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So, I'm trying to create a chemical plant model, and you know how when you drive past an oil refinery at night it's all lit up with dozens of lights and it looks really cool?

That's what I'm going for, but the problem is, my model is HUGE! And when I make the sphere that asks as the light bulbs and I only add a basic emission shader it doesn't give off enough light and if I increase the strength it only makes the light more intense.

You can see here, the light isn't giving off anywhere near enough light:

image of blender light emitting object

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    $\begingroup$ Try using the default lamp objects instead of only the emission material. $\endgroup$ – Ezra Sep 5 '17 at 20:59
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Mesh lights can be useful but they are quite an inefficient way to light your scene - especially with a large number of small lights as in your case. A better solution is to use Point Lamps to light the scene - although those are not visible to the camera which is not the effect you are looking for.

The solution is to use a Point Lamp embedded in the center of what would normally be your mesh lamp. This way the scene is lit by the Point Lamp (and can take advantage of all the optimisations in the renderer for handling point lamps) while the mesh lamp is still visible to the camera - but is set up to not block light from the lamp.

You can achieve this using the following material :

material

The Is Camera Ray light path input is used to switch between a Transparent shader and an Emission shader depending on whether visible to the camera. This means that for illuminating the scene the mesh will be invisible (so the lamp is visible) but in the actual render the mesh will emit light as if it were lighting the scene (so any effects in compositing (such as a Fog Glow) will still take account of the brightness).

As a comparison, here is a scene using a mesh lamp with 20 samples. The lamp on the right is a Point Lamp (and so is not visible) while the one on the left is a mesh lamp and so if visible to the camera. Note how the mesh lamp is very poor quality. Many more samples would be required to get acceptable results.

mesh lamp

Using the above material produces the following result. Note how the mesh lamp is still visible but that the Point Lamp (positioned inside the mesh and set with a similar size as the mesh) is providing the actual illumination. Again, this is with only 20 render samples but the result is much more pleasing than the mesh lamp.

faked mesh lamp

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There is already a great technical answer on how you should use a real light instead of a mesh to light the scene. So I will go into the artistic side a bit more:

When you see a strong lightsource, what you are actually seeing is:

  1. How the nearby surfaces are lit by it. -This can be accomplished by just cranking up the energy value of the lamp.

  2. The light is scattered due to the air and dust around it. This is what creates a visible beam or halo around a light source. - When used subtly, it can convey a lot about the intensity of the light.

  3. When the light goes through the optics of a camera, it scatters again. The intensity and size of the glow is critical in conveying the brightness of the lamp.

enter image description here

In this before/after, the ember on the right appears much brighter simply due to bloom and scattering.

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