it cant be mites because of the pattern. mites would take the chlorophyll from patches all over the leaf, not on the tips.I have the same except just white/yellow small tiny scratches clost to the tip. I would think spider mites but not sure. Get that 30x micro and look under the leaf for small eggs if you find any just grab an organic pesticide and spray the mother fuckers.
the answer lies with this man/woman water was on the plant, i call it scorching, this acts like a magnifying glass under sunlight, and sitting above the palm of your hand move the magnifying glass closer until the sunlight starts to get smaller and when it gets to a small bright dot on your hand it will start to burn, in this case the heat from the lamp is slowly cooking the leaf ,it is either that or the leaf touched or got too close to the lamp, if the plant had any health problems it wouldnt just be on one leaf and other plants would break out with the problem too at the same time or within hours. at least that is my opinion.That is a burn IMO, I have had leaves that look exactly like that, water got on the leaves during watering, didn't realize, they fried under the lights.