I'm trying to create soft lighting through non-bumpy frosted glass. This is my attempt and it's not really working the way I want it to as reflections have no blurriness and not the kind of blurriness I'm going for:

My attempt. reflections have no blurriness and not the kind of blurriness I'm going for

All relevant information is in the screenshot.

I have used a cube as a light source inside the structure. There is a plane (thick) in front of and behind the cube light.

Changing the roughness to max doesn't get me the required result either. Also, at higher IOR values, the cube is only about halfway visible then just cuts of from this perspective. The shape of the light on the wall behind is a hard circle which makes no sense to me.

Another problem is, the reflections do not have the blurriness of the glass. I think that has more to do with the material of the floor which is a simple glossy and diffuse shader mix with Fresnel as input to the mix shader.

Here are some images of the material I'm going for, taken from Stanley Kubrick's films :

Soft lighting with shape of the source behind it barely visible. Bartender scene from 'The Shining'

Another still from Space Odyssey.

enter image description here

I would like to be able to control the softness of the light behind the source by changing parameters of the glass in front of it.

This is my first post on stackexchange and only 3 days using blender so I'm pretty new to this.

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    $\begingroup$ I think the fundamental problem here lies in the material type, those reference images don't show clear glass, but more like an opaline translucent surface. Try using a Translucent shader instead of glass, you may get results closer to what you expect $\endgroup$ – Duarte Farrajota Ramos Aug 6 '17 at 13:20
  • $\begingroup$ Tried that. It doesn't work. I mixed with diffuse for a softer look but the problem is that, with it without diffusion, the material doesn't show light beyond a certain level, even if I change emission of the cube light to crazy high levels $\endgroup$ – Jairaj Patil Aug 6 '17 at 13:47
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    $\begingroup$ I guess the answer below proves it does work $\endgroup$ – Duarte Farrajota Ramos Aug 7 '17 at 0:00

Use a mix of glass and translucent shaders. To control how blurry the light source behind the glass is, play with the factor values on the mix and the roughness of the glass shader.

Here's an example of an emitter object enclosed on a glass cube. The glass walls have to have some thickness (you can use a solidfy modifier) so that it is not a solid glass cube.

enter image description here

An other factor that will have a great impact in the light effects you are after, is the color transform used in the color management settings. Being able to use a bright light source and a much larger dynamic range for the image, will help you have a more realistic result. Experiment using the filmic blender colour tranforms.

enter image description here

(Click on the images to enlarge)

Read also:

Render with a wider dynamic range in cycles to produce photorealistic looking images

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    $\begingroup$ See also: blender.stackexchange.com/questions/66047/… $\endgroup$ – cegaton Aug 6 '17 at 21:10
  • $\begingroup$ this gets pretty close. This was what I tried first by instinct; translucent and glass shader. A problem with this however is that it makes no difference whether my light source is at emission strength 5000 or 200000. The amount of light passing doesn't increase after a certain point. I am using filmic blender already that was the first thing I installed thanks to blender guru's video and being fairly knowledgeable in the filmmaking area. Also, I was wondering if subsurface scattering could be mixed too in the node setup (seeing the above link which also gives a good result) $\endgroup$ – Jairaj Patil Aug 8 '17 at 9:15
  • $\begingroup$ @Jairaj, I don't know if this will help or not but the Emission shader is one (of the few) that you can plug into the Volume input of the Material Output node. So try making a cube with a Translucent node (mixed with others or not) plugged into the Surface and an Emission node plugged into the Volume. $\endgroup$ – lumpynose Aug 8 '17 at 17:46
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    $\begingroup$ @JairajPatil please show something that shows what you are doing. Changing the strength for the emissions definitely has and effect, and you can take it up to the point where everything is white... $\endgroup$ – cegaton Aug 9 '17 at 2:11
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    $\begingroup$ @cetagon here are some screenshots imgur.com/a/3uaRx $\endgroup$ – Jairaj Patil Aug 9 '17 at 12:57

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