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backlight my photo

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PedroV

New Member
I am entering a photo in a contest at work. I want to print the picture on a transparency and display in a shadow box.

That is, I want to have a light behind the picture. I am thinking of a simple switch, battery and about four white LEDs in series, to be housed within. Is there anything else I need to worry about?
 

Sceadwian

Banned
White LED's aren't going to back light a photo very well, they're tiny little spot sources, you're going to need something to diffuse the light. LED's are commonly used for backlights but they pointed from the edges of a sheet of glass with some kind of surface treatment that causes the light to come out from everywhere on the surface. Not sure where you can get something like that.

If you're just using the LED's behind the picture to shoot light to the front you should be fine, just use a really dark backdrop so you can't see the LED through the photo.
 

Tails

New Member
You can also use a cold cathode fluorescent kit (lamp and inverter), It's easy to find in an old Game Boy Advance SP.

If you just have LEDs, you need to spread the light as LEDs shoot a very narrow spot, like Sceadwian said. Also be sure to not overdrive the LEDs, they can get extremely hot and eventually burn out...
 

microtexan

New Member
How large is the photo? A couple of the cc florescent tubes behind a piece of frosted glass will probably work well and no worry about heat.
 

AllVol

New Member
A ground glass pane, or as it was called above, frosted glass, will do the trick. Just aim any incandescent bulb at the glass and the light will be difused evenly.
 

Sceadwian

Banned
One problem with those glow strip mike. They're green.
creakndale This isn't about lightning for photography, it's about lighting a photograph =)
 

Mike_2545

Super Moderator
Well I didn't see the picture pedroV was trying to back light, maybe green is what is best, on second thought, maybe not :)
 
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Sceadwian

Banned

Hero999

Banned
They're not as efficient as LEDs though.

Just use diffused white LEDs mounted behind frosted glass.
 

duffy

Well-Known Member
White leds behind frosted glass still give you hot spots unless they are quite distant. I've tried to get uniform lighting on a panel before, it's difficult. Best bet is to BUY one, or strip it out of an old LCD panel the size you want.

If you want to make one yourself, a good (and flat) technique is to edge-light acrylic sheet (with smooth edges), then apply a graduated dot screen (opaque white) to the face side and a reflector to the back. The size of the graduations on the dots is inversely proportional to the light in that area.

Take a picture of the edgelit panel with the reflector, and use the brightness distribution with a dotscreen filter in Photoshop to make the graduated white dotscreen. The idea is the dense areas of the dotscreen cover the brightest parts, and reflect more of the light energy back into the acrylic.
 

Hero999

Banned
White leds behind frosted glass still give you hot spots unless they are quite distant. I've tried to get uniform lighting on a panel before, it's difficult.
What sort of LEDs did you use? Were they diffused?
 

duffy

Well-Known Member
Yes, I've tried it with diffused. You clearly have not tried this yourself. It is more difficult than most people imagine.
 
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Sceadwian

Banned
I have, Duffy's right it's not easy to get uniform light with an LED. It's virtually impossible in something as small as a shadow box. The edge light acrylic sheet works great. I took apart a scanner that had a backlight for photonegatives and it has a CCFL tube light at the edge and tiny little squares on the top to pull the light out of the acrylic, it had a thin diffusion sheet over the top if it to even out the light more. But the sheet was real small, not sure how practical it is to find the materials for it.
 

PedroV

New Member
Thank you for your many suggestions. I went lo-tech:

Sorry, this might have been more suitable to art-crafts forum than electronics.

1. went to Kinko's... they printed my picture on 8.5x11 transparency. It was a picture of a red-ish flower. (sample photo attached)

2. From large hardware store, I bought fluorescent light (about 5 in. long) that runs on 4 AA batteries. I used cheapo batteries bought in bulk. I was not allowed to use electrical outlet.

3. Instead of frosted glass, went with a sheet of white printer paper. I put the white paper behind the transparency. One sheet seemed not enough and 2 sheets too much.

4. With still too much light, I taped a small piece of colored paper to the front of the light.

5. It was still too bright, so I taped colored paper to the inside back of the shadow box, which was white. The paper had similar color to the subject of the picture.

6. The shadow box was about three inches deep.

It looked great, as the venue was not well lit and my picture stood out among others.

The only regret was that the cheapo batteries wore out after about 4 hours. I should have used longer lasting batteries
 

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Sceadwian

Banned
If you can determine if it used those 4 AA in series or parallel you can use a DC wall wart to power it. I'm going to assume they were in series. That's 6 volts. So find a 5 or 6 volt wallwart supply and use that instead. Just don't use anything over 6 volts or you'll damage the step up converter the light uses.
 

microtexan

New Member
Well done, glad it turned out great. Thanks for sharing the outcome.:)
 

PedroV

New Member
> So find a 5 or 6 volt wallwart supply

For that particular art competition, I did not have access to wall outlet.

But it turned out so nice that I may display it at my home. And do as you suggest.
 
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