According to this Chaos: Industry-leading design and visualization software a typical 100w bulb produces 1500 lumens.
When I input this the room is very very dark. I have to put in at least 150000 to get any decent light.
I’m working in mm, gamma 2.2 and my Vray camera settings are default. What is the correct calculation for this workflow?
Thanks
If I am working in mm should the system scale be 1 unit = 1mm or 1 unit = 1 metre?
I set my system units to be equal to 1 metre, modelled a typical bedroom which is 4.5m x 4.5m x 2.4m. Then added a camera with a typical setup of shutter speed 8 (1/8), f number 8 and ISO 125. My Vray render settings are maxed out, high dmc, light cache and IR. The Vray light is set to luminous power with an intensity of 2600 which is roughly a 100watt bulb. Gamma 2.2 setup.
And i get this… 
Its not what I expected at all. Why so bad?
Are you using a Vraycam? In real life one thing you can do is lower the shutterspeed of your camera. You can do this for your vraycam. You can also lower the f-number.
One bulb light does not create much lighting although you might think it does but the human eye has built-in shutterspeed 
that render is shutter speed 8 f number 8 and ISO 125 but its so dark and noisey. Also the lamp is very burnt out. If I increase the light any more it will be even worse
I have adjusted the camera settings so that the scene is much brighter now but as a result the lamp has gone super nova. I’m trying replicate a real world environment, but having little success. There doesnt seem to be much info on how to do it either.
Any advice on settings up a 4.5m x 4.5 room with a 100watt bulb? and getting it look right with linear colour mapping.
I always end up with a very blown out light source, no matter what camera exposure, obviously the brighter the image the more blown out. How exactly is this supposed to work?
Is there an example anywhere showing how to set up a real world light solution with a linear workflow and camera exposure?
Blown out light source is to be expected in real world too. Any single light bright enough to light a room of that size to the level you are is going to be burned out in a photo. Be careful that you are not referencing retouched or professionally shot images - where someone will have likely taken the time/pains to balance out the lighting artificially. My advice would be to take a room in your own place and light it with a single bulb and photograph it and see what the light source really looks like when the exposure it open enough to pick up the whole room.
There is a reason why photographers often use many lights to do interiors 
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But I’m following guidelines here. Vray says that a 100watt bulb is about 1500 lumens Chaos: Industry-leading design and visualization software. Im not referencing any photo, I’m referencing my own bedroom with my eyes
It just seems odd that there’s no example of real world lights being used with correct exposure etc. none that I have seen anyway.
You cant follow your own eyes - as was pointed out in this thread they do not react to light the way cameras do. Vray matches the physical behavior of cameras, not your eyes (although it is possible to get closer through tone mapping settings and gamma corrections etc)
That was what i was wondering. Is there a method to get close to the human eye, rather than a photo?
Here’s a thread which might be useful - http://www.chaosgroup.com/forums/vbulletin/showthread.php?28260-VRayLight-units&highlight=light+efficiency
I have read that before and it talks about settings within Vray lights that aren’t there any more like Normalize intensity. I wondered how that translates to the new version of Vray.
Also Vlado states this. http://www.chaosgroup.com/forums/vbulletin/showthread.php?38860-Vray-lights-in-newest-build&highlight=lumens+light+intesity
which goes against this from the thread you just gave me
So which is correct? Are lumens effected by system units or not?
Ah okay.
So Gijs post is taking into account Vlado’s explanation that vray uses watts per square metre to calculate it’s intensity so if you’re using a different display unit (lets say centimetres), you have to compensate for that with your multiplier values (multiply them bx 10 x 10) so that they become equivalent of metres squared again.
What vlado is saying above is that it doesn’t matter what system unit you use once the light is the correct size for the real world too, since vray light intensity is based on multiplier and surface area, you need to make sure that your light / bulb is the correct size for the same bulb in the real world. In your case of lumens, a 100w bulb is giving off about 1700 lumens, so if you are making a vray light you need to make it the same physical size as the equivalent bulb in the real world too, so a bulb with a radius of 5cm in the real world must be either 5cm or 50mm or 0.05 metres.
It also seems that when giving out lumen ratings, the bulb manufacturer are taking into account how physically big the source is too - so the lumen value for the bulb is for a bulb of a very specific size so once you also model a bulb of that specific size, you should get a similar output as it’s real world equivalent. I’ll do a test one of the evenings with an slr in a room in my house to see if it’s in the right ballpark.
so if I’m working in metres 1700 lumens for a 5cm radius bulb is correct. If I am working in millimetres I need to do what with that 1700? times it by 1000 x 1000? that would be 1700000000???
where did that 0.026 come from?
I’m so confused 
Do I need to adjust the lumens depending on system unit setup? Or is 1700 lumens correct if my bulb is 5cm or 50mm? I work in mm and everything is to scale. But my results are so dark.
Yeah It’s horrible!
I think all of those nasty multipliers were based around the fact that people were previously using watts which is per square metre so they had to figure out how big their light was and adjust their multiplier accordingly. Lumens seem to be a much kinder value to use since it is actually taking into account the size of the light already. So for example if a manufacturer says their 100w bulb is 1700 lumens, they’re saying they measured a 5cm radius 100w bulb and it gave off 1700 lumens of light. If they had a 2.5 cm bulb, it’d have a quarter of the surface area so it’d probably be something like 1700 / 4 lumens - the quoted lumen value is for a specific wattage bulb of a specific size. So in this case, no you don’t need to adjust the lumen value, and it also seems that lumens is a total light emitted value, regardless of the size of the light so for the correct shadow size, you’d just have to make your bulb the same size as the light.
I’ll try and shoot a few shots at home this evening to see what kind of iso / shutter I get in a room only lit by the ceiling lights!
Thanks for clearing that up There really should be an updated sticky post on this Basically what Vlado posted back in 2005 is now obsolete because Vray lights use lumens now and not watts therefore it doesn’t matter what units of measure you use to set up the scene. As long as its the correct scale 1700 lumens is 1700 lumens, no calculation is needed.
I hope that’s right
Exactly - I’d say if you use default multiplier units then it’s watts per square metre and all that horrible multiplication. Lumens seem to be an absolute value of light emitted, regardless of the surface area / radius of the light - I did a quick render test of an area light set with lumens and then doubled it’s size and it had no effect on the amount of light in the scene - having the right light size is purely for shadow accuracy but 1700 lumens is a total amount, unlike watts which are measured by surface area and thus affected by light size.