Illumination Tutorial

Dear Architects and interior designers, this is one of my tutorials that I wrote for my students at the Florence Design Academy ( This tutorial is about illuminating a room using sunlight, which is coming through a window (ideal for living rooms, kitchens and bedrooms).

There are many different illumination techniques that I teach, on the topic of interior-rendering. This one is quite easy, and will use 2 different kind of lights. One is the MR Spot Light and the other is the photometric Free Area Light. Before we begin, it's very important to inform you that we will use mental ray as a render engine and 3d studio Max 8.

Mental ray is a very stable render engine, and it allows us to achiece very realistic renders. Since we are using Mental ray for this tutorial it's also very important to use real measurements when creating all the interior/furniture, otherwise the result will not be optimal. It would also be important to already have a bit experience using mental ray and it settings, as this tutorial will not go into explaining all the settings we use (settings about rendering and materials are in other tutorials of the FDA).

The first light (MR Area Spot light) must be located outside the room and you must move the target of the light through the window and place it inside the room as we can see in the image to the right.

I use a value of 0.8 in the multiplier slot, but this doesn't mean that you must use the same number as later we will add some more lights which will influence the brightness of the room. Also change the colour to a very bright orange-yellow, to simulate the Sun rays. In the Area light parameters (modify panel) you have the possibility to make the shadow softer by increasing the size (hight,width) of the light. To give the impression that outside the room, the environment is very bright like in the image to the right, you must create a big white self-illuminated box in front of the window. After this step select the MR Area Spot Light and exclude (In the Exclude-panel from the modify panel) the self illuminated box from illumination + shadow casting. Otherwise it will create a shadow in the room. Now try to make a will be quite dark.

Right, how can we make our render more realistic?....Go to the Render Scene Panel, and choose indirect illumination, and check the Final Gather box. Put a low number in the Samples slot (like 50) and make a quick test render and see the difference. It will be similar to the image below.

First rendering with only a  MR area spot light + Final Gather enabled

First rendering with only a MR area spot light + Final Gather enabled

For a much higher quality, you must increase the number of samples. In my render I put 600 (this will make the render time much longer). Don't put more than 1000 samples, as you don't need such big numbers for a final render. Try to go up with the number, making small test renders as you go. First try 150...than 250... than 400 etc.

Let's increase the realism of the render. Still under the final gather, there is a slot called - trace depth - max bounces, where we can increase the number. Let's put 4, never use more than this, because it will really take a long time to render). This option sets the number of times the diffuse light bounces are calculated for a single diffuse ray. In other words; it allows us to have the same energy that we can see when sunlight is illuminating a room.

Now you should have more or less the same result in as in the image below.

Rendering with only a  MR area spot light and max bounce 4

Let's add a new light.

MR area spot light + free area photometric light

MR area spot light + free area photometric light

Create a Free Area photometric light (without shadows) in front of the window (it must be inside the room).The size should be a bit smaller than the window. I set the luminosity to 1500 CD. Try to make experiments reducing and increasing the intensity. The illumination depends also on the size and the position of the lights that you are using. You should now have a rendering like the image below.

Rendering with a MR area spot light + free area and max bounce 4

The illumination is quite good for now, but we must give the impression of more luminosity. It becomes dangerous if you try to increase the first 2 lights by too much, as you will run the risk of burning all the renders. We can improve the render by adding a last light. Create a free area photometric light in front of the Room. Normally I delete a wall and create a camera inorder to get a better render of the interior. So now, create a free area photometric light (without shadows) in front of the deleted wall like in the image below.

The size must be smaller than the size of the wall that you have deleted and don't locate it too close to your room. Leave a small space between the room and the light, otherwise you will burn the surfaces which are too close to the light. I put around 850 CD in the slot for the Intensity. Try to make a test render. You should have a result like in the image below.

The result of the luminosity depends not only on the intensity but also on the size of the light that you create. You will notice that increasing the size of the area light you will have more or less the same effect as you would if were increasing the intensity number. The last step that you can do to improve the realism is to add a glare filter. This will give a glowing/shiny effect on the brightest parts of your surfaces. Try to always change the settings inorder to try and discover the optimal balance of size/location/intensity of the lights. I tried this tutorial with success also on interiors with more than 2 windows...for each window add a small area light and a spot light.

Problems, errors and solutions : If your render is way too dark, you probably need to just increase the intensity of your last free area light, or you must increase the size of the free area light.

  • Colour-bleeding effect : To avoid this effect put a lower number in max bounces.
  • Long render times : This kind of illumination requires a really long render time. To spend less time you can reduce the max bounces number to 1 or 2 and make all the lights a bit brighter.
  • The rendering is full of big dark dots : This happens if in final gather you have a low number in the samples slot.
  • If you have the imperfections you see in the image below, after you have increased the number of samples try to add a bigger number in theFinal Gather Radius slot.

How to have very fast test renders : Make the render size small (example: 100x75 pixels). It will be for sure too small to see any details, but you can clearly see if the illumination of the room is too dark or too bright.

Note: Remember that this tutorial teaches a technique of illumination, not what values to put in the light parameter slots. Since the final result of the renders depend on the size of the room, the intensity, the colour, the size and the location of the lights, you must do as many test renders and experiments to get the correct values as you feel is nessessary.

I hope this tutorial was useful for you :)....Best regards

Mario Malagrino

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