Please help what is wrong with my light

I've been battling this problem for almost amonth now. Ive tried everything I can think of, soil, watering, temperature etc...The plants are getting worse by the day and most are dying. I'm thinking somethings wrong with my light. The spectrum is orange so I'm sure it's hps, it's a hydropharm light.

The thing is that I started my first grow with a 150watt hps security light, and everything was fine-in fact the plants were doing amazing. The plants began to yellow as soon as I put the 600watt light on them. What could cause this? I'm thinking about getting a new bulb...

How close is the HPS to your plants? I would start it a bit higher than the 150 and slowly lower it until the plants are used to it.

It's like going from a warm day to a walk on the sun! (well, not that bad - but you get the idea)

This may not even be the problem, but give some input :D

Where are the plants yellowing, do you have pics, what's your PH, how many plants, what strain, info info info!

Yeah, more info is required, it may not even be the light, or it may be a cheap bulb... Tbh, it could be many things..

I don't have a ph tester, do they sell them at home depot? It's just bag seed right now, 2 have become deformed and had to be thrown out. The light is about 2.5 feet away, I moved it up thinking that could be the problem. The leaves aren't really yellowing as much but they are turning brown and black then falling off.

do you have a pic