Homemade LCD backlight??

[Buriedcode]

homemade backlight

Hi,

I've got a few nokia displays, and some generic LCD panels, and I'm thinking about making my own backlight, since buying them is terribly expensive, and its hard to find exact sizes (well, enough to cover the panel, but not too much).

I'm not into EL, or CCFL, just LEDs, these are cheap, available in many colours, easy to drive, and are in many shapes (rectangular, SMD etc..).

The nokia LCD's (3310, 3210, monochrome ones) use LED's on the PCB to backlight (side light), with the plastic keypad frame as a light guide, with a white sticker underneath. This seems to work, but wastes a lot of light (used to light the keypad as well). The leds are not 'under' the LCD, they are facing upward, and the plastic frame covers them, curving at a right angle going under the LCD.

I was thinking of using some clear acrylic as a sort of light guide, but its difficult to polish for reflecting surfaces, for internal reflection, so could I just use some mirror tape, or metal foil? OR would 'white tape' be the best option?

I was hoping that, for side lighting, I could simply mirror three sides of the plastic sheet, and the bottom, then place some sort of diffusing filter over the top, and wack it under my LCD. I could make a small plastic housing for SMD leds that clips on the un-reflected side, and makes sure all light goes into the plastic. Also, maybe 'roughen up' with a file the bottom surface, before putting on the foil, to scatter reflections all around the panel.

Also, the 3310 LCD (without the keypad housing) has a silvery film over the bottom, which lets 'some' light through. I personally think this is a reflector, and I've read that to add a back light, the reflector must be removed, and placed under the backlight (so the BL is sandwiched between LCD and reflector). But why would nokia place the reflector between the BL and LCD? Unless of course its simply a polarizing filter, but its like tarnished silver.

Sorry for the long post, but ANY idea's/experiences with LED backlighting, light guides, diffusuers would be welcome. I find it hard to believe that making an effective cheap BL is so hard.


Thankyou,

BuriedCode.

 

[techie]

homemade lcd backlight

I have used diffusers in the past. Basically you have a kind of transparent epoxy that is mixed with a powder diffuser to make the matterial . This is a special matterial since it creates a glow inside it when light enters it anywhere.

 

[Buriedcode]

how to make a homemade laptop backlight

Hi techie, thanks for your reply.

As I'm going true DIY on this one, I'm gonna have to improvise. Anything is better than nokia original design.

Its interesting to hear about how they disfuse the light. I suppose it can't to try mixing up ground glass in some strong epoxy resin (clear setting, thing I have some) and then use this to sandwich two pieces of clear plastic.

Unfortunately, buying a 'transflector' isn't really an option. So it looks like I'm gonna have to go with a 'transmissive' display Unless enough light gets through the reflector on the back of the LCD.

Thanks again.

BuriedCode.

 

[techie]

nokia 3310 lcd backlight

This ground glass doesnt seem to be a bad idea. Do keep us posted if you have any success.

 

[Buriedcode]

homemade led backlight

Hi techie.

You said to keep you posted

Well, I think I've abandonded the 'side-light' idea. I cannot seem to get enough light out of it, although I am using a single 3mm 2000mcd red LED for a test, hardly suitable since most of its light escapes either side of the plastic panel. And I cannot find any 'light guide panels' that fit the size of my LCD and have a suitable stucture (they all look the same as the original Nokia design for the backlight - bit weak).

Because the LCD is square, I suppose I could use either (side-lighting and under-lighting) but I'm going for under-lighting, with an LED array, inside a small white plastic housing, with a diffuser over the top. Thats what my 16x2 LCD module has, it has a total of 10 LED's, each with a pathetic light output, but togehter, along with the diffuser is more than enough, And it beats side-lighting hands down.

So, back to the drawing board. The diffuser.
I couldn't find any ground glass, and my epoxy dried up I've tried many house-hold things, plastic bags, various papers, plastics etc... but none spread the light enough, or they do but they only let through about 10% of the light. Getting hold of standard (16x2, 20x2 etc..) LCD backlights is tough, and even tougher to find the diffuser material they used.

Thanks for the epoxy idea, as soon as I get some, I'll give it a whirl. In the meantime... have any other idea's? I also want to have RGB LED's, so it'll have to mix colours as well. I posted something about that in the 'optics' forum:



Cheers,

BuriedCode.

 

[Buriedcode]

3310 lcd backlight

Hi again, long time no post....

