Artificial light intensity vs natural light

[alexnode]

My job is to do renders before construction for client approval in very short deadlines. Museums, expos, pavilions, planetariums etc Most of the times I just try to make it look good, but there are hundreds of times that we need to find an approximate lighting scheme that works to feed in the the work of the real life light designers. When they suggest to us a specific light fitting I would love to test it easily in Lumens or something like that. I usually work with a vray sun, hdri, vray lights plus loads of lightboxes, LED strips video projections, frosted glass etc. Things can go out of hand really early on, I would love to have an easy way to unify all these. For our practice we don't need 100% photoreal behaviour but an easy way to test real life lights would be really helpful. I am not even sure what a realistic value for the sun and the HDRI are. I usually have the sun at 1 the HDRI multiplied by 100 ? and then my lights start from 60 to 120. The same goes if i use sun 1 and vray sky 1. Which is obviously not right because a 60 multiplier is 37000 lumens almost a football stadium light.
I have been of the camp 'make it look right' but some times i need more than that.

[super gnu]

i think the default values for sun and sky are based on physically correct values. hence the "physical" tag. in theory if you use those, the physical camera, ies lights with correct values, set vray to not do any fancy colour correction, and get your *materials* physically correct, the result shoulnt be wide of the "physically correct" mark.

[fraggle]

OK, I'm happy to see that I'm not facing alone this nightmare. Seems that there is no physical accurate process at the moment.
This thread was not about physical accurate lighting vs non accurate tweak lighting. It was about trying to find out if there is a way to match as much as possible the real word to gain time. I know what means 60w spot, I have now idea what means 6000w or 60000w, or even worst lumens (thanks to Alexnode, now we know what mean 37000 lumens).
It will be great to get somebody from Chaos to give a feedback on this subject.

[mattclayton]

The balance between internal and external lighting has always been something i've tried to find a solution/workflow for. I definitely try and go down the physically accurate route setting up the internal lights to realistic (or close to realistic) values. But before i worry about that i setup my camera to settings i would expect to use as a starting point in a real world scenario. Those of you that have heard of the sunny16 rule will know that there are fairly specific guides to a range of lighting scenarios. (See attached a chart that i knocked up for the studio).

These are obviously guides, not law, but they're a good starting point! I start off with these settings, so for an internal something like F2.8, shutter speed 1/125 and ISO 100. Since the level of light you get from your HDRI can differ entirely depending on who has shot it and what number of stops have been used to capture it, therefore there is never a truly accurate value to set it at as per the values of the vray lights. Therefore i boost the render output value of the HDRI (leaving the vray dome light on 1.0) until i a level of light in the scene i'm happy with. I'll then turn on my internal lights individually or in groups depending on how i want to go about lighting the room. 9 times out of 10 they'll only need minor tweaks if any.

Hope that helps, works for me anyway!

[alexnode]

Thank you Matt this table looks great i already put it on the wall !
In the previous century : ) is used to buy 400 iso to 1600 iso film for interiors depending on the lighting conditions ... There was no way that you could capture a dark interior in a 200 iso film. Never used flash in my entire life!
I have to say that I still find all these settings a bit of an anachronism in DSLRs and in Vray. You don't have silver crystals in film because there is no film.
You shoot 'gigapixels' you touch your point you focus and from time to time you adjust the exposure if the setting is unusual or you want to darken it or to burn the shot. Rule of thumb for me is to do that in post-processing and capture as much information as possible.
From my point of view there is only exposure and geography. The ideal workflow for my type of work would have been to have an exposure 1 is something like midday, summer 30th parallel north and south. So you set up time - day - place - atmosphere you define north in your drawing. Automatically you have a suggested exposure. Mental ray tried that and it wasn't that bad. The feature that would make my life much easier though would have been to have light materials, multi- sub object self illuminated materials and vray lights to behave the same way. All being displayed in the light lister with three quality presets. When i usually break my scene is with self illuminating materials. Small peculiar led strips, led walls with frosted effect, video projections, colour printed lightboxes . Things change so quickly as we design that spending time turning multi-subobject material meshes to lights becomes a no go. So i usually fiddle with it until it looks right and after a while I start using all sort of values that have nothing to do with reality. In the middle of this mess a light designer comes in and starts throwing light fittings in lumens ...

[fraggle]

that may be an answer regarding vraylightmatl (instead of selfillu):
http://forums.chaosgroup.com/showthr...f-object/page3

Thank you Matt this table looks great i already put it on the wall !
In the previous century : ) is used to buy 400 iso to 1600 iso film for interiors depending on the lighting conditions ... There was no way that you could capture a dark interior in a 200 iso film. Never used flash in my entire life!
I have to say that I still find all these settings a bit of an anachronism in DSLRs and in Vray. You don't have silver crystals in film because there is no film.
You shoot 'gigapixels' you touch your point you focus and from time to time you adjust the exposure if the setting is unusual or you want to darken it or to burn the shot. Rule of thumb for me is to do that in post-processing and capture as much information as possible.
From my point of view there is only exposure and geography. The ideal workflow for my type of work would have been to have an exposure 1 is something like midday, summer 30th parallel north and south. So you set up time - day - place - atmosphere you define north in your drawing. Automatically you have a suggested exposure. Mental ray tried that and it wasn't that bad. The feature that would make my life much easier though would have been to have light materials, multi- sub object self illuminated materials and vray lights to behave the same way. All being displayed in the light lister with three quality presets. When i usually break my scene is with self illuminating materials. Small peculiar led strips, led walls with frosted effect, video projections, colour printed lightboxes . Things change so quickly as we design that spending time turning multi-subobject material meshes to lights becomes a no go. So i usually fiddle with it until it looks right and after a while I start using all sort of values that have nothing to do with reality. In the middle of this mess a light designer comes in and starts throwing light fittings in lumens ...