Install Radiance V then you can adjust the values below:
Go to
GTAV / mods / Update / update.rpf / common / data
find visualsettings file. Make sure Edit is on in OpenIV. Right click the file and select Edit. If it wont let you select edit drag to your desktop, then make changes and drag it back in (cant remember if it allows editing in OpenIV). Look for these below:
car.defaultlight.day.emissive.on
car.defaultlight.night.emissive.on
These are Radiance V default Values
car.defaultlight.day.emissive.on 1700.00
car.defaultlight.night.emissive.on 1100.00
Obviously the higher the brighter