Leaves with black on them on the top of the plant?.

I have a 4 week into flowering, deadhead plant that has leaves turning black on top. I have them under a 400 w hps about 10 inches away and also in the sun during the day. Please look at this and tell me what you think?

Anyone have any ideas?

Cant really see shit in that picture

Sorry, but the 4 leaves or so on the left side are turning black from the tips inward. I tried to take the pic where everything was lit up the same from the sun

Hmmm phos def maybe.

Need more info, soil, nutes, temps, rh etc

Thank you for responding.. It's in fox farm soil and I've been using general hydro.floraMicro and florabloom at just under recommended amt.for feeding every other watering. I use tap water and have been using ph down from mad farmer to keep ph at 6.5 to 7, after I found out my tap water was like 7.5-8 and this was a couple weeks ago. My temps have been 65-78 and humidity at 45 at night and during the day 30-65 as I put them outside in the sun and breeze. They did touch the hps bulb for a min when I was moving them outside...could it be light burn? The leaves are super soft feeling where they are black.

I suspected, it's light burn.

Sorry earlier I was looking at the top of the bud. But now I see the leaf I say it looks like phosphorus deficiency. Probably not light burn IMO.