Hey guys,
I was really looking forward to this and today I finally gave it a first shot and man…I have to say its again just half finished and a lot of stuff feels weird IMO.
Regarding the difference between 4.19 and earlier versions in regards to lumens etc…I dunno what the deal is there but it definitely feels weird and off. However, if I tweak the exposure to something that makes sense to me, the new lumen values work perfectly! I don’t know though why you would want candela as default. I never use that and usually, light manufacturers specify their bulbs and spots in lumens …sooo…¯_(ツ)_/¯
The thing that really puts me off though is that a) directional lights still don’t use lux or something that makes sense in regards to measured exposures like FStops and b) the manual camera and autoexposure work completely different still!
autoexposure now has 20 stops of range, which works perfectly with the new lumens. If you lock autoexposure at min/max EV 8 and make a 1000 lumen spot in a dark room, that looks very accurate. Now bump up max EV to 16 and tweak the sun intensity to match…same with sky brightness. Then you have something nice that follows the sunny 16 rule and still makes sense in regards to dynamic range.
Problem though, those settings don’t match at all when using manual exposure which…well…sucks.
Hopefully someone with more knowledge could shed some light on this…preferably from Epic 
If anyone is interested, I am going to work with the new exposure system in the next lighting academy, coming next week. So I am really looking forward to explore this more
Cheer!
Daedalus