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Tutorial
Welcome to the fifth and final part of the indoor lighting tutorial series. This time the work will be easier since we will just set up and use one light and then concentrate more on the overall look of the image rather than the lights' parameters.
Let's get started. Open the "NIGHTTIME03_Start.mb” file. It's almost the same as in the previous parts of the tutorial. The only thing that has been changed is the TV screen shader to create a self-illumination effect (Fig.01).
Create a new Area light and position it in front of the TV screen (Fig.02).
In Fig.03 you can see the exact values used for the light's position/rotation/scale. Make sure it's pointing outward.
Assign a blueish color to the Area light (the RGB values used in the scene are: 0.558, 0.564, 1) and enable Raytraced Shadows. Do a quick render test (Fig.04).
As you can see, the TV screen is our main (and only) light source in the scene; the opposite walls are being lit by the screen, while the back wall is totally dark. This is a good starting point for this kind of illumination, but we still need more light in the scene, even if it is a night time situation and we have only one light source.
Open the Render Settings panel and switch to the Indirect Lighting tab. We'll use some GI to make some more light bounce all over the room. Enable Global Illumination, set its Accuracy value to 200 and the Radius/Merge Distance values to 3 and 1, respectively (Fig.05).

Fig. 05
Go back to the Area light's properties, enable Emit Photons and copy the RGB color you set earlier to the Photon Color swatch. Also set the Photon Intensity to a higher value, like 100.000, and the Global Illumination Photons value to 1.000.000 (Fig.06).

Fig. 06