HouLite UV Exposure Light – UPDATE

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.

Breaking News – UPDATE

I liked the 20W unit so much, I upgraded to the 50W version! Sorry, I just had to say that. More on that later.

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.

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Test Setup

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.

The Results

Photograph – Council Overhang, Starved Rock State Park, near Ottawa, Illinois by the author

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

Bottom Line

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 50W unit which could does reduce exposure time by about 50% – yeah! – and increases coverage area too. Of course it costs more than the 20 W unit but still a bargain compared to commercial exposure units.

More Power

As Tim the toolman says more power is more better. It’s true. I’ve been printing with the 50W unit now for a couple of weeks. It’s not surprising that the results are right in line with expectataions. Especially nice for my classic cyanotypes which took up to an hour with the 20W unit, the new lamp is producing nice prints in half that time.


  1. Brandon says:

    This looks like an easy and low cost alternative to one of the large lighting units. Have you had a chance to try the 50 W unit? If so, what are your thoughts? Thanks.

    • admin says:

      I’ve given the 20W unit a good workout but haven’t tried the 50W yet. I’ve found that the 20W will produce a good Gum Bichromate (potassium dichromate) exposure in about 25 minutes at a distance of 18 inches. It seems that the classic cyanotype formula is less sensitive and needs about 60 minutes at 12 inches. I would like to get the higher power unit. I believe it would shorten exposure times.

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