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Working on a candle project to practice:

Under the 'world' properties I have turned the strength down to 0 (thus making it pitch black). I then added a lamp to the workspace and adjust its strength to 1-2 (doesn't matter) and it starts lighting up the candle. If I adjust the strength too high the candle starts getting over-exposed looking and just stark white, but the ground remains mostly black. You can BARELY see the ground's reflective surface, but the sun lamp seems to have no affect on the ground.

If I remove the Glossy BSDF property from the ground the ground then reacts to the sun lamp as expected, immediately getting brighter to match the lamp.

What could be causing this? Shouldn't reflective surfaces still brighten up a bit when a lamp hits them.

On the left you have the exact same image, nothing changed except for the properties of the ground with (left) and without (right) the Glossy BSDF characteristic. (which expands beyond the entire image).

enter image description here

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I think your problem is that light is being reflected of the ground plane, but not into the camera. (see specular reflection)

Shouldn't reflective surfaces still brighten up a bit when a lamp hits them

It's not a matter of "brightening", the light has to hit the plane and then get bounced into the camera.

Diffuse objects scatter light, so they bounce some light into the camera regardless of the angle. Completely glossy objects (no Roughness) will bounce light without scattering it at all, and slightly rough glossy surfaces will scatter light slightly:

enter image description here

To visualize this in 2d:

enter image description here

As you can see, the camera will not receive any light from the (slightly rough) plane. Except for light reflected of the diffuse object:

enter image description here

Workarounds:

To work around this, you could:

  • Add more lights. You could add a light in front of the camera and behind the object which bounces light off the plane into the camera:

    enter image description here

  • Increase the world background brightness (in the real world there is almost always some ambient light) You could make it so the world appears black to the camera while actually emitting a little bit of light by means of the Lightpath node:

    enter image description here

  • Add a tiny bit of diffuse reflection to the glossy shader:

    enter image description here

    The diffuse shader input color brightness controls how much diffuse is added. (black is none)

  • Mix some diffuse reflection into the glossy shader. (with a mix shader) Note that this is slightly different than adding.


Replies to comments:

Thank you for this great response! Unfortunately, adding additional lamps on the far side of the object has absolutely zero affect on what the ground looks like. The ground has not seemingly changed one pixel with the addition of another lamp or with the moving and re-adjusting of the lamps and their strength. It HAS affected the candle though, and the candlestick has a glossy finish, so I don't understand why the planar floor won't do what the candle base is doing.

It depends on the angle of the surface and the camera. (and the type of lamp)

To get a feel for this you might want to try playing with the view (with viewport rendering on) with just the plane and a couple lamps to get an idea of how this works.

I should add that I wanted the candle to appear to be the only light in the room. I made the flame an emission source and that lights up just fine, but when the candle and candlestick are lit up but the floor is not it just looks weird

In that case you probably don't want to add extra lights. (you might even want to remove all the lights except for the candle flame)

Keep in mind that in an actual room there is some indirect lighting from the walls and other objects. You could set the world to a very dark color (but not black) to simulate this.

In the end you were right. I had my floor as a glossy surface, with a roughness of .100 which apparently makes the surface too glossy to reflect light? I had to make it a .2 or higher to get any sort of light reflection off the object. Although I feel like even a polished brass sphere should glow when a light hits it.

Again, an object is only visible when light bounces off it and into the camera. AFAIK, there is no such thing as "too glossy to reflect light", it's just not reflecting light where you want it. (i.e. the camera)

The reason increasing the roughness makes reflections more visible is that it scatters light in more directions, increasing the probability that some light will enter the camera.

I think the solution you want here is to mix some diffuse reflection into your glossy material. This will bounce light in pretty much every direction, making sure everything is visible to the camera.

If I had any questions left, I'd ask if there's a way to adjust the intensity of an emission source that isn't actually a lamp? As it stands I have the flame set as an emission 'texture' but i put a lamp inside the object and adjusted the lamps brightness to compensate for the flame's lack of brightness.

I'm not sure what you mean by emission texture, but if you are asking what I think you are asking:

You can make an emission shader that appears the color set in the Color input while emitting more light than a Strength of 1:

enter image description here

Only an emission shader with a strength of 1 and 20:

enter image description here enter image description here

With the above node setup:

enter image description here


Example renders:

Completely black world with some diffuse mixed with the glossy materials:

enter image description here

Completely black world with only glossy reflection:

enter image description here

Only glossy with a mesh light (selected) affecting the glossy floor:

enter image description here

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  • $\begingroup$ Thank you for this great response! Unfortunately, adding additional lamps on the far side of the object has absolutely zero affect on what the ground looks like. The ground has not seemingly changed one pixel with the addition of another lamp or with the moving and re-adjusting of the lamps and their strength. It HAS affected the candle though, and the candlestick has a glossy finish, so I don't understand why the planar floor won't do what the candle base is doing. $\endgroup$ – leigero Oct 31 '13 at 3:57
  • $\begingroup$ I should add that I wanted the candle to appear to be the only light in the room. I made the flame an emission source and that lights up just fine, but when the candle and candlestick are lit up but the floor is not it just looks weird $\endgroup$ – leigero Oct 31 '13 at 4:10
  • $\begingroup$ In the end you were right. I had my floor as a glossy surface, with a roughness of .100 which apparently makes the surface too glossy to reflect light? I had to make it a .2 or higher to get any sort of light reflection off the object. Although I feel like even a polished brass sphere should glow when a light hits it. $\endgroup$ – leigero Oct 31 '13 at 4:40
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    $\begingroup$ Have you tried putting it in an actual room with diffuse walls? In the real world they are responsible for reflecting light back to the object. $\endgroup$ – cybrbeast Oct 31 '13 at 10:56
  • $\begingroup$ @leigero It depends greatly on the angle of the camera and the reflecting surface. See my edits. $\endgroup$ – gandalf3 Oct 31 '13 at 19:31

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