http://www.diybookscanner.org/forum/vie ... 110#p17661
I had ordered one of this 10W LED lights from Amazon:
http://www.amazon.com/Waterpoof-Outdoor ... roduct_top
It just arrived and of course I had to try it out, so don't take these preliminary results as anything more than a quick assessment evenness of the light distribution and a first attempt at colour. These were taken at night so there was no daylight.
First impressions, the light is very well built, much more compact than I expected, impossibly bright to look at directly (as you can get the idea from the reflections in the pictures below) and is a good general light but is probably not bright enough for most people to get the kind of results they'd want from good book scanning. My impressions are 2x20w will probably satisfy most people. That being said I'm happy with this lamp because keep in mind that my overall objectives are quite different from most who will be looking for more perfect results and have more elaborate scanners and cameras. My objectives for this lamp were:
a) Get more even lighting across the page than I was getting with ambient light or a clip lamp to the side so ScanTailor generates more evenly weighted text (otherwise it generates somewhat heavier letters in the less well lit parts of a page) as my primary objective is high quality OCR not archival or other purposes.
b) Eliminate the reflection of the camera, camera arm and other items in the image (as can be seen in the images below taken from before).
c) Given the limits of my rather simple camera (an Olympus VG-130 14MP http://www.olympusamerica.com/cpg_secti ... sp?id=1533 ) try and get a reasonable colour rendition if there is a white balance setting that understands this light.
d) Add a lamp to the scanner with virtually no handiwork.
Now over all, I really don't need the light because ScanTailor does a phenomenal job, but I would like to have a reasonably good original should I need it for some future purpose.
WRT my objectives:
a) A more even light is produced if it is tilted up, away from the platen and towards the camera rather than (as in the picture) pointed right at the platen. I'm happy very with the results compared to what I was getting before and the lighting is much more uniform than it used to be and probably as good as I'm going to get it with 1 $10 lamp and my other design constraints. My objective here has been met.
b) Clearly there is a problem with larger originals as the light is reflected in the image (and creates a secondary purple hot spot). But if the platen is moved 2.5" away from the main post then the problem is solved, so I will just cut a new pipe for the camera arm that's a little longer. Otherwise all other reflections are gone and my objective here has been met.
c) Colour is not half bad on the auto white balance setting of my camera. The brown paper wrapped over the book cover (you can just see the edge of it to the right of the page in the 3rd picture showing page 81 of the book) is very close to the actual colour. I'll try again in the morning, when there's daylight, and see if I can do better with the mixed light. Otherwise, I'm happy with what I'm getting compared to what I used to get (which was basically worthless colour). My objective here has been met.
d) Well, as shown, there was no handiwork

The pictures below are:
1) The temporary set up I've got showing where the light is placed (using the temporary bungee cord mounting). The light is about 14" away from the surface of the platen.
2) Result I used to get with a small original (standard book) before I got the lamp in daylight (but wrong white balance setting). Note the reflections
3) Result at night with a small original (standard book) using the lamp with the camera set to auto white balance setting. Colour is actually quite accurate, no reflections and fairly even lighting.
4) Result I used to get with a larger original (letter size) before I got the lamp in daylight. Note the reflections.
5) Result at night with a larger original (letter size) using the lamp with the camera set to auto white balance setting. Colour is actually quite accurate, lighting could be a little more even, and platen has to be moved 2.5" to remove light reflection.
6) Result at night with a larger original (letter size) with colour using the lamp with the camera set to auto white balance setting. Colour is actually quite accurate, lighting is not bad, and platen has to be moved 2.5" to remove light reflection.
7-10) Result at night with a larger original (letter size) with colour using the lamp with the camera set to various white balance settings: Cloudy, Fluorescent, Incandescent, Sun.
Well hope this helps people get an idea of what one 10W LED bulb does.
Overall I'm very happy with the performance. It's let me meet my objectives better keeping in mind my design constraints.