The search goes on – for the perfect UV exposure unit. I’m not sure I’ve found it yet but I did actually spend money on something that I felt could come close; An LED flood light. What caught my eye was the wavelength in the UV-A range 385-405 nm. That is pretty close to the optimum wavelength for alternative processes, so I decided to give it a try.
My original plan was to construct an array of F20T8-BL fluorescent lamps. I picked up some fixtures that were on sale at the local building supply store. They were cheap enough, but the lamps cost so much I had to shelve the project until prices fell to a point I could afford them – yeah right. Needless to say that hasn’t happened and probably never will due to the dying demand for fluorescent lighting.
LEDs Are the Future
On the other hand I finally see production of LEDs strengthening across the board to the point that even the less common UV kind are coming down in price. This unit, purchased from Amazon cost under $30. It is small, light weight, consumes very little power and generates even less heat than a single 20 W fluorescent lamp and ballast. And much, much less than a 100 W metal halide lamp and ballast.
The unit I received is rated at 20 W and is constructed fairly well (except for the paint job). It includes a grounded AC cord and steel mounting bracket and has a good size heat sink which didn’t get too hot even after leaving the unit on for over an hour.
I attached the unit to my Minolta color enlarger so that the LED emitter was about 9.5 inches above my print and pointing straight down. This is the distance I visually judged would cover my entire 9×12 printing frame. I plugged it into a old style Graylab timer and picked out a 4×5 inch film negative set on top of a small sheet of pre-coated SunPrints cyanotype paper. I locked the frame and started with a 5 minute exposure, then worked my way up until the highlights were clearly over exposed at 20 minutes. I washed each print in room temperature tap water for 20 minutes, followed by a quick dip in dilute peroxide bath, then washed again and allowed to dry over night.
For comparison, I made a 5 minute exposure in late afternoon direct sunlight.
Row 1 top L to R – 5 minutes sun, 5 minutes UV lamp, 10 minutes UV lamp
Row 2 bottom L to R – 15 minutes UV lamp, 20 minutes UV lamp, 25 minutes UV lamp
Pros – Easy to use, cost effective, good results in limited testing. Small (~1 inch square) emitter is compact light source. This may result in sharper prints than a light source that’s spread out over a larger area.
Cons – I noticed an odd problem when I used my Graylab 545 digital timer. The lamp periodically blinked off then back on. This only happened with the digital timer and could be a problem with the timer, not the lamp. However, it doesn’t happen with either of my incandescent enlargers. Also, I got a unit with a bad paint job, maybe you’ll have better luck.
Next step up is HouLight’s 50 W unit which could reduce exposure time or increase coverage area. Of course it costs more than the 20 W unit but still a bargain compared to commercial exposure units.