This tutorial needs you to understand basic use of 3dsmax.
Most people use Radiosity using trial and error method. Some succeed, and some others end up in confusion and frustation. This tutorial will help you to setup light in Radiosity using simple steps. You won't see heavy mathematical calculation here. Just simple calculation which you can use over and over again in other radiosity scene. This technique works best in interior scene. If you are new to Radiosity, look for Introduction to Radiosity tutorial here.
1. First, create 400x800x300cm box. You have to make sure your System Unit is set in cm (Refer to previous tutorial: Introduction to Radiosity System Unit). Apply Normal modifier to the box to flip polygons.
2. Add camera and set your camera view.
3. Add a light. Choose Photometric from drop down list. This type of light is specifically used in Radiosity. The difference from Standard Light is its parameter similar to light in real life. In this tutorial, create Free Point light and place it right below the ceiling.
4. While light is selected, go to Modify tab. In Intensity/Color/distribution rollout, activate lx at (lux at). This way, light intensity is measured in lux. Fill 250 lux at 230cm. When we light a room, you should know what your room function is. Refer table below. There's a list of specific room and its recommended light intensity. Suppose we have a home, an attic maybe enough to use 60 lux, but a living room need 250 lux. So, light intensity may be vary.
| Function | Light Intensity |
| Home | 60-250 lux |
| Office | 200-500 lux |
| Factory | 500-750 lux |
| Public Space | 500-750 lux |
| Museum / Art Gallery | 200-250 lux |
5. Where did 230 cm came from? Usually the height of table is 70cm. Light intensity should reach the height of the table. So 300-70=230cm.
6. Apply Radiosity (go to Rendering>Advanced Lighting>Radiosity). Click OK in opened dialog box. In Advanced Lighting tab, open Radiosity Meshing Parameters rollout. Click Enabled. Next, open Rendering Parameters rollout, and activate Regather Indirect Illumination.
7. Apply standard material to your box. In Advanced Lghting tab, hit Start button, and press Render. You will get well lit room like image below.
7. Last step is setting how much light you need. Make sure your light is selected. In Intensity/Color/Distribution rollout, change Instensity to lm (lumen=luminous flux). Lumen shows how much energy come out of from one single source of light. You should see about 16,000+ lumen. This is the total intensity you should have in your scene. From here, you can calculate how much light you need. Pick up one light bulb or lamp in your house. Watch closely, and you will find light intensity in umen (lm) written. For example I have a lamp with intensity 1500 lumen each. At least I need 10 lamp in this scene. In Intensity/Color/Distribution rollout reduce Intensity to 1500 lm. Then, make clone with Instance method, until you have 10 light.
Note: If you have already decide how much light you must have in your scene. Just split light intensity (lm) until you get total desired intensity.
7. In Advanced Lighting tab, hit Reset All button. And click Start again. Finally, click Render. Your rendered scene should look like before but with more light point. This tutorial is finished. Steps in this light setup sometimes is not totally correct, depends on your model and material. But, this steps should give you basic setting to adjust more further. On, next tutorial we will learn how to lit a real scene.
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