My opinion -always taken with a grain of salt - is that there's too much ammonium
(or urea decomposing to ammonium,ammonia & diurea ... ) in her "diet"....
N is assimilated in two forms : Nitrate ion (NO3 ) and ammonium ion (NH4 ) .. A healthy ratiobetween them would be somewhere close to 3:1 ,respectively...
There's,probably, a great deal of photosynthesis going on ,with those lights...
So,great amounts of N ,are assimilated,also ....
If ammonium ion is more ,it does not get stored and it is used at once....
But photorespiration and photoinhibition slow down the rates of photosynthesis,at a certain point and afterwards ...
Assimilated N can not be "used" all and being ammonium it can not be stored in the plant's vacuoles (inside cells ) ..
So part of it remains to the leaves(inside cell liquid ) at high concentrations and through osmotic pressure ,dries up the leaves...
( Cell pumps up with water till it explodes =>dead cells =>brown spot areas ...
Rest of transcellular matrix dries up.Water was used by cells which exploded..
And then,water evaporated into atm. air ==>Leaves /leaf tips "curl" ...)
Another part is becoming ammonia and escapes to atmosphere..
(Does it smell ammonia in the grow,sometimes ?
If yes ,it might be a good sign of too much ammonium /urea is used , in the nutrient "diet ".... )..
That's from humble me...
Logodiarrhea...
I get it often from high quality led bud....