Leaves are dying

Is it light burn?

Probably not light related. The middle photo looks like some type of toxicity or perhaps signs of alkaline soil(ph is too high). The outer photos, the light is hard to see true color, and they're pretty far gone already to know with any certainty. If it were light burn, the leaves closest to the top would be in the worst shape, buds bleach (if temps are ok).

Def. not light burn, with that the outer fringes of your leaves become dried and yellow/brown. I'd say make sure your PH level is comfortably between 6.0 and 6.5. Have you been adding any nutrients to your soil? If so, what kind/how much? Are you watering daily?

Here is a good example of light burn, middle right of my big plant. It's not on top because the burn happened about a month before I took that picture, when I only had CFLs to grow with. I would say you have a watering or nutrient problem, and PH falls under nutrient problems because an improper PH can block the roots from pulling out all the required nutrients.

I'm doing hydro, should I add only water not add any nutrients for a week to the reservoir or so to see if anything change? The amount of nutrient I add is a controlled amount and nothing like this have happened before.

Personally I wouldnt pull nutes using hydro, at least not yet, as that could be a further detriment to it's condition... could just as well be a deficiency, from what I can see.

Based on the chart tropicalcannibas patient found (thank you, tropicalcannibaspatient) it may be mobile or immobile nutrients possibly? Do you have a decent water pump and an oscillating fan on them? If not those probably arent bad ideas to start with. The partial yellowing on the one leaf may be due to a slight iron deficiency? Hard to say anything for sure. If you weren't using hydro I may have guessed overwatering/lack of water drain. Lol

Are you testing your PH? If so, what has it been reading?

How many of your leaves have died recently? Actually, it looks like many of your other leaves are doing pretty well. How long have you been flowering? If you're toward the end of flower and only a few leaves are dying that's fairly normal, probably just the plant putting most of it's energy into the buds and so forth.