# LED Strips Without Diffusion: Safe Distance?



## PerryScanlon (Jun 26, 2012)

It seems like a lot of light is absorbed by common diffusers, and they add time and money to a project. I know many experimenters do testing without diffusion when they are using low-power LED's. Anybody know what distance is definitely safe and what distance is definitely not safe? I would think that 10 feet away would be very safe, but having them.... say....right next to your eye would probably not be safe. Maybe somebody here would be able to fine tune that range a bit more... This is for wide-angle 5050 SMD RGB's running at standard 20mA per channel.


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## AnAppleSnail (Jun 26, 2012)

Safe for how long, and for whom? I find that with blue LEDs at lower currents (20 mA) I naturally want to look away before I see the other symptoms of chemical fatigue in my eyes. Blue LEDs give the highest power photons, and might be the most 'dangerous' of RGB. I use diffusers or indirect lighting for pleasantness, rather than eye safety. It's just not nice to see dozens of point sources scouring my eyes.


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## PerryScanlon (Jun 26, 2012)

I agree that diffusion looks much better when looking directly at the LED's. The glowing orbs behind a frosted diffuser are really nice, but it spreads the beam and makes it difficult to illuminate anything or anyone. It would be nice to light up a band playing at a bar when the LED's have to compete with stray light from other areas. Another thought is that in an industrial work environment, LED strips that are above people's heads might work well to illuminate an area if they are not diffused.


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## blasterman (Jun 27, 2012)

You guys would probably freak when you saw my RB XT-Es driving bare at an amp then.

You can mount power LEDs in C-channel, and if you use acrylic optics there's is very little eye fatigue unless you are staring right at them. I've done this for bars and it looks really cool.


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## AnAppleSnail (Jun 28, 2012)

Ooh, stage lights! Think of the lighting environment. In a dark bar, a row of XR-Es can do a lot, especially with optics. If the bar has stage lights (Even a few PAR lights) then you'll need a LOT of color LED to make pretty.


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## idleprocess (Jul 1, 2012)

I wouldn't bother with diffusion on lower-intensity LED strips unless you have some specific concern about children, animals, etc looking into them - especially in common lighting scenarios where the LED's are overhead or not directly visible (ie undercounter).

I diffused some outdoor lighting built around 3-up Rebel LED's running @ 350mA to guard against the outside chance that someone would trespass on my property at night, proceed stare into a fixture long enough to suffer injury, then try to sue me for their own intense stupidity. Given that each LED should be spitting out somewhere in the neighborhood of 100lm, it seemed like a good plan even though I could probably get a lawsuit dismissed on the basis that trespassing and violation of "reasonable person" standards (ie, don't suppress the flinching reflex when you stare at a point source) was required to inflict injury. I certainly spent some time looking at the undiffused product while building and installing the things and suffered no injury.


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## PerryScanlon (Jul 29, 2012)

Thanks for the replies. Decided to sometimes use frosted diffusers, sometimes take them off depending on the situation. I did some calculations, and based on FDA laser classifications, the wide-angle low-power LED's are very safe at normal distances, just irritating to look at. The FDA doesn't account for wavelength, which seems a little strange.


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## SemiMan (Aug 21, 2012)

Look at some of the European specifications. They take into account wavelength.


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## PerryScanlon (Sep 9, 2012)

Thanks, SemiMan. Is this what you were referring to?
http://www.elcfed.org/documents/CEL...y_LED_lighting_Final_1st_Edition_July2011.pdf
Page 15: "Blue light, small source" 1 W/m^2: low risk, 400 W/m^2: moderate risk

If the link doesn't work, it's off this page:
http://www.elcfed.org/2_resource_publications.php
"ELC CELMA Position Paper on Optical Safety of LED Lighting"

Here's what I've been working on if anybody wants to check it out:
http://www.youtube.com/watch?v=UX-AvLz2g7g
http://www.youtube.com/watch?v=s5dDAbsEj1U
That's with diffusion. In theory, I reduced the reflective loss by painting the inside white.


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## Anders Hoveland (Sep 10, 2012)

There are special types of difusers available for avoiding excessive beam spread:
http://www.newport.com/Light-Shaping-Diffusers/141131/1033/info.aspx


I have seen some LED strip lighting that use long piece of shaped clear plastic to spread out the light while still mostly keeping it directional. The plastic acts as a lens, at least in one dimension since the strip is linear. 

This is probably similiar to beam expanders.






In this case, however, it would seem to be a cylindrical single-lens expander.


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## SemiMan (Sep 10, 2012)

Specifically EN‐62471 which is referenced in this article. I know I have read articles and calculated figures w.r.t. eye safety and LEDs, but not for many years so I doubt I would be much help. I would not be surprised if one of the major LED vendors had information w.r.t. this.

Semiman


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