I’ve put together a simple, no-frills guide to building an inexpensive 365nm LED exposure unit, based on a design I use in my own darkroom. You can download it free here.

The guide walks through the complete build, including the design decisions behind it and the practical trade-offs involved. It’s based on units I’ve built for myself and for others, and focuses on a straightforward, reliable approach using readily available components rather than specialist parts or kits.

The design is built around a few clear goals:

• Lower cost than commercial units and kits
• Built from readily available components
• Based on proven design principles and component choices
• Easily customisable to suit your needs
• Lightweight and portable
• Optimised for 365nm UV output
• Capable of exposing up to A3+
• Short, consistent exposure times
• Compatible with an external darkroom timer

In practice, I was able to build a unit using 60 LEDs per metre for around £250, and a higher-output version using 120 LEDs per metre for around £350. The design is flexible, so you can adjust it to suit your own budget, working methods, and available space.

I use my unit primarily for photopolymer etching (photogravure), but it will work equally well for a wide range of alternative photographic processes that require controlled UV exposure such as platinum/palladium and cyanotype.