I need to collimate light beam of an LED (white light) using a plano convex lens of focal length : 75 mm. If I place my LED at the focal plane (focal point) of the lens, will the lens collimate the beam of light from the LED or not? If the plano-convex lens does not collimate the beam fully, then what type of collimation will it be called as?
If you put a naked LED, at the focal point of the lens, you will obtain a collimated beam, with a small divergence d = arctan(D / focal length), where D is the size of the LED's emission surface. But, if the LED is immersed inside a diffusing plastic package you will have a more divergent beam, since you should consider, approximately, the size of the package for D. Finally, if a small lens is already mounted in front of the LED, (microlens are usually packaged together with the LED to narrow the angle of emission), you will need to reduce the distance between the LED and your lens, respect to its focal length, to achieve a good collimation.
Thank you Dr. Roberto for your response.
That means putting the LED at the focal point of the plano-convex lens will do the job of getting good collimation?
You should also take care, that the plane side of the lens is orientated towards the led. This reduces aberrations.
The use of the adjective "good" is very relative here. Only arc sources are close to being point sources. The science behind building a condenser system to image a lamp filament onto a small aperture and then capture the emerging rays on the other side into an achromatic doublet is well know. Depending on the focal length and f/# of your PCX (in your case 75mm ) you could end up with very little light left that is parallel to the optical axis. A shorter focal length aspheric lens might be a better choice. Here is a link to tutorial from Edmund Optics on how to collimate an LED.
http://www.edmundoptics.com/TechSupport/resource_center/downloads/published_articles/prototyping-illumination-systems-photonik.pdf
What LED source are you using? I was able to focus most of the light using a half-ball lens from EdmundOptics
https://www.edmundoptics.com/f/igh-ndex-alf-all-enses/13677/
It gave me almost collimated beam, which I then tight focused using a 5x objective (EFL 40mm).
You can also play with this online simulator, and see that a point source+half ball combination can give you a nice collimated beam https://ricktu288.github.io/ray-optics/simulator/
Mr. Ten's solution of using a ball lens is a good option as they have very strong curvature for gathering low f/# rays from optical fibers. The strong curvature also introduces strong aberations. Not objectionable for single frequency narrow band sources but could be bothersome in a "white" light design as described in the original poster's inquiry, " ... I need to collimate light beam of an LED (white light)..." Since most white light LEDs are either based on fluorescence, which are highly non-directional or on a composite of LED chip (R,G,B) which again can be at slightly different locations and orientations, the simple, single lens may not be a good solution. Even Mr. Ten reported that he had to follow-up the ball lens with a second imaging 5X objective lens system.
Anyone has experience with collimated UV light sources? Any hint about commercially available lamps or the like with those characteristics? Thanks in advance.
Hi Guys,
is it possible to remove the microlens from LEDS in a reasonable manner?
hi guys,
In my case I am using aspheric condenser lens which has NA of .61. but still i haven't got proper collimation. could please suggest some other solutions for this!
thank you.
I would like to ask Timour Ten about his answer. I am using a high power LED (4.5W) and need to couple the light into a bundle of fibers with reasonably good uniformity. I have been using a lens from Carclo but while it does a great job of capturing the light from the LED it is not very uniform. I have started to play with half ball lenses and they provide a much better uniformity of light. However, I cannot remember enough optics to make the best choices to get the beam down to 9.5mm in diameter. Any help here would be much appreciated.Thanks so much.
I haven't tried it myself, but Danny Rich (see answers above) posted a link to EdmundOptics review on possible solutions, which I am reposting here: https://www.edmundoptics.com/globalassets/knowledge-center/articles/prototyping-illumination-systems-with-stock-optical-components-en.pdf/
where one of the solutions is to use a microlens array, which to me makes total sense, since the LED is a pixel array, and you want all these "point" sources to be focused, or collimated simultaneously.
With the half-ball lens, I was able to "capture" most of the diverging light from the LED and redirect it onto a pinhole with majority of the power having the same divergence near the pinhole. The pinhole is then my new "point" source and I measured the divergence after the pinhole and picked the lens that I needed to image whatever the pinhole has on the sample cuvette. So it looked like something like that (attached picture)
- Badges
- Science topic
- Similar topics
- Computer Communications (Networks)
- Simulators