Light Sources
For the radiosity calculation, the point light, spotlight, directional light, distribution light, area light, linear light, distant light, and sky light properties are used.
The ambient light parameter of the Distant Light Window and the Lighting Factor parameter of the Background Window are not used.
Point Lights and Spotlights
From the Light Attributes in the Object Info Window, the Intensity and Spotlight Angle parameters are used.
From the Surface Window, the Diffuse Color parameter is used.
Area Lights and Linear Lights
The value of the Intensity text box and the states of the Lumen and Visible checkboxes in the Object Info Window for line objects, and the Diffuse Color setting in the Surface Window, are used for the radiosity calculation.
Distant Lights and Sky Lights
The values for the intensity, direction and color, and the settings for the sky light specified in the Distant Light Window, are used for the radiosity calculation. No ambient light is used.
The distant light and its intensity can be interpreted as sunlight. Sunlight and sky light are sometimes referred to together as total daylight (or global luminance).
In the radiosity calculation, the surfaces onto which mostly the total daylight (sunlight and skylight) is emitted are first calculated, followed by the surfaces receiving direct artificial lights (point lights, area lights and spotlights) and then the surfaces catching indirect light. For the calculation of indirect light, the surfaces that catch more light will be computed first.
The table below shows light types and their typical intensities.(Units: lumens)
| Type of light | Total luminous flux |
|---|---|
| 60W incandescent lamp (white) | 810 |
| 100W incandescent lamp (white) | 1520 |
| 50W tungsten halogen lamp | 1000 |
| 100W tungsten halogen lamp | 1600 |
| 15W compact self-ballasted fluorescent lamp (day light) | 780 |
| 10W straight-tube fluorescent lamp (white, 330mm long) | 460 |
| 15W straight-tube fluorescent lamp (white, 436mm long) | 820 |
| 20W straight-tube fluorescent lamp (white, 580mm long) | 1160 |
| 30W straight-tube fluorescent lamp (white, 630mm long) | 1700 |
| 40W straight-tube fluorescent lamp (white, 1198mm long) | 3000 |
The total luminous flux of the sun and the average distance between the earth and the sun are as follows:
1.967 x 1028 lumens
1.496 x 1011 m
However, the light intensities under direct sunlight and under indirect sunlight (fair sky) are considered to be approximately 100,000 lux and 10,000 lux, respectively.