Lights for Archivists?

[StevePoling]

i read on another thread that some archivists won't allow allow artificial lighting when photographing old stuff. And whatever natural light comes in through the window is UV filtered. This got me wondering about the spectra of various lighting options to learn which is better, in the sense of being more likely to get the OK from a strict archivist.

If memory serves, a fluorescent bulb generates plasma that emits UV light that hits the phosphor of the lamp which in turn fluoresces in the visible band. Presumably, some of that UV coming off the plasma makes it past the phosphor and glass. I figure that UV must make archivists growl.

And incandescent lights can get hot, and though they may be better UV-wise, they're probably disliked for the heat they radiate onto the illuminated material.

This leaves us with LEDs. Being solid-state devices, I figure they want to radiate in a very narrow band of frequencies tied to band gaps and magic quantum stuff. Despite this, Dan reports good results from LEDs in his 3rd generation scanner. I wonder if you could sweet-talk an archivist into allowing LEDs.

On the other hand, many sensors are IR-sensitive if you remove filters over their lenses. And I recall that LEDs can happily emit IR invisibly. Which leads me to wonder whether you could bring in an infrared LED flash and infrared sensitive digital camera, and use that combination to image archival materials. If such is a safe and reasonable approach, then I'd suggest an LED array consisting of a mix of IR and visible light LEDs. Then you can make a big show of turning off the visible light LEDs without disclosing that the IR LEDs are still flashing.

And since LEDs consume relatively little juice, you could probably run them off a battery pack that charges a capacitor. Keeping your system off the electrical mains must lift archivists comfort level, too.

I'm just speculating here guys. An interested amateur with a little bit of knowledge. Smack me down if this is hurting the site's signal-to-noise.

[Misty]

Speaking as an archivist here, I think I can help out. There's a good explanation of the issues in this chapter of the Canadian Council of Archives's free Red Book, a basic conservation guide. (Check page 19.)

Archivists don't like UV because it is the component of light that most contributes to aging paper - making it brittle and faded, like you're probably familiar with from sunworn posters and the like. LEDs are definitely good for both UV and heat, and while it seems to be hard to get a good lighting system together using them it's definitely possible. While fluorescents are typically UV emitters, their heat issues are significantly lower than incandescent and tungsten, and fluorescents are commonly available in no-UV versions. (There are also separate UV filters, though those can be costly.) No-UV fluorescents are commonly used for that reason - until LEDs really take off, they're the easiest solution. I think LED systems have the most promise though, personally.

As I've mentioned a few times before, halogens are one of the most problematic types both for heat, and because they're high UV. That's why I keep telling Dan not to recommend them.

[StevePoling]

You've seen this, I presume: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1263464077

I'm wondering if I could replace my dual halogen lighting solution with a LED array. I really like the idea of leaving the LEDs idling until you push the button and then blast a ton of current through the LEDs for just a moment when the camera's snap.

The flash of visible light would be annoying in a public venue. I'd be interested to learn whether you could image monochrome materials with IR LEDs that nobody would notice.

[daniel_reetz]

That's what I designed here, but mine is specific to book scanning. Using RGB LEDs will only make things harder. You need to use white light LEDs to get the correct lighting. I described the whole circuit/etc already.

[Misty]

Like I commented there, I like the look of your LED lighting system but don't have the electronics skills to pull it off (or know anyone who does). I'd plan to use it in mine if I had the chance!

Wayne Toborg used a similar flash system at the Hill Museum & Manuscript Library, which he described in this paper. Unfortunately, he doesn't say what kind of lights they used - the paper is short on detail. I expect that, if you were using a black cloth light shield, you could minimize the annoyance to other people from strobing.

[Afish]

Why not put a UV filter film on the platen and design the system such that no unfiltered light reaches the actual book? A simple test would determine if photo quality is significantly reduced. Temperature can surely be reduced with fans or air conditioning directed strategically. A fixed platen could have a fans blowing on top and air conditioning cooling below.

[daniel_reetz]

Acrylic and polycarbonate both block UV (polycarbonate a lot more than acrylic). It would be interesting to measure the UV level on both sides of the platen surface.

[IcantRead]

Glass also blocks UV rays. It blocks out about 90% of UVB. I'm not sure what UV (UVA or UVB) makes books pages degrade. The reason why a halogen light has a piece of glass between you and the bulb, is so it dose not give you skin cancer. If UVB is what causes degradation of paper, then halogen lamps are fine to use.

[spamsickle]

The industrial halogen lights I use come with a UV filter, which for all I know is just ordinary window glass with "UV Filter" stamped on it. I never worried about taking a book to the beach, and I'm sure not worried that a few seconds of light per page is going to ruin them, but then I'm not an archivist shooting rare books in the back room of a museum with a fidgety curator looking over my shoulder.

[Misty]

Spamsickle, the point isn't that a single short exposure will damage it but that there's a cumulative effect. I'm sure you've seen old faded, brittle paper before! Your curator is fidgety because they have to deal with an aggregate of people all of whom think to themselves, "Well, this one small bit of light/whatever won't hurt it any." But yes, it doesn't matter much if you're not shooting rare or valuable materials, as many people aren't - the reason I've been bringing these things up is because some people are, and it's important not only to consider protecting the documents, but to consider the requirements of the environments they'll be working in. Given that those items are the physical property of someone else, it's important to be able to adapt yourself to their rules.

Glass and acrylic do both block most UV light, but I'm not sure that the glass that comes in standard consumer-level halogen lights is enough to protect documents.

Edit: On UV filters, check page 20 of chapter 3 of the Red Book. They mention that window glass does filter out UV below 330nm, but not above that. There is separate UV film that can filter out light above 330nm, but that's not going to be built into your standard consumer-level halogens. UV film is pretty easily available though, if not dirt cheap.