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How do LEDs evenly backlight an LCD screen?

Perhaps I'm not entering the right search parameters into Google. I'd love to know how LEDs are used to evenly backlight LCD screens, like those used in computer monitors and TVs. How do they achieve even brightness over such a large area? Are the screens edge-lit or lit from behind? Are special lenses required?

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johnny q8 years ago
I'm looking at either making or buying a backlight system for my 42" lcd, so I'm watching these posts with great interest. So far, I've found a few places that sell whole systems or supplies. Here's a place that sells complete kits: http://www.neon-lights.co.uk/
I wish I could find a similar product to their led bars here in Canada, or in the US.
I'm reading up on how these systems are controlled, and powered. I have a small led flashlight here and from the light it throws (mine is one led)_ those backlight bars must be pretty powerful. I notice that leds throw their light thru an angle. I think that would be an important feature in a backlight system. many are 120 degrees. I'm nit sure if a concentrated beam would be better. I figure even 90 degree spread of the beam would be plenty. LEDs come in different brightness ratings, most are 8000 to 15000 milicandelas. (don't shoot me if I didn't get those units right. I'm just going by memory). These are a brightness level, like lumens. If a numger of leds are used together in a parallel circuit, each one must be connected with a resistor, or one of the leds will hog all the juice and the others wuill be dim. I don't know much about these yet, but I will contribute whatever I learbn so anyone posting here should be able to make one.
they do make led replacement kits for florescent light tubes in lcd screen, they last a lot longer and uses less energy, and you'll save on your electric bill well worth the money
Well in handheld electronics at least (after replacing a couple cracked screens), they a lit from the side/s with side firing surface mount LEDs. There are about 4-8 sheets of plastic that the LCD pane sits directly in front of. They usually consist of a piece of silver mylar, a thick piece of plastic with divots on the surface, a thin piece of plastic that has microscopic bumps, and a piece of plastic that has a mat finish. All the sheets of plastic work by dispersing the light evenly. Sort of like how an air bubble coming to the surface illuminates in a pool at night.
Plasmana8 years ago
As far as I know, the LCD screens use florescent tubes to light up the screen. Prove me wrong.
jeff-o (author)  Plasmana8 years ago
Plasmana jeff-o8 years ago
Ahh, Big beautiful LED screen.... Price: $900 WTF!?! Too expensive! :-(
jeff-o (author)  Plasmana8 years ago
It is indeed a premium-priced item. There are others of course, but this was the easiest to find. ;)
Plasmana jeff-o8 years ago
Haha! Okay...
In the past few years, LED backlights have become quite popular especially on smaller displays and laptops. It's a more even light, it's brighter and uses less power. I'm not sure how the light is diffused though. I haven't had the chance to take apart and LED lit panel yet.
Ahh, that is interesting, thanks for telling me!
I believe that they are lit from the side with some plastic that diffuses light very well and may have more than one to have an even lighting, although I believe some are light from the back(Old screens I think)
kmurray248 years ago
I'd like to know this as well. But, I'm guessing that they space them just so the the high brightness areas of the led light meet and some kind of light diffusing plastic sheet. My guessing only...