I turn bathroom switch on lights takes a long time to come on what is wrong

Please define what you mean by " a long time to come on" - do you mean a few seconds? Or minutes?

Also, what kind of light is it? Is it fluorescent (the kind of light fixture with a long skinny lamp), or is it a compact fluoresent light (CFL) - which are often used these days in place of a standard incandescant bulb? CFLs can take a couple of seconds to come on, and then a minute or two to warm up to full brightness.