3dsmax photometric scale?

V-Ray V-Ray for 3ds Max General
1

Can anyone here explain the ‘Use 3dsmax photometric scale’ in the vray 1.50.00 global switches?

Should it be on or off for rendering old scenes?
Does it affect only 3dsmax photometric lights?

2

It does not affect the 3ds Max photometric lights; it affects V-Ray lights and the physical camera. From the manual that I am working on:

“Use 3ds Max photometric scale - when on (the default), this option aligns the VRayLight, VRaySun, VRaySky and VRayPhysicalCamera to the photometric units used by 3ds Max and its photometric lights. When this is off, these plugins operate in the internal V-Ray photometric space, like in older versions of V-Ray. Keeping this option on ensures that a VRayLight with a given power will match a 3ds Max photometric light with the same power.”

Best regards,
Vlado