Hi,
The Arnold Spot Light has a Lens Radius to simulate a collimated beam. Neither Standard nor Photometric 3ds Max lights have this feature.
Since all real-world spot lights have lenses and/or reflectors to focus the light and reduce the amount of decay over a given distance, the lack of this feature means that it is not possible to accurately mimic a real-world spot light in Quicksilver or in third-party renderers, e.g. V-Ray.
However, there is a very simple fix: NEGATIVE DECAY START.
If the Standard Spot Light "Decay Start" parameter could go into the negative range, it would push the virtual light source behind the light gizmo, giving the same control over decay as the Arnold Lens Radius. It wouldn't change the shadows or suffusion, but it would give us full control over decay.
Likewise with the Photometric light. There is currently no Decay Start parameter at all. Photometric lights always obey quadratic decay, even though actual real-world spot lights do not work this way. This is a limitation that makes it impossible to do accurate lighting studies or properly art direct shots. Please add a Decay Start parameter and allow it to go into negative values. Combined with the Shape and Distribution parameters, this would allow artists to emulate almost any type of light.
Thanks,
Aaron
