Let's talk about Lighting

[railman]

Dan

I think you would like this.
.
http://www.chestersgarage.com/documenta ... led-shield
http://www.chestersgarage.com/store/ard ... hield-kit/

This would make it easy to controll your leds from an arduino.

[daniel_reetz]

That's pretty rad! Of course you could connect the Arduino directly to the BuckPuck, but that shield does most of the work for you... thanks!

[reggilbert]

dear all,

earlier in this thread (top of page 3) i posted some research I did on cree leds, tentatively concluding that the Cree XP-G R5s are brighter for less money per lumen than the Cree XP-E Q5s that seem to be the current favorite on the forum.

i hope to start a scanner build soon and wondered if anyone had any comment on the ideal led to buy for scanning. i'm new to electronics of any kind and to leds in particular, so it would be easy for me to have failed to notice some crucial characteristic of the XP-G R5 that makes it inappropriate or no better than the Q5 for book scanning.

my aim is great brightness, as it seems to me that nearly all the scans posted on this site are on the dark side, compared to the scans I get from my flatbed. I expect darker scans make some difference in ultimate OCR effectiveness. many of the books I plan to scan will have substantial footnotes, which can be printed in as little as 8 point type and have a greater per-word likelihood of harder-to-recognize italic font. some authors put a lot of information in those footnotes beyond the bibliographic, so good OCR of that material can be as important as recognition of the main text.

i guess with what i understand to be the flexibility of the buck puck device, great brightness can be easily achieved by just having more leds, but i'd think each one should nonetheless be as bright as possible, at least if that is cost-effective

the post i wrote on this issue on page 3 of this thread is quite a bit to slog through, but if anyone feels like offering some guidance on this buying decision, I'd appreciate it

thanks in advance and happy holidays

reg gilbert

[Ryan_phx]

Okay, I'm about ready to pull the trigger on a BuckPuck and some Crees, but I have two questions before I do.

First, is the Cree XR-E Q5 still the favorite? There are a lot of similar LEDs from Cree on the Dealextreme site, and since I know nothing about these things, could someone tell me if the Q5 is still the best choice, or if I should go with another model instead?

Second, I don't need to worry about a heatsink or anything with these, right? I should be able to just mount the LEDs and the Buckpuck to a strip of metal or wood, right?

One other question: I have an old laptop power supply that outputs 18.5V, 4.9A, 90W. The Cree Q5 needs 3.7V, so I should be able to run 5 of them off this power supply, right? Or am I misunderstanding something fundamental here?

[vizzinni]

I wonder if this would work? Groovy Game Gear NovaMatrix LINX

It's priced at $18 and is modular, allowing additional links to be added for about $2.75 each. It's designed to run on 12v from a PC power supply. There's no other specs included.

This might be a decent option for those of us that are uncomfortable with a soldering iron.

[daniel_reetz]

Okay, I'm about ready to pull the trigger on a BuckPuck and some Crees, but I have two questions before I do.

First, is the Cree XR-E Q5 still the favorite? There are a lot of similar LEDs from Cree on the Dealextreme site, and since I know nothing about these things, could someone tell me if the Q5 is still the best choice, or if I should go with another model instead?

That's what I'm using, and I think they work well.

Second, I don't need to worry about a heatsink or anything with these, right? I should be able to just mount the LEDs and the Buckpuck to a strip of metal or wood, right?

The buckpuck doesn't need one, but the LEDs will need to be mounted, at a bare minimum, to a stick of aluminum. Get the 700mA puck if you don't want to worry much about heat - the 1000mA unit does get hot.

One other question: I have an old laptop power supply that outputs 18.5V, 4.9A, 90W. The Cree Q5 needs 3.7V, so I should be able to run 5 of them off this power supply, right? Or am I misunderstanding something fundamental here?

Sounds right to me. With the BuckPuck you should be fine. Better to work in even numbers though - I think 4 will be plenty for your setup.

[daniel_reetz]

I wonder if this would work? Groovy Game Gear NovaMatrix LINX

It's priced at $18 and is modular, allowing additional links to be added for about $2.75 each. It's designed to run on 12v from a PC power supply. There's no other specs included.

This might be a decent option for those of us that are uncomfortable with a soldering iron.

Vizzini, the only problem I can anticipate would be that the output is not as high as they say or that the color rendition might not be very good. I've been looking for a cheapish product like this one, but with a normal screw-base:

http://www.dealextreme.com/details.dx/sku.3325

Also, I ordered a set of these on eBay a month ago, they should arrive any day. Complete, turn-key solution:

http://cgi.ebay.com/White-10W-High-Powe ... 3cb3f3c0f1

[reggilbert]

What about these Cree R5s? A DX commenter says they put out a maximum 440 lumens at 1.4 amps, vs. what I understand to be the maximum 228 lumens at 1.0 amps for the Q5s Daniel seems to be using (judging from photos earlier in this thread), at a cost of only a $1.65 more apiece.

