"Light on Vol" setting?

Under the Lighting settings of infotainment system of 2015 Mazda 3, there's a setting called "Light on Vol" which can be set to High, Low and Off. Does anyone know what is this setting for? My guess was that it would be Light on Voltage, so when it's set at High, HID lights receive a strong burst of current so that they can get to the proper brightness right away. On the low setting, it would take them longer to reach full brightness. On the other hand, I find it hard to believe that manufacturer would even offer this kind of a setting.
2017 Mazda CX-5 GT, 2016 Mazda6 iGT, 2014 Mazda3 sGT hatchback
"Vol" = "Volume"
The volume of warning beep when the light is on and you open the door.