Exposure control

I am looking to build a uv led exposure unit.
I would like to measure the emitted energy to shut it off when correct exposure is reached.

Photo sensitivity is quoted in Joules per unit area normally.
Anyone tried something similar please.

My main problem is finding a way of calibrating it.

Depending on the accuracy of the calibration you need, would calculating it be ok?
Datasheets most likely contain the information on the intensity of the light sources you use.

Previously i have used an arc light at 1 m and a normal tube based uv exposure box.

In both cases the variable warm up time of the lamps throws off the simple timing method.

Experimends with leds are showing hotspots where they focus.

The two marerials that give me the problems are solder resist and dry transfer film which have critical exposures.

Etch resist , pos or neg is generally forgiving.

So you need a diffuser for your LEDs and a more controlled process for the arc lamp (introduce a warm up period prior to exposure).

Shpaget:
So you need a diffuser for your LEDs and a more controlled process for the arc lamp (introduce a warm up period prior to exposure).

Diffuser, yes im hoping that doing that witha simple timer will solve the problem but its not looking hopeful at the moment.

Arc lamp, only way to have warm up period would be to use a shutter, commercial gear does that but its too big and messy for my uses.

Sunbathers can buy a cheap device that does this so it cannot be too difficult to implement i would think.