Thanks @ILGM.Zoe for passing us the puck 
You have to begin to worry about lumens when their total in square feet give you more than 100 000 lux, the peak of the sun…
The total amount from the sun hitting the ground is around 1120 W/m2.
Direct sunlight has a luminous efficacy of about 93 lumens per watt of radiant flux. This is higher than the efficacy (of source) of most artificial lighting (including fluorescent), which means using sunlight for illumination heats up a room less than using most forms of artificial lighting.
Multiplying the figure of 1050 watts per square metre by 93 lumens per watt indicates that bright sunlight provides an illuminance of approximately 98 000 lux (lumens per square meter)
You have 80 000 lumens/16 square feet and by doing some calculation with the help of this site :
you have around 53 800 lux total for your growing space. However, a fluorescent do not have the PPFD/PAR (intensity) needed to go deep in the canopy and will lose half of it’s intensity at each foot or so if not more.
So, to resume, like @dbrn32 mentioned you’ll have to keep your t5 very close to the canopy, around 6 inch away, due to the lack of intensity of fluorescent, and you should be good without fear of light burn, and if you can do a SCRoG setting, it will be best… And have tubes between 2700-3500K warmth for flowering stage…
(Lumen are usualy taken at 1 foot distance)
Hoping that’s respond to your question, dear customer, why not join our friendly community !?
~Al 
P.s. @peachfuzz have great experience with fluorescent too, maybe he will add his 2 cents too
