Why? Is it lightstress? LED Spider Farmer 480 Watt...

Burning from feeding too much or too often ........or both. It is not a deficiency, it is over feeding, plain and simple. The super green, plastic looking leaves is classic over feeding symptoms. "Light stress" will not cause burnt leaf tips.

the tacoing around edges might be climate-related. several things cause, bot deficiency and toxicity, burnt tips, so more info needed to eliminate possibilities. any old leaf symptom chart can help there. light damage usually involves interveinal damage and droopy plants after hours of exposure. This looks more like an issue related to balance of nutrients provided. 480w light is probably good for just under 16 sq ft. over 18h probably only need 67% power and 100% power over 12 hours. Algebra can determine if yout 60% is close enough or not. over 18h you only need about 54 umol/s of PAR average across canopy. 80umol/s PAr for 12 hour operation. That's ~861 PPFD for 12h if i recall and 67% offthat for 18h. The proportional differences relative to hours of operation are not coincidental. take your light's spec sheet and do a little math if you want to set you rmind at ease.

could be beginning of K deficiency, also P next time do more pics for more accurate diagnose

It is burning a little bit but not necessary from light alone. Take into consideration also relative humidity, temp and air flow. Too much or too little of that can also affect the plant this way. Yet again, no need to worry. Just lover the intensity a little bit or distance your light a little bit more from the canopy and you'll be fine. Good luck!