Collimate Light from an LED | Thorlabs Insights

Collimating light from an LED or other large, incoherent source can be a surprisingly challenging task. The emitter’s size and the collimating lens’ focal length and numerical aperture (NA) all influence the characteristics of the collimated beam. It can also be hard to know when the lens is positioned optimally. In this video, two lenses with different NAs and focal lengths are used to demonstrate a couple of collimation approaches. In addition, the emerging image of the emitter and other typical features of beams provided by collimating lenses are explored.

Two significant collimated beam properties are divergence and optical power. As shown in this demonstration, when two lenses have the same diameter, more light is collected when the focal length is smaller, since the NA is larger, but at the cost of increased collimated beam divergence. The divergence is also affected by the light emitter’s physical size. Assuming the same lens is used, the collimated beam’s divergence is larger when the emitter is larger.

One consequence of a larger divergence is that the beam’s irradiance (optical power per area) decreases at a faster rate with increasing distance from the lens. Another consequence is that the collimated region is shorter. The collimated region can be described as the part of the beam where rays from across the entire emitter overlap, which is usually close to the lens. With increasing distance from the lens, divergence separates the rays into different bundles, according to their point of origin, revealing an image of the emitter. Seeing an image can be unexpected, since it is not predicted by the thin lens equation and can create unexpected artifacts in an application.

00:00 - Introduction
00:41 – Divergence & Collimation Overview.
03:28 – Collimation with 0.76 NA Lens
05:50 – Collimated Beam Features
06:46 – Collimate with 0.24 NA Lens
08:34 – Collimated Beam Features

Components used in this Demonstration Include:

[ronaldnonnenmacher]

Would there be an expected approach on what relative value of NA to use if the goal was to send a modulated light beam from an LED a significant distance eg 100 feet? Would a smaller NA having lesser divergence produce more intensity at a distance than a larger NA lens that diverges more?

[ParTaban]

Hi
your video is great but there are some contradictions:
it is concluded from this video that a lense with higher NA and therefore with higher divergence, should provide lower irradiance as the beam area increses and the power decresea.
but when you strat to explain experimentally, the results is vise versa.
for lense with NA = 0.76 and f = 32 mm, irradiance is 177w/mm2, p = 0.29w and A= 1640mm2
for lense with NA=0.24 and f = 100mm, irradiance is 17w/mm2, p = 0.03w and A= 1735mm2
can you clarify this? do we expect a decresead iradiance with an incresead divergence which should be obtained wiht lense with NA = 0.76?

[brittanywright]

I'm looking to increase headlight output by both distance and width. What would be the best way to achieve both?

[ZozobraDoom]

Great video. Could you give an overview of how to focus an LED for fluorescence spectroscopy applications? Would a generalized approach be to collimate the beam and then focus this beam? My issue is that a lot of high power UVC LEDs aren't really that high power and have 130° viewing angles - ideally I'd be trying to get as much power into a 2-3mm^3 sampling area.

[뺚Ppark]

Is a bi-convex lens suitable for collimating LED light?

[chimpdongs]

Can you do a video or explain how to collimate the light from multiple LED point light sources? E.g. in this example you had 4 beams in a square 1 inch apart, I assume you have to gather and condense all the beams into one spot and then collimate it, but its so complicated.

[ahmedmostafa-tfvo]

Can this setub used to collimate light from a small filament lamp ?

[Tferdz]

Maybe some optical tweezers setup later? How to align with scattering collection?

[Abrar-hc]

Your explanation is excellent, but I could not understand well