Hi fellers this may seem like a daft question but, Why will the bike not start with the lights on but won't with them on.It turns over no problem, but won't fire,turn the lights off and it starts first press.

Insufficient voltage at TCI unit.?
Requires in excess of 9.75v to spark.
Presume starter plus headlamps reducing voltage below this.
Could try it with an auxiliary battery jumpered to bike so as to confirm.

Your battery's low on charge and with the lights on it takes away just enough that the bike doesn't spin over quick enoungh.

Check the battery with a volt meter, you should get 13-14v with the engine off. If the bike's stored outside it can be the battery gets cold which won't help it.
It could help to have the carbs set up, if the mixture is a bit off it won't help.
The spark plugs could be a bit past their best, new plugs always help.

The next thing is cheap :) how do you start the bike from cold ? turn the ignition on and let the fuel pump click until it stops (you might need to flick the kill switch to make sure. Choke open wide no throttle, then start it.
But if it won't start with the lights on .... turn them off, I always do as a matter of course.

the battery is only 4 months old & is a ytx9-bs so not cheap &is stored in a garage over night,so could there be a drain on the battery or could it be the ignition unit itself.

The TCI either works or it doesn't. No inbetweens but it must have sufficient voltage to fire the spark.

Clean the carbs and change the spark plugs

cheers,bike started first prod this morning but will get plugs ect although they were changed when i stripped and cleaned the carbs 6 months ago.Bye the way how do i become a site supporter.

Of the plugs are 6 months old you don't need to replace them.

If it started ok this time, is there anything you did that was different ? best to do it again