No matter if its no cp or cp, you should never have less then 20k imo. I try to aim at around 22k as a bare minimum.
Remember with Light Armour build you will be reliant on wards, 100% uptime to avoid Crits. This also means in essence your HP pool can be lower as its covered with a health ward
No ward on light armour means dead, especially if you don't have full Impen protection