create' the led ( surface and light outgoing in an angle. The lensens in the picture are the lenses I also use in practical. I have allready some lenses avaiable, and I think I'm very close to the sollution... Can anyone give me a good dirction how to aproche this parallel beam problem? Thanks in advance! Attached Thumbnails
 Aug 28th 2019, 12:28 PM #2 Junior Member   Join Date: Aug 2019 Posts: 25 I'm thinking to replace lens 1 for a bigger one and at more distance from led. I quess that's a good new aproach...
 Aug 28th 2019, 07:59 PM #3 Senior Member   Join Date: Apr 2017 Posts: 506 I've got a strange fascination for leds ... especially high power ones , my work shop is full of all types , and I've tried what you want to do ... 100W leds are very cheap ... you can make a devastating strobe , many KWs quiet easily , and no need for heat sink since it is off more than on when strobing .... Heat sinks are usually very important and cost more than the led itself ... But the bad news is , what you want to do just cant be done ... no matter what lenses you use , or how you arrange them you won't get parallel... It's all about getting as close as you can to a point source ... the most power from a small emitter This is the best that's available ..... It's 15W and the emmiter itself (yellow ) is only about 4 x 4 mm ... that gives a much better power density than a 100W .... these are used in zoomable touches and can be focused to give a very intense light .... You can increase the diameter of the lens , this will help but then things get too big ... One possibility is to get many torches and fix them together aimed parallel ... Last edited by oz93666; Aug 28th 2019 at 11:42 PM.
 Aug 29th 2019, 02:29 AM #4 Senior Member     Join Date: Jun 2016 Location: England Posts: 998 My first thought is tha each LED in the array needs it's own lens. Each lens would have to be asymmetric and tailored for the position of the LED in the array, such that the focal points of each of the lenses would be at the same point. However you could probably achieve a sensible approximation using a suitably shaped (aspheric) lens at position 1. The focal length of this lens would have to vary between the centre and the edge of the lens. But, I have no idea where you could get such a lens. __________________ ~\o/~
 Aug 29th 2019, 04:12 AM #5 Junior Member   Join Date: Aug 2019 Posts: 25 oz93666Woody I understand! Perfect situation is a light as pointsource. With bigger lenses, the surface wil be much lower in proportion to the lens than the current situation: 20mmx20mm in proportion to a 40mm diameter condensor/collamitor. See if I can find out what the angle is of the led. Defenitly I'm going for bigger lenses. Lucky, got something around here, from (CRT-)beamers! I don't want to buld a portable torch. Just a nice beam straight up to the clouds for a party or 31the december...
 Aug 29th 2019, 04:24 AM #6 Senior Member     Join Date: Jun 2016 Location: England Posts: 998 Freznel Rings If you use a Fresnel style lens at position 1 you can perhaps get 2 or 3 Fresnel lenses of differing focal lengths, one to focus the central portion of the array one to focus the outer portion of the array and one in the middle. These could (with some care) be cut into concentric rings such that the outer ring focuses the outer portion of the array, to your chosen focal position the central ring focuses the central portion of the array to the same chosen focal position and the middle ring... __________________ ~\o/~
 Aug 29th 2019, 04:49 AM #7 Junior Member   Join Date: Aug 2019 Posts: 25 Here, they use a 30W led. These are smaller than the 100W, but still have a square what emmits instead of emitting from a point. We wil l see... Attached Thumbnails
 Aug 29th 2019, 04:51 AM #8 Junior Member   Join Date: Aug 2019 Posts: 25 Wait, there's a previous reaction waiting for aprovel. ( no problem )
 Aug 29th 2019, 10:02 AM #9 Junior Member   Join Date: Aug 2019 Posts: 25 Woody That Freznel idea sound nice! Have some laying around. But instead of using Freznel lenses with different focuslengts, I could use 1 lense, cut out some rings from inner to outer and stack them in the right way. One could place it in 1 of the stages of the lenses setup. The "earlier" thew more acurate it must be. As the "output lens" it can be bigger constructed and a minor mistake has not that big impact as it would be in case it was placed at the lightsource. OFF topic: so nice to see the working and limitations of a spherical lense, at a sudden point, it;s like there is treshhol or something and the ray goes way off. This is were the A-sperical lense come in. How cool is that! Also gonna do some more investigation, again. What is avaiable ( at a reasenable price! ) proberly there a lensen with a focus line instead of point... Attached Thumbnails
 Aug 29th 2019, 10:31 AM #10 Senior Member     Join Date: Jun 2016 Location: England Posts: 998 A spherical lens can focus a parallel light beam onto a point or visa-versa, rays coming out from a point into a parallel beam. If you work it out precisely this is actually an approximation. The approximation is un-noticeable for most practical purposes but can become important for very strong (very fat) lenses. Your problem is that you have light rays diverging from several points which you want to focus through a single point and then on (through more lenses) to produce a parallel beam. A standard point focus lens is based on sections of spheres A line focus lens can be constructed from sections of cylinders. __________________ ~\o/~

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