looking for LED filter plastic

"Phil in Melbourne"

** If your leds are not bright enough to work in bright sun - then you are stuffed.

Get brighter ones.

....... Phil

The only thing that came to mind was this

Circular polarizer films.

D from BC British Columbia Canada

Why not buy some dark red 3mm sheet glass from the nearest stained glass hobby supplier?.

Yes, and no. The problem is with sun glare. If the sun shines on the LEDs directly, it looks like they are lit.

If a filter is used, it should increase the contrast between leds that are off and leds that are on.

Thanks D, that looks promising.

"Phil in Melbourne"

** That is a result of the sunlight being brighter than the LEDs are.

A coloured filter will not help.

** All a red filter will do is help darken the background - painting it matt black is the most effective way of achieving that.

BTW:

How about you say JUST what it is you have and what you are trying to achieve with it..

So far it looks like something that is not possible.

....... Phil

If you have a small viewing angle, you can use that stuff that 3M makes that looks like a bunch of slats. They usually sell it to keep people for reading your laptops screen from the side. If you rotate it 90 degrees, I will keep sunlight from above out of the display.

Circular polarizers like used on LCDs work well to keep sunlight from going in and then bouncing back out.

Don't use a filter witht he same color as the LED. They make matters worse by coloring and reflecting sunlight.

A lot of improvement can be had by careful design of the placement of the lens and a shield above it. You can also tilt the lens down so that any sunlight is reflected down to the ground and the users line of sight is reflected to the darker ground by the lens surface.

Ignore the makers claims. LEDs really come in three brightness grades (1) Are you sure you turned it on (B) Way too dim and (iii) Just barely bright enough.

Ship a set of those disposable paper sunglasses the eye doctors give you when they dilate your pupils with the product. :)

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I must be buying good ones- we had a complaint that the display was

*too* bright, even though the requirement stated "sunlight readable" as a "nice to have".

Best regards, Spehro Pefhany

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"Phil in Melbourne" wrote in news:47e31bbb$0$8090$ snipped-for-privacy@news.optusnet.com.au:

Various kinds of filters work, even some that actually attenuate the light from the LEDs themselves. There are several phenomena that work in your favor:

1) The ambient (e.g., sunlight) light reflected by the LEDs and other objects inside the filter has to travel through the filter twice, once on the way in and once on the way out. A filter that absorbs 50% of ambient light will transmit only 25% of light reflected from inside the filter. So, almost any kind of absorbing filter (e.g., 'smoked' Perspex) improves contrast somewhat. 2) Colored filters selectively absorb ambient light, and the human visual system discriminates more on the basis of local contrast than on the basis of absolute brightness. Color contrast filters also do the double filtering trick described in 1. 3) Louvered bezels and micro-louver materials such as 3M Light Control Film are strongly absorbing from most directions and highly transmissive in the desired viewing direction, These materials are used to control the visibility of traffic control lights, among other applications. 4) Polarizing filters can be oriented to selectively absorb ambient light.

The right combination of filters will allow you to see relatively dim LEDs in strong sunlight. However, these days designers often simply choose high brightness LEDs and crank up the drive current, if ample power is available.

Paul Mathews

Ha! You made my morning! (PST)

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I was looking at some traffic lights today. I don't think the LED versions use any filters.

Yes they do. The Aldridge ones (most common) have a domed filter of the corresponding colour in front of the LED arrays, they are however rather light and a not diffused nor are they designed as a lens as such. In traffic lights this is not so critical as in a large sign, since the traffic light arrays have shades over them. I have done work with them in the past and can tell you they are VERY bright. I can't remember the mcd rating but each different colour array has a different number of LEDs to compensate for the differing brightness of each LED / filter combination so the total light output from each array is the same.

Regards James

No, you just had a whiny customer and the display for once wasn't dim enough to whine about it being too dim, so he had to whine it was too bright. Did he also complain that the color clashed with his shirt?

You can always dim them by PWMing the drive.

If you get off angle to them, you will see very little light. They use directional lensing to shoot the light at the drivers. The same lensing keeps sumlight out of the LED so it can't reflect back.

It also helps keep the drivers on the cross road from seeing the yellow light and jumping the red before it turns green.

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"Michael A. Terrell" wrote in news: snipped-for-privacy@corp.supernews.com:

Ah, an excellent source. Thanks for letting me know. Free/open news service are getting hard to find these days.

GB

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I meant no color filters. The unlit LEDs looked milky white.

Moosefet and Paul Mathews referred to a type of lenticular filter film which restricts the transmission of light to some angle either side of

90 degrees. Rear projection TVs also use a lenticular layer, and I have some pieces of that if you want to try it (I'm also in Melbourne, and have a snipped-for-privacy@gmail.com email address). The material I have is made from threads of glass fibre laid parallel on a film adhered to a 3mm plastic sheet. A regular source would be expensive, unless the 3M film is available at a decent price. Just email privately and arrange to drop by.

Clifford Heath.