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I am trying to create a line made from light projected from a lens / guide of some sort onto a surface from a few mm away.

I have used a laser, but comes with safety considerations, space to mount the optics, and a lot of fine tuning.

I was testing alternatives, and had some success using the fibre-optic effect of the edge of an acrylic sheet and some cheap LEDs.

Does a lens or light guide of the type shown below exist?

I am not worried about the "shape" or "geometry" of the acrylic light guide and open to suggestions based on what exists. I am new to optics and need to know where to start Googling! Thanks!

Example

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    $\begingroup$ You should experiment with a plastic sheet sandwiched between two plastic sheets of another material to work as the cladding. Unsure if the sheet plastic with proper index of refraction are available though $\endgroup$
    – DKNguyen
    Commented Jul 6, 2021 at 19:27
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    $\begingroup$ Yes these kinds of guides are commonly used in lighting industry to get the light efficiently into the acryllic sheets themselves because its not always convenient to have the light strip oriented along the obvious edge. Anyway google for total reflection. $\endgroup$
    – joojaa
    Commented Jul 6, 2021 at 21:00
  • $\begingroup$ Thanks, this is super helpful! Do you know what "off the shelf" parts are called? Do you know if they are available with LEDs in them? $\endgroup$
    – John
    Commented Jul 6, 2021 at 23:38
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    $\begingroup$ If the goal is simply to project a line, a round acrylic rod will work as an one-dimensional lens. But it won't do the 90 degree bend. $\endgroup$
    – jpa
    Commented Jul 7, 2021 at 8:15
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    $\begingroup$ @jpa a mirror is really good at doing a 90-degree bend :-) $\endgroup$
    – Carl Witthoft
    Commented Jul 7, 2021 at 13:01

2 Answers 2

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If you have access to a CO2 laser or a makerspace which has one, you can cut the profile of your light guide from acrylic sheet of suitable thickness. You don't have to have the rather expensive thick acrylic, but rather use multiple layers of thinner material. I've "extracted" the profile from your image:

profile extracted

This particular shape would be easy enough to cut from 3-6 mm acrylic, perhaps along with some alignment holes or tabs. The LEDs in the image might benefit from a matching cut-out, to provide a flush surface for attachment.

The laser-cut edges will reflect the transmitted light within the material, while the end "lens" would have to be slightly abraded (sanded) to cause the light to exit at that location.

This type of device may not be available on the market, as it certainly is a project-specific sort of build. It's very much a DIY type of build. I'd be able to churn out this type of guide in less than a day, once the dimensions are made available.

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  • $\begingroup$ This is genius, thank you! I actually have a laser cutter so have spent my evening simulating different "light guide" lens designs using this software ricktu288.github.io/ray-optics/simulator I'm trying to optimise the light projecting out to see if I can do better than a slightly bent sheet of acrylic (forgoing the complicated shape). $\endgroup$
    – John
    Commented Jul 6, 2021 at 23:44
  • $\begingroup$ Why do laser-cut edges reflect light? Is it a property of the material's response to heat? $\endgroup$
    – user20574
    Commented Jul 7, 2021 at 14:53
  • $\begingroup$ The plastic is melted by the laser, which changes the index of refraction for that surface. If the plastic is cut using mechanical means (saw), the edge is ragged, not smooth and creates a "sponge" for the light striking it. Maybe not a sponge, but far less reflective than the melted surface at the cut. $\endgroup$
    – fred_dot_u
    Commented Jul 7, 2021 at 17:46
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The term to search for is 'light pipe'. You may have luck with this question on Electronic Engineering SE (such a part would be part on an EE design).

eg Search for light pipes on Digi-Key.com

While nothing appears to be an exact match to what you're trying to achieve, some of the light pipes shown with wide configuration would come close, although personally, I would use the laser cut acrylic approach suggested in another answer.

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  • $\begingroup$ (i.e. make your own light pipe) $\endgroup$
    – user20574
    Commented Jul 7, 2021 at 14:54

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