diff --git a/electronics/bom.md b/electronics/bom.md
index 0c51374..daea809 100644
--- a/electronics/bom.md
+++ b/electronics/bom.md
@@ -20,6 +20,13 @@ Many people use a laser printer, but the ones I had did not deposit enough toner
 
 The printer I use is a Canon PIXMA iP7250, which is not all that expensive. For any Canon use the official "PGI" range or cartridges, as these are pigment based. With these I do not need to double up on transparencies to get great results.
 
+## UV light source
+I started out with a UV nail polish dryer which was ok, but the timer function could only do 120 seconds. Instead I built a little UV exposure box using an array of 5mm UV LEDs, 12 x 12 spaced about 1 cm apart. These are controlled through a MOSFET by an ATMega328, hooked up to a 16x2 character LCD and a rotary encoder. The time can be set, as well as the intensity (using PWM). I may one day post the code, schematics and 3D printable enclosure.
+
+UV LED strips will probably make for an easier build, and you can replace the bare ATMega328 with an Arduino just as easily, but I liked the challenge. The LEDs have turned out to be very effective, reducing the exposure time significantly.
+
+Whatever you use make sure you have enough control over the light source so that you can experiment and get good repeatable results.
+
 # Consumables
 
 ## Transparencies