Taking a look at the stats under battery in settings mine currently lists Screen as 63%. I've lost 19 percent in an hour and 10 mins. So is correct to surmise that in that 70 mins my screen being on has been responsible for reducing my battery level by approximately 12% using the following
total % dropped x item % used = amount of total % item is responsible for
19% x .63 = 12%
I'm likely wrong but I sure hope that it's safe to calculate that way...