Here is a link to a spreadsheet I've developed to calculate projector brightness: goo.gl/Q6NDQz.
This is a google sheet, so in order to use it you'll need to make a copy in your google drive or download the spreadsheet in another format .
Please let me know if you find this useful and don't hesitate to give feedback so that I can improve it.
Note that this is shared under Creative Commons: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)
