Building an LED exposure box for cyanotypes and other processes

A practical guide to building a safe, reliable LED exposure box for cyanotype printing, enabling consistent results without relying on sunlight.

Writer and photography / Manfred J. Semmler

To be able to produce cyanotypes at any time, even without sunlight, I built an exposure box. The simplest solution is to take a piece of cardboard with a base slightly larger than the paper size, remove the bottom completely, and cut a rectangular opening in the top. You then place an LED spotlight on top for exposure, and the setup is ready.

“I wanted something more convenient: a permanently installed box that would not require placing the entire box over the paper for each exposure.”

Materials to build a UV exposure box

First, I compiled a materials list for the 42 × 30 cm (DIN A3) paper format.

For the exposure stand:

• Wooden board measuring 55 × 50 cm
• Planed squared lumber, 5 × 5 cm wide and approximately 75 cm long
• 2 sufficiently long metal brackets with screws
• Shelf brackets for hanging, approximately 35 cm long
• Short rail for shelf brackets
• Angle profile or wooden strip, 30 cm long and approximately 2 cm wide

For the box:

• Cardboard, 50 cm high, with a base area significantly larger than 42 × 30 cm
• Sturdy aluminium foil
• Carpet tape
• Fabric tape

And finally:

• 50-watt 365 nm LED lamp, the one used is this one. The DIN A4
• 1.5 cm thick wooden board measuring 45 × 32 cm (as a flat surface for the paper and glass plate)

How to assemble the UV box

I first assembled the exposure stand. I chose a shelf bracket from which to hang the LED floodlight above the cardboard box. The housing of the LED floodlight can become hot, posing a fire hazard. To secure the floodlight to the narrow shelf support arm, I also mounted an equally long angle bracket to the arm. A suitable wooden strip would also work; I already had the angle bracket available. The LED floodlight is screwed in place so that it sits loosely over the opening of the box.

The box

I used a moving box that was stored in the attic. First, I cut off the bottom flaps, then cut a hole in the top slightly smaller than the surface area of the LED floodlight. I also removed about 6 cm of cardboard from the bottom of one long side of the box. This opening serves as the insertion slot for the support plate holding the paper and glass pane.

Next, I covered all interior surfaces with aluminium foil. The foil reflects the light and helps ensure even illumination. Finally, I sealed all edges with fabric tape. The box was then finished.

To make it easier to pull the carrier plate out of the box, I screwed in two eyelets and attached a ribbon.

An additional advantage of this box is that exposure times are no longer dependent on the UV intensity of sunlight. With this setup, the exposure time is a constant 6 minutes. It depends on the wattage of the LED floodlight and the distance between the light source and the paper, and must be determined individually if these parameters change.

Warning: I advise against using a conventional UV lamp with several hundred watts, as such lamps become very hot and therefore pose a fire hazard.

An exposure box can also be built for paper size 21 × 29.7 cm (DIN A4). In that case, a 30-watt LED floodlight suspended approximately 30 cm above the paper is sufficient. The dimensions of the exposure stand and the cardboard box must be adjusted accordingly.

If you still have a projection stand from your analogue days, it can also be modified for this purpose. I built an exposure box for DIN A4 paper from a projection stand and, in addition, the DIN A3 exposure box described above. Good luck!

The article is available in French and German too:

French: Construction d’une boîte d’exposition à LED
German: Bau einer LED-Belichtungsbox

Manfred J. Semmler photographs travel, street life, and concerts, using available light and shadow to shape mood. His work balances objective observation with a deeply personal, subjective perspective. See his gallery here.