Don't do drugs, it's stupid. Your idea probably won't work. A lot of people leave a porch on outside their homes at night, not because they're looking to score drugs.
I am not sure what you are asking here. If you mean that leaving lights on will deter people from selling drugs in your neighborhood than I would have to say no. They will just go to a darker part of the street.
A porch light left on does not specifically deter criminals unless it eliminates shadows a criminal could hide in while breaking into your home. These lights are left on by accident so much that it no longer suggests the home is occupied. Instead, have a timer so that lights go on and off inside the house to imply occupancy.
the only thing thats going to come of you leaving your porch light on for drugs, is that your house has become more noticeable by the police that patrol your neighborhood. Unless all the other neighbors houses have their lights on i wouldn't advise you to do that. try putting out some kind of lawn ornament instead.
It could help, but if you want to stop a heroin user, they cannot find their veins with blue lights, which might not be very attractive as porch lights