Light Multipliers with LC and Vray Camera

[prey1979]

Hello all,

I was wondering if this is normal, i have an interior etup with LC as teh secondary pass, using a vray camera and vray sun shooting in from the window in the scene. I have a few photometric lights and a few vray lights but what i find inorder for the Vray LIghts and the Photometric lights to even have any remote effect i have to crankt he multipliers up to insane levels. is this normal? When i have used non vray physical camera my multipleiers have been in the single digits.

Kind Regards

Ryan

[vlado]

You need to have your scene units set up properly when working with photometric lights and the physical camera. It does not matter what the units actually are, so long as your model is correct in relation to them.

Also, when using the physical camera, you must use correct exposure for interior scenes (e.g. something like ISO at 800, shutter speed about 100, f-stop maybe at around 4).

Best regards,
Vlado

[prey1979]

Thanks Vlado,

I have my units set to imperial its actually a scene i had started doing without LC as secondary, was using IR map for Primary and QMC as secondary with a standard camera and direct light. I wanted to try using the vray sun and vray camera as i loved the feel of the lighting, i managed to get the correct exposure using the sun lighting the scene through the window but any interior lights i put in have no effect i think it maybe because i brought the lights in from another file... but the vray lights i created where new and tehy have to be cranked up high for them to affect the scene

[MikeHampton]

Light Valdo mentioned.. for the lights to fall within an expected range.. the vray camera has to be set to expected values for what you are trying to accomplish.

I've seen scenes where people had used very strange light settings.. but then offset this by equally strange camera settings.. and vice versa. The end result may have looked fine... but only because two settings (lights and camera) were proportionally equally out of whack with each other. Other times, someone may have had a specific reason for doing this (making the shadow areas lighter, or whatever)

First off.. I find it easier to deal with just a few lights at a time rather than trying to light your entire scene at once. That makes it easier to see what each light is contributing to your scene. And any light that you can instance... do so! That makes it easier to adjust the lighting.

Personally in the global switches, I tell vray to use the 3Ds max photometric scale, because I have no idea what it's doing if you don't have this checked. Anyone?

So once your set your camera to what might be an expected (non flash) camera settings you can begin to place your lights.

For a vray light.. change your units to Lumens. For a max light.. just think of the intensity multiplier in lumens. Do a google search for lumen output vs. wattage and you should be able to easily find some charts to give you what the lumen output of various kinds and wattages of lights are.

For example: 1) A 100 watt incandescent light has a (maintained) output of 1435 lumens or an intial output of 1750 lumens. 2) A 40 watt T8 Flourescent bulb has a (maintained)output of 3353 lumens or an inital output of 3725 lumens. And so on. You can also find charts that show you the correct colors (indoor or outdoor white balance) that different types of lights should be.

These lumen values are what you want to use for the intensity value of the light. Additionally for Max lights.. you want to set the falloff to inverse square. This is how light behaves. Of course this is assuming you are trying to mimic real light fixtures and such. I find that however.. with the max lights.. you need to set the start value of the falloff to something other than zero. Depending upon how far away the light may be from the first surface it would strike.. I usually set this value somewhere between 2" and 6". For a 20 foot plus tall ceiling.. it may be 5-6". For an 8-10 foot ceiling.. maybe only 2-3". Here is where you really need to work with just a few lights at a time. Changing the start falloff value by just 1" can change the intensity of your lighting dramatically.

Now if you are using photometric lights.. I don't have any rational behind the settings as I do for vray or max lights. I believe this may be because photometric lights may have a start falloff value of zero (by default) and this can't be changed. I always find that I usually have to increase the lumen value of a photometric light 2 to 5 times more intense than a vray light or max light. I've have yet to figure out why this is so. Anyone?

Also.. any self-illuminated object that uses a vray light material.. the value of the multiplier for that also need to be experimented with. I have not found a hard and fast rule for what that multiper should be. I think it has something to do with the multiplier you use is the lumens per square foot of surface area of the object it's on.. or something like that. All I know is the material that looks great in one scene.. can suddenly be way to bright or way to dark in another.

Now if you are using a max camera instead of a vray camera.. I have found that the intensity value needs to be only about 3% of what you would use for the vray camera. So if for example you have a 1700 lumen value on a light for the vray camera (equivlent to about a 100watt incandecent light blub), if using a max camera the value would only be about 3% of that or 51. Why? Have no idea.

Then the last thing you need to look at is the color mapping. Another thing you just need to experiment with to see what gives you your desired results. Or set according to LWF, if you are using that process. The color mapping can have a drastic effect on your illumination in the scene.. and weither you are trying to match what your eye may see or what a camera would caputure.. or something totally different.. would guide which type of color mapping to use.

With all those setting set up... then all that's left to do is tweak your camera settings to get the desired exposure. Also.. you need to set the white balance of the camera. I typically try to set the lights up to close to real world settings and then tweak the camera exposure settings and color mapping to get the desired level of illumination rather than to randomly increasing or descreasing the multipliers on the lights.

Hope this helps...

[prey1979]

Mike,

I must say thank you so much for the detailed information!! Im going to take a look at what you have mentioned and try it out... I just have started to play with vray camera been doing it the old max way for years and vray but thought it would be about time to catch up...

thanks again for your time and explanation!

Kidn Regards

Ryan

[MikeHampton]

No problem.

This is just my workflow though. It makes sense to me because the lights (other than photometric) fall into lumen values that make sence once you understand that.. and also then the vray camera settings fall into place of what I would expect them to be if I were taking a real photo of a real envirment that contained the same level of illumination of my scene.

It was wierd at first though to go from the max scan line renderer.. where even the sun was never brigther than a 5.. to a scene were just a 100 watt bulb is 1700!! But now that I am used to it.. the lumen value at least makes sense compared to the now seemingly arbitrary max scanline values.

But I have to add that in my opinion, even with Vray, lighting is still more art than science.. so my workflow is just one of many.

Also, I was just looking through my notes. For a self-illuminated object using a vray light material.. you divide the surface area in meters into the desired lumen output to get the material multiplier. Can anyone verify this?