got 250kw son pt light help

just got a 250watt high presure sodiem light and my plants are 3 weeks old can someone tell me how many hrs light they need please
and when do i start feeding them plant food

They should be getting 24 hours of continuous light. They are 3 1/2 feet tall and you aren't feeding them yet!!? What light cycle have you had them on? You need to buy a book if you don't know simple grow techniques

sorry misread the post. Not 3 feet tall. But three weeks. You should be giving them a nitrogen rich fertilizer by now

whats the best fertilizer to use and how close should the light be to them

That depends on the light and how hot it is. As close as you can get it, without burning the plant is good if it is a hot bulb. Go with organic fertilizers such as manure, guano, fish emulsion, compost, seaweed. Make sure that the fertilizer you are using is high in Nitrogen for the vegetation phase and high in Phosphorus and Potassium for the flowering phase. Also a good floir feeding spray mix is great as well, because it will give the plant a lot of trace elements and minerals that are not provided with regular fertilizers and plants can absorb nutrients from the leaves faster than they are absorbed and distributed from the roots.

Oh and use half the recommended fertilizer strength, less is not bad for the plant, but more can kill it or screw it up

Rule of thumb to go by when it comes to your light and its distance from the plants is to check the temperature with your hand. If it's hot on your hand, it's definitely hot on the plant. As for vegetation light times, I've always used 18 hrs of light to do so, but I'm not saying I'm an expert, either. I just remember a site saying that darkness allows the plant to develop roots and roots are important. At about a month or to your desired height, you can switch to flower power 12/12 lighting. I hope this helps.

right will do thanks for ur help