Would that mean that just 2 R5s would generate almost the same output (880 lumens) as 4 Q5s (912 lumens)? - for some apparent savings both in initial purchase and long-term energy use (unless you use Daniel's flash method, then only in purrchase).

I have only the barest grasp of electronics, so maybe that is calculating things all wrong, and I could easily be missing something else significant. For one thing, the two LED boards as pictured on DX are different, with four solder points for the Q5s and two for the R5s (I think this permits more potential control of the Q5s). Perhaps their Kelvin are different too - if I am looking at the right Q5s ("WG" type) and correctly reading the Cree XR-E and XR-C binning and labeling guide (PDF), Q5s are between 5700K and 6350K (page 7 in the PDF), while the R5s linked to above, according to the DX product page, are 6500K-7000K, whatever all that means - perhaps nothing, as presumably any Kelvin temperature can be accommodated in camera settings.

For the technically knowledgeable, more on the class of LEDs of which the Q5 is a member (XR-E) here, and on the class of LEDs of which the R5 is a member (XP-G) here.

Again, I have the barest grasp of electronics, so no reader should rely on the above comparison as definitive information, and anyone on the forum, please correct my inferences. I'd love to know for sure, as I am putting together a lighting fixture for my scanner as soon as Daniel posts his explanation for how to use the Buck Puck and will have to default to the Q5s, since I know they work, absent some confirmation from a knowledgeable source that the R5s are also likely to work.

[daniel_reetz]

There are some interesting, assembled options on this page:

http://www.goldengadgets.com/led-lights ... ights.html

If I had the ability to return all these lights I'd just buy every last one and test them out. As it is, I've spent over $400 on different lighting solutions in the last three months (some of which haven't arrived yet due to the Chinese New Year) and I'm uncomfortable with/a bit tired of being relied on as the sole source of information on this. I have presented solutions and specific recommendations about LED lighting since July 2009, but have seen only two or three people adopt them. This tells me that they are too difficult (which I understand -- some of the time) and also that lighting is not well understood. It also tells me that for whatever reason, lighting, particularly LED lighting, is a big source of hand-wringing for many builders. With that in mind, I am hoping we can get some people to try/buy lighting solutions like the ones above, so that we can identify something pre-assembled and angst-free.

These lights: http://cgi.ebay.com/Warm-White-10W-High ... 3a61a6081b were used by a forum member here in the past, and I have a set on order. I don't think everyone here can afford $70 for a pair of them, but they probably represent something close to the ideal.

As to some of your questions, reggilbert, LEDs have only two contacts. The 4 contacts on the star of the Q5 from DealExtreme are V+,V+, and V-,V- -- in other words, there are actually only two. The number of lumens from any LED is dependent on the current and driving voltage, as well as any variation within normal tolerances. The number of lumens claimed is distinct from the usefulness of the light. We want two things from an LED: high enough luminance to get a fast shutter speed (which, as I've said before, it has only a passing connection to the manufacturers claimed output) and high CRI - color rendering index, which specifies how well the lighting helps the camera/our eyes see color. Most 5mm LEDs, cool white LEDs, and very cheap LEDs have poor CRI, though they may be bright. I don't know offhand what advantages and/or disadvantages of the newer R4s might be. I'm not highly motivated to test with them as I still have Q5s laying around and have had proven good results with them. If anyone else feels adventurous, it would be good to hear someone else make some tests, spend some money, and show some results. Otherwise, Q5s are a safe bet for now.

EDIT-CONFUSION-BUSTER: Warmer color temperatures typically have better CRI. This is a little confusing because color is spec'd in degrees Kelvin for a blackbody radiator. 6700K is very hot temperature-wise, but the output light is blue-white color. 2700K, though cooler in degrees Kelvin, appears to us as red-tinged white, or "warm white". We want neutral or warm white LEDs for better CRI. See this discussion about CFLs for more info. http://www.treehugger.com/files/2009/09 ... r-cfls.php

[Ryan_phx]

Well, I ordered four Cree Q5s and a BuckPuck. I'm looking forward to seeing how well these LEDs work. I'm thinking of installing a switch on the back stand so that the downward motion of the platen turns them on, and the upward motion turns them off. It'll help keep the heat issue at a minimum.