Inline Fan - better to install Before or After lights?

I am designing a grow closet right now with 2 400w lights. My question is if anyone has an opinion wheather it is better to install the fan before the lights, or after the lights?

It will be hotter after the lights and this may make the fan life shorter. However, if the fan is after the light it will create negative pressure in the enclosure, making any leaks vacuums, providing extra cooling to the growroom. If I try to extend the fan life and put it before the lights the enclosure will have positive pressure and possibly shoot hot air into my growroom.

Any thoughts or opinions?

tape up all cracks in the light and dont let air get through
run the fan before the lights the air will be way cooler cuz ur blowing air threw the light instead of sucking it threw, which makes more work for the fan

Thanks alot SonomaComa.