TurboCAD's traditional lights (those accessed via the "View Lights" dialog) and luminances are more similar that most users suspect. They can be made to behave identically in respect to the amount of light they produce and they way the light impinging on an object varies with its distance from the light or luminance.
As delivered, the power settings for traditional lights is effective only when using radiosity rendering. The ability to vary the power in other quality rendering modes can be turned on with a small edit to the TCW90.ini file (normally found in C:\Program Files\IMSI\TCWP90\Program\).
To turn this feature on, close TurboCAD, open TCW90.ini, and search for "LIGHT_POWER_ENABLE=0". Edit the entry to read "LIGHT_POWER_ENABLE=1" and save the file.
Note: The entry will not appear in TCW90.ini until at least one draft or quality render is performed.
With this feature enabled, the output of a traditional light, with a power of 1 Watt and with lumens set to 255, will exactly match the output of a luminance set to an empirical value of 1.
The settings described in the version 9 discussion above are turned on by default.
Light fall-off settings are also identical for traditional lights and luminances. The problem is that they use different nomenclature. The following table shows how the settings are related:
| Light | Luminance | Formula | Notes | |
|---|---|---|---|---|
| 1 | No Attenuation | Constant | 1 | The light falling on an object does not vary with distance from the light source |
| 2 | Linear | Inverse no clamp | 1/D | The light falling on an object varies inversely with distance from the light source, rising to infinity at zero distance |
| 3 | Natural Linear | Inverse | 1/(D+1) | The light falling on an object varies inversely with distance from the light source, rising to unity at zero distance |
| 4 | Quadratic | Isl no clamp | 1/(D×D) | The light falling on an object varies inversely with the square of distance from the light source, rising to infinity at zero distance |
| 5 | Natural Quadratic | Isl | 1/(D×D+1) | The light falling on an object varies inversely with the square of distance from the light, rising to unty at zero distance |
The following graph shows how the intensity of illumination of an object varies with its distance from a lightsource for the above five fall-off settings. Distance is in meters and intensity is relative to the "No Attenuation" or "Constant" settings
The following is the same graph expanded near the origin.