Well, I put the backlight idea on hold for a while but now I'm back into it. I've got some RGB LED's (6 lead PLCC ones) which are fairly high output (500mcd @ 120 angle) and they mix the colours really well. But, because they are so big and expensive, mounting them in some osrt of 'array' would cost way to much, and it would be about 15mm thick.

So.....Its back to the 'edge-lighting' idea. I would like to know peoples suggestions/experiences on the lightguide. Basically, I'll use 2 LEDs shining into the side of clear perspex/acrylic, I might have a diffuser (some translucent drafting paper from a local art store, brilliant stufff) on the top. Now, I've sdone some extensive research on this subject, but few people have made they're own backlight unit.

I've experimented with various methods of extracting the light from the plastic. Sanding, 3M micropore tape (the best so far) and gluing frosted plastic to the acrylic. Anyone have any more suggestins?? I'm planning on getting some small acrylic tiles to do some tests and compare the results. Also, I think that 3M's scotch magic tape™, the translucent stuff, would be good. Tapes are a great idea, the glue optically couples to the acrylic, simply pressing a film against the plastic would do nothing since we need to disturb the total internal reflections.

As I said before, this is true DIY, I have no special equipment for forming acrylic, but I refuse to make something thats inefficient. I'm confident that 2 RGB LED's are enough to light a 40x30mm area at 10000CD/m²+.

Comments/suggestions/criticisms welcome...

BuriedCode.

 

[techie]

diy lcd backlight

10000CD/m2, that is a lot brighter than the sunlit daylight. !!

 

[Buriedcode]

home made lcd backlight

10000CD/m2, that is a lot brighter than the sunlit daylight. !!

Whoops! Added one too many 0's there. 100000mCD/m². Basically I'd like it to rival the surface view, COB (chip on board) backlights, although I'm not that hopeful. The nature of LCD's menas I will always lose 50% of the light anyway due to the rear polarizer, maybe 3M's DBEF film would sort that - if they answered my emails.

I'm getting a tad obsessed with this, but I don't think any amateur/modder on the web has performed any experiments with LED backlights, so I'm taking the challenge.

Cheers,

BuriedCode.

 

[Buriedcode]

lcd backlight diffuser material

Hey, I know this thread is a bit 'dead' but I've just had another idea....

Glitter gel pen. Hopefully, if painted on the back of the acrylic, the 'gel' (when set) will optically couple to the lightguide and the glitter fragments will reflect light up out of the lightguide. I could add more layers the further from the LED to make the whole thing nice and even. Its pretty similar to the 'white dots' you see on TFT monitor backlights, which apparently are woefully inefficient, but glitter is very reflective, and the small particles would never be exactly parallel to the lightguide, so we would get many angles of reflection, but all generally 'up' out the acrylic.

Its interesting, I've seen many different backlight designs (for side lighting) and all of them seem pretty inefficient to me, even the new 'microprisms'. I'm aiming for 200-250 nits, which is roughly what a 'surface' backlight produces.

I'm confused as to why no-one seens interested, given all the new 'case mods' about for PC's. A small light panel that can change colours would loook pretty smart on my comp

cheers,

BuriedCode.

Ps. I'm working on an 'etched type panel, edge-lit, but instead of permenantly etching it with a fancy design, I'm hopefully going to use liquid crystals in a polymer, so the 'etched design' can be changed, or even move like video. But, phillips stole my idea they released a headline a few days ago about the new display.....grrrrrr....

 

[Buriedcode]

bright led lcd monitor backlight diy

Hey,

Just thought i'd finish up this topic with some results

Generally, the lessons I've learned for making a backlight/panel light are:

- Use LED's with wide angle, preferably 120+ degrees. Narrow angle LED's are not good for even illumination.

- Use 'sandblasted' vinyl and just stick it to the lightguide. Alone, it doesn't do that much, but with a reflector on the back, and a diffuser on the front, its actually very efficient at extracting light.

- If the lightguide (acrylic, plexi) is to be sanded (instead of above vinyl), the sanding must be done in straight lines, 90 degrees to the direction of the light. - this actually proved to be brighter than comercial edge-lit backlights, which were sanded (or moulded) in all/random direcitons). It may not be even illumination, but thats what the diffuser is for.

- If possible, get hold of a TFT monitor backlight. With the prismatic films, diffusers and reflective polarizers - you can light a 3" x 4" LCD, with three(!!) LED's, running at 20ma each.

I've probably spent to long, and too much money on researching this. But its nice to be able to make small (and extremely bright!) backlights that take hardly any power, and are thin. Way better than EL foil.

I think I'll make a frame for some acrylic paintings I've got. They're awesome when backlit.

BuriedCode.