Lens Question for Design of an Infrared Spotlight

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Discussion Overview

The discussion revolves around the design of an infrared spotlight intended to illuminate distant objects for visibility on an IP-enabled night vision camera. Participants explore the challenges associated with lens selection, particularly focusing on the use of off-the-shelf plastic lenses and the requirements for effective light focusing over a distance of 400 meters.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant seeks advice on using LEDs and optics to create an infrared spotlight, specifying the need for a compact design within a 2m PVC pipe.
  • Another participant asserts that plastic lenses are not suitable for infrared applications due to IR transparency issues.
  • A different participant questions the claim about plastic's IR transparency by referencing the functionality of TV remote controls, suggesting that some plastics may allow IR transmission.
  • Some participants propose using narrow beam angle LEDs as a potential solution, indicating that this might eliminate the need for additional optics.
  • There is a discussion about the specific wavelength of the LED (850 nm) and whether typical plastics are transparent in that range, with conflicting views on the availability of IR optics in plastic.

Areas of Agreement / Disagreement

Participants express disagreement regarding the suitability of plastic lenses for infrared applications, with some asserting that they are not viable while others question this assertion based on examples. The discussion remains unresolved regarding the effectiveness of using plastic lenses and the appropriate LED specifications.

Contextual Notes

Limitations include the lack of consensus on the transparency of plastics to infrared light, the dependence on specific definitions of IR transparency, and the unresolved question of the necessary power output of the LEDs for effective illumination.

Who May Find This Useful

Individuals interested in optics, infrared technology, LED applications, and DIY electronics projects may find this discussion relevant.

zlj06
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Hello All.

I'm working on a project to build an infrared spotlight which will hopefully light up a distant object so that I can see it on an IP enabled night vision camera. The lens problem seems very straight forward, but I could use some help. Per the attached diagram, I want to focus the light from an led (or cluster of LEDs) on an object that is 40m tall, 400m away. Ideally, I'd like the LEDs + Optics to be housed in a piece of PVC pipe less than 2m long. Whats the easiest way to do this with off the shelf cheap plastic lenses?

Thanks for the help...
 

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zlj06 said:
shelf cheap plastic lenses?
IR transparency and plastic are mutually exclusive.
 
I'm not an expert but I suspect you will need more power than that type of LED can produce. How sensitive is the camera? Perhaps start with that and work back?

Perhaps you could use LEDs that have a 6 degree beam angle? No optics needed then.
 
Bystander said:
IR transparency and plastic are mutually exclusive.

You might have to explain that. How do TV remote controls work if (at least some) plastic isn't IR transparent.
 
CWatters said:
You might have to explain that.
Just googled IR optics, and no plastic components.
 
zlj06 said:
Great call CW! That's a much easier solution. Digikey has some very narrow radiation angle LEDs, so I'll solder together a cluster of those first and give that a try. Thanks, Zach
Bystander said:
Just googled IR optics, and no plastic components.
The LED in question is in the near IR, at 850 nm. Aren't plastics typically transparent there?
 

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