LED Lighting systems for book scanning

[daniel_reetz]

Hope you're all having a great summer, and hope this stirs the waters a bit.

I have been busy researching a third-gen bookscanner, probably incorporating LED lighting. I've read thousands of posts over at candlepowerforums over the last few years, mostly because I love LED flashlights. I want to convert some of that wasted time into a usable lighting system, but things aren't looking good yet.

At the moment, I have 4 Cree Q5 LEDs, and 4 1A drivers. In principle, with that kind of power, I should have around 700 lumens at the emitters, and some fraction of that on the book surface.

It looks like things are not so simple, though. My first observation is that despite the ridiculous current these things are drawing, and the insane heat they are producing, they are not actually that bright. Now, if you put some kind of focusing lens on them, they are very bright, because the light is concentrated in a small area. However, for this application, that won't work, because we need diffuse, even light. Another potential problem is that the current draw rises with temperature, probably causing the luminous output to droop.

It would be possible to get relatively even light if you were using many, many LEDs and some optics, but that would be expensive. The cheapest you can do one LED&driver combo is about $8, and each one draws 1 amp, so you're looking at a 16 amp, 5V power supply, and the necessary heat dissipation, and so on. There might be a better, cheaper way to drive them. I will be consulting with my friend Wolfgang, the ELECTRONICS GENIUS, about this.

For now, I'm just going to post a bunch of pictures here. We have a very nice photometer at work (a Minolta LS-110), and I'm going to measure the actual luminous output of the halogens I'm so fond of and compare it to the luminous output of these LEDs.

[daniel_reetz]

Just wanted to note that my primary motivation for using LED is portability; if they don't work out, I'll be following in Rob's footsteps and using FOUR HUNDRED WATTS OF POWER.

[kentsin]

LCD screen backlit?

[daniel_reetz]

LCD screen backlights are usually fluorescent, fragile, and not very bright. At work, I disassembled an LED one for a mini-display, and the total luminance was only a few hundred CD/M^2.

[kentsin]

I read from Atiz they use led also.

I still waiting the frame of my scanner build from the hardware store. They are not very happy with my original design, and they talk and talk to me again and again wanting me to change it.

I have the light bulb from the photo shop, I think they are very hot and bright which I do not like.

If you can come up with the led solution I think I will follow.

Btw, how bright is necessary for a bookscanner to work? I have some leds laying around and can order some from China through taobao.com if necessary.

[Turtle]

Try Xenon HID arc lamps like this one used in car headlights that runs off 12V. Some probably can run off 9 volts so it can be portable.



quoted from offroad-adventure-travel.com

Compared with fluorescent and incandescent lamps, HID lamps produce a far higher quantity of light per unit area of lamp package.

HID lamps produce light by striking an electrical arc across tungsten electrodes housed inside a specially designed inner fused quartz or fused alumina tube. This tube is filled with both gas and metals. The gas aids in the starting of the lamps. Then, the metals produce the light once they are heated to a point of evaporation, forming a plasma.

check out this youtube video HID small desk lamp. It can blind you.

http://www.youtube.com/watch?v=bQsJh7ssifE

[xylon]

i like how small it is. do you think it produces less heat then spot lights would? i can't read the text on cinder block. (joking)

[Cabe]

I would caution against HID bulb systems for 2 reasons.

1) HID (High Intensity Discharge) uses essentially a spark to produce light this gives off UV which the headlight glass blocks, although UV light is dependant on there being mercury vapour present in the gas mix.

2) To produce the spark you need a ballast which can produce AC voltages usually around the 85v mark, having said that if you are competent electrician and happy working with mains AC that shouldn't be a problem. However I know of no "turn key" solution for driving HIDs from a home supply, unlike halogens which can use standard lamp holders.

If you can overcome these then bon temps all the way as they are an excellent and efficient source of good quality light.

[kentsin]

http://item.taobao.com/auction/item_det ... at=0&pm1=1

I own one of these LED, it is very very bright. It is very very cheap also (0.6 RMB) or about USD0.10

It work in 3.6-3.8 v

They claim the brightness is (mcd):20000-40000

Which do not known how to calculate. I can do a test for you if you tell me how.

[kentsin]

Dear Daniel,

This one very similar to the one you show in the photos, they claim


http://item.taobao.com/auction/item_det ... 4f2e05.htm

6.5-7.2V 700mA
200~240lm
2700-3300K

How many of these should I got for two cameras?

Or I get more leds, with a 130-150lm each?

Will more leds shine the pages better?