Sun intensity in U4?

gnoop

Isn't it important for proper PBR  to have physically accurate sun intensity ? So why in game templates I see like 2,5 lux,  some you tube tutorials suggest  15 lux ,  in  Archiviz template  I see 5000 lux  while  as far as I know it's  120000 lux for direct sun in reality ?

What should I use  for a typical modern HDR style  outdoor game scene in Unreal?      And what auto -exposure settings?      We use 120000lux in our own  engine.      Why in Unreal it seems irrelevant?

in Blender both Cyicles and Evee   works better with phisically accurate intensity of sun and sky light  for example  if you  are doing dynamic day/night cycle .    Better shadow/light contrast,  better looking Filmic  output view transform with proper exposure adjustment. 

So how should I approach to this in Unreal ?

leleuxart

It seems irrelevant because it's not entirely necessary to achieve photorealistic results. As long as the direct to indirect lighting ratio is similar between the two methods, it doesn't matter what the intensities are. Physical light units really only help with consistency and speed.

UE4 doesn't default to using those units to not break existing content and to not force anything on the users. It just adds an additional level of complexity when a good chunk of the userbase doesn't care or need it.

The sunlight isn't actually 120,000 Lux. Unless specified for specific conditions, an illuminance reading includes all lighting hitting the sensor which means 120,000 is sunlight and the skylight(plus any other occlusion and bounce light).

To properly expose the image, you can use the spot/incident meter in the Eye Adaptation viewmode to get the nominally correct EV. Measure the illuminance on a flat white surface, which is generally perpendicular to the sunlight or placed horizontally in the scene in the area you want to expose for. Make sure the surface is fully rough, pure white, and with no normals, otherwise the luminance to illuminance conversion will result in an incorrect value. As of 4.26 UE4 will provide the EV weighted for 18% gray(spot meter) but you can grab my modified shaders for 4.24-4.26 that include the nominally correct EV based on illuminance(incident meter). My shader for 4.26 includes both. https://github.com/bleleux/CustomUE4/tree/master/Shaders/

gnoop

Thanks leleuxart   .   Yeah ,  I see your point  about 120000lux .     In fact  the Archiviz  template  with dynamic sun/sky looks kind of ok  with 5000 lux  with proper exposure adaptation  when you move from indoor to outdoor  except the very same  issue we have in our game:     Once the sun goes down but not  beneath the horizon yet  the sky  is getting too over exposed   and in general having  a bit overexposed haze  90 deg aside from the sun .       Well, contrary to what I usually see with my own eyes.

So I wonder if Archiviz  template is somehow too complex for a game lighting  and what should I set up for typical  day/night cycle  in a  modern game  supporting HDR monitors.    

In our game we have super blinding sun at  such monitors btw  . It's posteffect but still connected to proper physic values as I know . 

Or all of those  is totally irrelevant and could be anything suited to an artist taste.   Wonder what people really use in modern projects?