-Added "measuring luminance" and "damage" sections - added to "general recommendations" - deleted sentence about carbon arc lamps having superior color quality, can go on a carbon arc page - added "lamp alignment steps" made that section a little easier to follow step by step - added a "see also" section --Rlyon (talk) 09:43, 17 February 2019 (PST)
Need to Check
" A lamp alignment should be performed when a new lamp is installed and periodically thereafter because the position may drift over time." - I think it actually only needs to be done a second time after a certain number of hours but after that the position does not drift. Must verify. --Rlyon (talk) 10:59, 17 February 2019 (PST)
I believe the amount of drift will depend on the installation. An auditorium with a steeper throw will drift more than one where the lamp is on an even plane. Based on our technician's recommendations we refocus our digital lamps every month. In a perfect world, lamps for film projectors should probably be refocused on a similar schedule.
Luminance
Added a discussion of fixed-height vs. variable-height masking, since it greatly affects the light requirements.