If you starting reading about measuring light, you quickly run into a morass of different units. Lumens, lux, footcandles, candela, watts per meter and many more. Complicating this are things like steradians, and it gets confusing in a hurry.
Bottom line: You want to measure in units of lux, as that's the unit that matches the response of your eyes.
The tool required is usually called a photometer. Most of the ones you'll find for sale are for use by photographers, who also need to measure lux for similar reasons. However, none of the photo units are sensitive enough for watch use, as they're designed for situations that are usually pretty well lit. We need a scientific photometer, with low-noise CCD sensor and matching Schott filters. These are not cheap. Think thousands of dollars. (!!)
Hardware and software
(More on this as time permits, for now please follow the links)
- UDTI/Gamma Scientific flexOptometer with CCD sensor and matched filter set.
- ABS housing and UV LEDs
- Computer with
- Software: My open-source flexOptometer, hosted at the awesome GitHub
- See Design and make your own watch for lume sources and resources.