|Christian Bauer; 10/2002|
With Viz4 Autodesk introduced Radiosity to it's very popular line of 3D applications.
With Max5 you get a similar engine which is much faster and have some new features.. anyway, this tutorial is for viz users but maxusers will find parameters on the same place but without the correct units.
In this tutorial i will show you how to setup radiosity and create selfilluminated materials.
First i want to point you to one problem some of you will have, since we now
have to work in RL units.
If you want to use radiosity you should always use models which are scaled to it's real life size. We also use light which use real illumination data, like IES which have a FIXED brightness (mostly in cd/m2 ..candela per m2)
Our test room is 4m x 5 m and have a height of 2,5m ..i think you will have a room like that, next to you, so it's a way to explore how the light should be.
I put a "Normal" modifier over the box to flip the normals.
If you want to insert a window and use daylight, i would suggest you to fully model the room with all the walls around the room since VIZ/MAX will light the room through the edges until you change the shadow bias of your sun.
Anyway.. next we create a line with thickness, which will be our lightsource. you can see the settings of the line below:
The next task will be the material: choose a slot and change the illumination
type to color and then choose any color you want. This will be the lightcolor.
When you are finished with this task we have to change the material to "Radiosity override" since we have to setup the strenght of the light.
Choose "Radiosity Override" and keep the old material:
You can still access the basematerial where you can change the color or transparency.
Now we have to choose how strong the light will shine.
To explane the value, i want to give you some other values from real life:
If you sit in an office your table will be lit by many lights and maybe the building company have decide to ask a lightdesigner to plan the lightsetup for them ... then you can be sure that on your tables to surface will have a brightness of at least 300cd/m2. The table is not a lightsource but you now know how bright 300cd/m2 are. With this in mind you know that a illumination of 300cd/m2 will be not enough for a lightemitting object. Now have a look at IES files. IES files are lightdistributon descriptions which also have a brightness value ..mostly in lumen or candela. These lightsources are pointlights and have a value for a 1m2 area in 1m distance from the lightsource, but we maybe get a feeling of how strong one light can be which will be in an array of ~80cm -1m to the next light. I would say most lights are in the range from 900-2000 cd and so we can say that our maximum illumination shouldn't be more than 2000cd/m2.
Now we can say the luminace could be from 300-2000 cd/m2 but this value should be variable since a small room will need less light than a big room. Also the size or lenght of your lightemitting object will change the brightness. I will start with 1200cd/m2 which seems to be enough for our small room :
So.. material is ready and now we have to setup the scene:
We start with the radiosity window: there is nothing much to say at the moment, because we first have to setup the exposuresettings
I suggest you to use the Logarithmic Exposure Controll since it's the most flexible at all. You can change brightness and contrast later (when you have your first testrendering with radiosity).Iif it's an exterior scene (with max5 you can use Lighttracer for exteriors) you should select daylight and if your scene is lightened by daylight through windows then you have to select daylight. When you are ready you can go back to the radiosity window and setup the subdivision.
In the radiosity window we now have to setup the subdivision, because radiosity uses the mesh to store the lightinformations and if there is not enough mesh you will get a very flat and disapointing result. I choose a subdivison size of 20 cm. This means that viz will add every 20 cm a triangle mesh. This produces many faces and the resulting mesh can be hard to handle with slower systems. Until Autodesk do not introduce adaptive subdivison you should be aware of this problem.
Now we are ready to start the calculation. Please note that we do not have setup the wall material which will result in not accurate lightdistributon. If the result is too dark you can now change the brightness in two ways: You can change the brightness of the light or you change the exposurecontroll. If you are working with IES lights, then you should add another light or change the exposurecontroll, but NEVER change the strength of the light... IES files are 100% correct and provided by the manufactor, so you can trust the values.
above you see that the selfilluminated line is dark , but don't care about it, if you render the scene everything will be fine:
hope this was an inspiration to you *g*
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