Injecting IR light into LED LCD back-light
Posted: 11 December 2010 09:19 PM   [ Ignore ]
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Has anyone experienced with putting infrared lights around one or more edges of an edge-lit back-light? Or adding white LEDs to increase brightness?
Edge-lit backlights that I have opened so far all have two or three free edges that we could potentially use to do our own illumination. In theory this should work just like DSI except that no Endlighten would be needed. Plus it makes it possible to use other surfaces such as glass for touch surface, ideal in coffee tables etc. Any thoughts before I attempt this?

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Posted: 12 December 2010 08:55 AM   [ Ignore ]   [ # 1 ]
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Would be a good idea but i think you will have the same problem as with other lcds. If you place the IR strips behind the LCD it has to go through the lcd 2 times before the camera can detect it.
1st time up through the lcd to your finger and the reflect back down through the lcd. So you loose quite a lot of IR because the polarizers of the LCD block it.

In normal LCD setups you also loose quite a lot of IR but it only has to travel once through the lcd.
So i think it will not work good enough but maybe you have luck with your lcd and it’s worth trying.
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Posted: 12 December 2010 03:38 PM   [ Ignore ]   [ # 2 ]
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Thank you for your comment payne86. I think you have a really good point here. Since I have to take the back-light reflective layer off to enable the camera to see through it, I might end up with more infrared coming directly from the back-light than reflected from the finger, which would not be good. Nevertheless, I give this a shot since I couldn’t find any reports on this in the forum. I will report back next weekend.

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Posted: 13 December 2010 10:40 AM   [ Ignore ]   [ # 3 ]
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I dont think it’d be that much of an issue, mainly cause for one thing MS thinsight does the same thing sends ir from behind the LCD and then detects it and 2) LED edge lit displays don’t output near as much ir compared that to ccfl back lighting since they are LED i would assume it would be close to 0 if anything.

But as Aras pointed out you would have to remove the reflective layer from the back light now what that would do is decrease your brightness and that i can see being a bigger problem then IR fading

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