Render Tips 2: Exterior Lighting

It is critical to understand the balance of variables of the Heliodon light source to achieve naturallooking perspectives for exterior scenes. The right combination of Heliodon intensity, radiositycontribution and sky illumination guarantee a very impressive perspective.

On the enclosed file called Exterior.atl there are 4 Heliodon sources used. Each Heliodon has adifferent mixture that combines sun intensity, radiosity contribution and sky illumination. The first heliodon --Heliodon 1-- which has only light intensity with no contribution of radiosityand with the radiosity engine turned off, gives the following render result:

As you can see, the perspective is very dull, the contrast between well-lit areas and shadows seemsvery sharp and unnatural. To reduce this effect, we can apply the following: for the first cameraview we activate the camera ambient light, which does not behave like a light source but gives ahomogeneous brightness effect to the whole perspective (this is very useful in providing moreclarity on scenes that otherwise would be too dark). It is recommended however to use thistechnique on low-light scenes since it gives an artificial brightness that can be undesirable on theresult.The second view with Heliodon 2 has radiosity contribution applied with no sky illumination andthus the overall light distribution is already much better, but still not satisfying.

The third view uses Heliodon 3 that explores another very significant variable: sky illumination(the light received from the sky as a whole). In this exercise we apply a sky illumination as if it wasa totally cloudy day with no direct sun perceivable.

The last view uses Heliodon 4 which combines both components: direct sun light with overall skyillumination. As a general recommendation for exteriors, the sum of direct light and skyillumination percentage should be between 100 to 130 on most cases, otherwise the scene may beunder- or overexposed.

Notes: when using an image as a background, make sure the image matches with your model's lightrequirements, since a direct sun scene may conflict with an afternoon sky or could result inundesired output, as shown below:

Until now we have been applying the value of 100 on the radiosity engine. Sometimes, however,when you have more shaded areas on the exterior scene, it is advisable to increase the radiosityvalue to obtain a better light distribution, as in the following example where the 200-value wasused:

Good luck! Hoping these tips will help you in getting better render results!

Author: Sergio Rodriguez