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What is a cost-effective way (say roughly $15) to shine a wide but thin beam of light, directly away from the source, so that it would project a line onto a nearby surface?

My particular beam would need to be about 4' wide and maybe 1mm-4mm thick. The light would not necessarily need to be parallel like a laser, but needs to be pretty focused (1-4mm) for the full range between 1" and 4" from the source, so that if an object is moved within that range, the beam projected on it is always thin, and fairly parallel so that ~0.25" bumps on the object would not block parts of the line.

I considered using a strip of SMD LEDs behind an acrylic lense that is concave along the thin axis, and plano (straight) along the long 4' axis, at a distance such that the light focuses to a line in that 1"-4" range...but that would probably be a long focal length, which would require more space than I might have. Also the LEDs would need to be spaced such that the overlap of each LED's contribution makes the line fairly even in intensity. But before going that direction, I wonder if there is a better solution.

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closed as off-topic by Dave Tweed Dec 14 '16 at 19:21

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Laser line projectors are very cheap and range from $2 - $20+ based on power and color. The cheapest are Red, the more expensive are Green or Blue. Some of the power ratings are getting quite high now...for example here's a 20mW Blue with a decent mounting/heatsink and line or cross lens

If you need a white line then your idea with LED's is OK. I have built an edge light using a simple Acrylic rod as the focus element with narrow angle SMT white LED's, but it's really difficult to get a focused line of your size, but it's not bad at 10-15 mm width.

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  • \$\begingroup\$ After doing some experimenting with lens designs using the free OpticalRayTracer program, it looks like your rod suggestion (a circular lens) works very well for projecting a line in short range, which means LED strip is the right component for the job! Having the rod very close to the lights shines a fairly parallel beam roughly the thickness of the rod, and a little farther creates a focusing then diverging line. The laser line projectors look to be best for longer range projection. \$\endgroup\$ – voxoid Dec 16 '16 at 18:50
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A LED laserline will do exactly what do want, and may cost about $15-$20 at your local supplier, or cheaper if you look on eBay or Aliexpress. Really, there's no point in making it more complex.

Here's an example.

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  • \$\begingroup\$ Thanks for your answer. The problem in my case is that the "bumps" would block the line toward the ends of the line where the beam angle is steep (in that example laser it would be 45 degrees), plus a 90 degree or even 120 degree fan angle would not be able to cover 4' in the 1"-4" range. Unfortunately my application does not allow for much more space than that. I'm open to other suggestions. \$\endgroup\$ – voxoid Dec 14 '16 at 19:11
  • \$\begingroup\$ Then use multiple laserlines and align them so the beams overlap. Of course getting a coverage for the full 4 feet while only one inch away is of course a difficult requirement to start with... \$\endgroup\$ – JvO Dec 14 '16 at 19:17
  • \$\begingroup\$ @voxoid. If you use Red lasers (lowest cost), then you could put multiple units on you line to reduce the bump problem. \$\endgroup\$ – Jack Creasey Dec 14 '16 at 19:18
  • \$\begingroup\$ @JvO....great minds... \$\endgroup\$ – Jack Creasey Dec 14 '16 at 19:19

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