Lamp shade material?

[sharktacos]

Sorry, if this is a FAQ, I've searched the forums and manuals only found minimal information on this.

I've been experimenting with creating a lamp shade material. I have a 2SidedMaterial with vrayMaterials in the front and back slots. The lamp shade geomentry is single-sided, and has a vraySphere light inside of it which illuminates it from the inside (the way all lampshades work).

With the default VrayMaterials in each slot of the 2SidedMaterial I only see the lamp shade illuminate, but the lamp does not light the room at all since all light is blocked by the shade geo. To get it to work at all I need to make the refraction color non-black, and turn on Affect shadows.

When I do this however the room is only dimly lit, while the lamp shade gets completely blown out. The opposite should be the case: a well lit room, with subtle translucent illumination on the lamp shade. Some thing like this:


How can I get this effect? Are there any tutorials that cover this? I am interested in a relatively physically accurate solution with reasonable render times. What I would like to avoid is the "lamp with the light outside the lampshade" approach.

[Metzger]

You can model thickness to the geo with UV's then bake out the Subsurface shader, then re-apply it as a light material.

[sharktacos]

That's an interesting approach, but in order for the light material to illuminate the room in the way a lamp would in real life, I'm pretty sure the light material lampshade would need to be high intensity, and thus end up looking blown out too. What I would like is for the lampshade to look like the above image, but illuminate the room as it does in the above image.

[Tobbe]

Hmm, isn't this an exposure kind of problem? Exposure for a well lit room usually blows lights as this... you could play with the color mapping parameters to squeeze the hilights a bit.

[aweidenhammer]

Yes, I think you're having an intensity or exposure problem. It works fine for me. The sampling is much less efficient, since you are now lighting via a mesh shape, but it does illuminate my scene... and I've fully enclosed the bulb.

[sharktacos]

Andrew, When you say you've "fully enclosed the bulb" is the bulb a light or a mesh shape? What are you doing for the lamp? Is it a material (like 2sided) or is it a light mesh (which would mean it is not enclosed since the shade becomes the illumination source)?

Could you post a pic, or even possibly a scene file?

As far as exposure goes, I'm lighting with the linear lighting settings described in the Nederhorst guide. I am not however using a physical camera if that it important.

[djx]

I agree with the advice already given.

I think I would probably just try to add some direct lighthing with an invisible sphere light casting diffuse light from the location of the lamp, but unlink the sphereLight from the lamp shade. Combined with the other suggestions, this could get around the requirement for high samples on the light material, and give you more control over the general illumination.

I have to also add that It looks to me like your reference image has a big window providing a lot of the illumination in that room, does it not?

[sharktacos]

I agree with the advice already given.

I think I would probably just try to add some direct lighthing with an invisible sphere light casting diffuse light from the location of the lamp, but unlink the sphereLight from the lamp shade. Combined with the other suggestions, this could get around the requirement for high samples on the light material, and give you more control over the general illumination.

I have to also add that It looks to me like your reference image has a big window providing a lot of the illumination in that room, does it not?

Yes, I know that I can cheat this by having additional lights, but this gets problematic with shadow casting (all CG cheats have their inherent drawbacks and limitations). So I was hoping that it could be done in a more physically correct way with vray (the bulb behind the lamp actually lighting the room).

The picture does have a window, so it is not a perfect example. It's just something I could find quickly as an illustration. However, I'm sure we all have lamps in our houses where the lampshade looks like the pic and the room gets illuminated enough to not trip over the couch . That's what I'm after here.

Just to clarify: I can make the lamp shade (geo) look like it is illuminated by the bulb (sphere light). But then that same light does not illuminate the room as a real lamp would. If someone else is able to get that to work, I would love to see it.

I can of course make another sphere light to do that, and maybe use light linking so it does not affect the lamp (which would cause problems with the shadows). I was trying however to get it to work with just one light, like it works in real life.

[Metzger]

That's an interesting approach, but in order for the light material to illuminate the room in the way a lamp would in real life, I'm pretty sure the light material lampshade would need to be high intensity, and thus end up looking blown out too. What I would like is for the lampshade to look like the above image, but illuminate the room as it does in the above image.

Yeah, but you have material overrides on all shaders. You can actually have one light material with a lower intensity then have the beauty rendered light material render whatever you want.

[sharktacos]

I can see how that work would work well as a nice workaround.
I guess I'd like Vlado or someone from vray to confirm that the best approach is to continue to use these tricks in this case, rather than having a more physically accurate solution?
I know that in general, vray attempts to do accurate simulations with its render. Is this case an exception? Is it something that is currently too difficult (i.e. too slow) to emulate in the render?

[aweidenhammer]

Sorry for the delay.

I created a sphere light, placed it inside a cylinder, raised the intensity of the light quite a bit (1000 defaultUnits, I think), put a 2-sided material on with white lambertian for front and back, raised the transluc slider to the max and rendered in RT to start. No other lights to start with, and no physical camera. I built it into one of my test room scenes, that is set to proper scale.

when I say "exposure" problem, it may just be you need to crank up the light's intensity quite a bit... but what works to illuminate the room as a normal light bulb, should also work inside a 2-sided-mat cylinder.

When in doubt, eliminate all other factors/lights.

[sharktacos]

Andrew, could you post a pic of your result?