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'[EE] Shining light in plexiglass'
2007\09\03@175814 by Jinx

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> IIRC some time ago (years?) someone (Jinx?) was experimenting
> with shining  light in Plexiglas by attaching a led on the edge of the
> sheet.

Gaston,

26th December 2004 (2004 ? Oy !)
[EE] Backlighting panel LCD

http://home.clear.net.nz/pages/joecolquitt/led+lcd.html


2007\09\03@181313 by Gaston Gagnon

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Jinx wrote:
>> IIRC some time ago (years?) someone (Jinx?) was experimenting
>> with shining  light in Plexiglas by attaching a led on the edge of the
>> sheet.
>>    
>
> Gaston,
>
> 26th December 2004 (2004 ? Oy !)
> [EE] Backlighting panel LCD
>
> http://home.clear.net.nz/pages/joecolquitt/led+lcd.html
>
>
>  

That is what I was looking for, thank you Jinx.
Gaston

2007\09\03@225023 by Jinx

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> That is what I was looking for, thank you Jinx.
> Gaston

I've tried a couple of other approaches such as trying to guide
the light with grooves or pits, but no improvement on what I'd
already posted. Don't be put off by the camera flaring. It really
does look better IRL and is quite acceptable IMHO

The problem is, of course, trying to evenly diffuse a point source
like an LED over a short distance from the side. If you have depth
behind the display it does light up fairly well from the back, rather
than from the side. That gives you the option of one or two bright
LEDs like torches some distance back or many smaller LEDs in a
bit closer

2007\09\03@233619 by Gaston Gagnon

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Jinx wrote:
>> That is what I was looking for, thank you Jinx.
>> Gaston
>>    
>
> I've tried a couple of other approaches such as trying to guide
> the light with grooves or pits, but no improvement on what I'd
> already posted. Don't be put off by the camera flaring. It really
> does look better IRL and is quite acceptable IMHO
>
> The problem is, of course, trying to evenly diffuse a point source
> like an LED over a short distance from the side. If you have depth
> behind the display it does light up fairly well from the back, rather
> than from the side. That gives you the option of one or two bright
> LEDs like torches some distance back or many smaller LEDs in a
> bit closer
>
>  
Your results are quite impressive.
My application is not quite that difficult to meet though. A friend of
mine is doing some art work and he would like to include a little
beating hart in it. So your suggestion of lighting from the back is
probably the way to go.
Can you clarify  "some distance back"  do you mean the led is not in
contact with the Plexiglas?  If that is the case how do get the light to
diffuse over the whole surface? Please light my lantern :)


2007\09\04@051316 by Jinx

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> Can you clarify  "some distance back"  do you mean the led is
> not in contact with the Plexiglas?  If that is the case how do get
> the light to diffuse over the whole surface? Please light my lantern :)

The light of an LED is quite spread out at a few cm (depending on
the part's beam angle and lens) and so distance has done some of the
diffusing for you, because each part of the beam is allowed to follow
its own course

Say you've got a glass panel that's 50mm x 25mm and an LED with
a beam angle of 60 degrees. If the LED is 43mm back from the glass,
its beam has made a circle 50mm in diameter. Might be a little dim
at the far left and far right. Two or more LEDs a little closer to the
glass with overlapping beams would probably cover the width of
the panel quite evenly. I believe that's the construction of backlit
alphanumeric LCDs

When you try to capture a beam right at the source, then guide and
diffuse it, the result isn't so uniform, because the guide isn't as uniform
as free space, and light leaks out in the wrong place or doesn't leak
out in the right place. If the intention is to simply move the light from
the LED up to a dot on the fascia, that's easy to do with a rod guide.
Spreading it out evenly over an area is trickier but it can be done
fairly well with a little patience and trial and error with paths and
diffuser materials

2007\09\04@162538 by Hector Martin

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Jinx wrote:
> I believe that's the construction of backlit
> alphanumeric LCDs

Most of the ones I've seen use an array of LEDs behind the LCD, not
lighting from the sides. Cheap digital clocks use side-lighting, but all
the alphanumerics I've seen use array backlighting. There is a piece of
diffuse white plastic in between to even out the light from the LEDs.

--
Hector Martin (spam_OUThectorTakeThisOuTspammarcansoft.com)
Public Key: http://www.marcansoft.com/marcan.asc

2007\09\04@185720 by Jinx

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> > I believe that's the construction of backlit alphanumeric LCDs
>
> Most of the ones I've seen use an array of LEDs behind the
> LCD, not lighting from the sides.

Hector, if you re-read my paragraph you'll see it was about
backlighting, not sidelighting. I've got 3 backlit LCDs running
right in front of me !! ;-)

nz.farnell.com/jsp/displayProduct.jsp?sku=1220434&CMP=KNC-GNZ-FNZ-GEN
-EN-SKU

Most of the LEDs are under the glass, but 4 of them are proud
by 4mm on the right, and the diffuser is also sticking out. Not
sure why they're built that way, perhaps the diffuser has guides,
but light is lost to the front


2007\09\05@055850 by Alan B. Pearce

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>> I believe that's the construction of backlit
>> alphanumeric LCDs
>
>Most of the ones I've seen use an array of LEDs behind the LCD, not
>lighting from the sides. Cheap digital clocks use side-lighting, but all
>the alphanumerics I've seen use array backlighting. There is a piece of
>diffuse white plastic in between to even out the light from the LEDs.

I have a cheap stereo system that used filament bulbs to edge light the LCD
that displays the radio channel and input selections. They must have been
low voltage ones wired in series, and one burnt out after a short time. I
replaced them with a string of orange LEDs salvaged from an old fax machine.
Has been working for something like 15 years continuous.

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