Simple Hack to Measure Screen Brightness with Your DSLRs
I know it's a constant bone of contention that The Verge uses 65% display brightness in the battery life run-down tests, even though that figure will vary wildly depending on how brightly the screen comes from the factory. I know it's way too much to ask for you guys to invest in a $1000 photometer for display measurements, but since you guys already use nice DSLRs for your product photography, here's a simple hack that will let you accurately measure the display brightness using tools you already have!
1) Open a blank white screen in your photo editor.
2) Set your camera to manual focus, and focus to infinity.
3) Set ISO to 400, Aperture to f/5.6, in Aperture Priority mode.
4) Put your camera at close range (20-50 cm) so that the entire display is filled with white.
5) Read what the exposure time is. If it is 1/100s, the light reading is approximately 100 candela/m^2 (100 nits). 200 nits is a common standard measurement, so adjust the display brightness until your camera's exposure reads 1/200s.
6) If you are using a DSLR, make sure to take 2 pictures - one in portrait, and one in landscape orientation. Because LCD screens are polarized, and DSLR metering relies on polarization, you will get slightly different readings. The brighter (i.e. faster shutter speed) reading will be more accurate.
7) Done! You've now calibrated your screen to 200 nits in less than 1 minute! Feel free to sit back, content in the knowledge that your readership will no longer be able to complain, and that you've done a good job as an editorial team in promoting consistency and honest journalism.
Hope this helps!
(Credit: this procedure was cribbed from this excellent tutorial)