Timer for home made UV light source ideas?

I'm gathering parts to build my UV light box. What do you recommend for controlling the exposure time?
I could probably do it manually with a stop watch and a light switch, but it might be nice to have something a bit more sophisticated.

I imagine a Gralab 300 would do fine. But before I go and buy one of those I wonder what other people are using.

I'll be using it mostly for Cyanotypes but of course I don't yet know what approx length of exposure times I will be using.

Thanks,
Keith

Are you using LEDs or fluorescent tubes in your source?

If you are using LEDs, a GraLab timer will work just fine. This is what I use these days.

If you are using fluorescent bulbs, I would skip the timer and just leave the exposure unit on for the duration of you session. Supposedly, fluorescent bulbs have a warm up period in order to get stable output... that is the lore anyway, I never confirmed this myself. Thus, it was thought that you got more consistent results by leaving the unit on between exposures. Before I converted my unit to LEDs, I used a GraLab timer that had a buzzer to indicate when the set interval was finished to time my exposures but not to control the exposure unit.

I've been using a GraLab 505 digital timer for my home made box, I use 6 fluorescent tubes. I'm switching to a GraLab 300 for it though (for no other reason than I have one I want to use).

keithostertag said:

I'm gathering parts to build my UV light box. What do you recommend for controlling the exposure time?
I could probably do it manually with a stop watch and a light switch, but it might be nice to have something a bit more sophisticated.

I imagine a Gralab 300 would do fine. But before I go and buy one of those I wonder what other people are using.

I'll be using it mostly for Cyanotypes but of course I don't yet know what approx length of exposure times I will be using.

Click to expand...

I've never used one of these LightMeasure devices, but they measure the accumulated UV exposure rather than use time so can account for light source drift or cloudy skies if exposing outdoors. The fancy one can shut the light source off automatically (well...not the Sun, obviously!) when a predetermined amount of exposure has been reached:

http://www.lightmeasure.com

fgorga said:

Supposedly, fluorescent bulbs have a warm up period in order to get stable output... that is the lore anyway

Click to expand...

To an extent, yes, but what you say is not necessarily true for all tubes. Tubes come in two types: the old-fashioned type that does indeed need a minute or so to warm up and reach their stable, high output level. They are also not supposed to be cycled quickly; they need to cool down before restarting them, otherwise their service life will be shortened drastically. Then there are the modern type that warm up quickly (in a few seconds) and can be cycled quickly as well.
Only the modern tubes should be used in UV exposure systems for obvious reasons of lifetime and repeatability of exposures. They should be used with electronic ballasts as specified by the manufacturer. The old, slow-start tubes have no place in an alt. process darkroom and should be discarded.

keithostertag said:

What do you recommend for controlling the exposure time?

Click to expand...

The easiest solution is to get a timer relay circuit from e.g. eBay or AliExpress etc. They're little PCB's with a few buttons, a small display (usually 7-segment leds) and a relay. They generally have several modes you can program them in; I use mine in a countdown mode, simply setting the number of seconds I want the light to be on and then running the unit. There are probably dozens of variants of this kind of device, and they're generally very cheap (a few bucks). Easy to implement in your own product. No need for dedicated darkroom equipment that's expensive, hard to get etc.