Vray light Lumens

[Guest]

According to this http://www.spot3d.com/vray/help/150SP1/light_params.htm 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

[Guest]

If I am working in mm should the system scale be 1 unit = 1mm or 1 unit = 1 metre?

[Guest]

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/, 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?

[nils_p]

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

[Guest]

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

[Guest]

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.

[Guest]

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?

[Guest]

Is there an example anywhere showing how to set up a real world light solution with a linear workflow and camera exposure?

[simmsimaging]

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

b

[Guest]

But I'm following guidelines here. Vray says that a 100watt bulb is about 1500 lumens http://www.spot3d.com/vray/help/150SP1/light_params.htm. 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.

[simmsimaging]

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)

[Guest]

That was what i was wondering. Is there a method to get close to the human eye, rather than a photo?

[joconnell]

Here's a thread which might be useful - http://www.chaosgroup.com/forums/vbu...ght+efficiency

[Guest]

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.

[Guest]

Also Vlado states this. http://www.chaosgroup.com/forums/vbu...light+intesity

It doesn't matter what units you use, but that your scene is correctly modeled to these units. For example, it doesn't matter if you use meters or centimeters or millimeters for your scene units, so long as in all cases your room is e.g. 6 by 4 meters or 600 by 400 centimeters, or 6000 by 4000 millimeters.

Best regards,
Vlado

which goes against this from the thread you just gave me

Well, it isn't all that difficult. Consider the following:

If you are working in mm, multiply by 1000 x 1000
If you are working in cm, multiply by 100 x 100
If you are working in dm, multiply by 10 x 10
If you are working in inches multiply by 1/(0.0254^2) (approx. 1550)

If your bulb emits e% light, multiply the resulting number again with e x 0.01

The size in units of your light does not matter when normalize is checked, you 'only' have to take care about the units.

So which is correct? Are lumens effected by system units or not?