Could you help me explain car lights go on but wont start?

I think most problem of car lights go on but wont start shall be from battery.

If battery is gone, car lights always go on but wont start.

If you have different idea about car lights go on but wont start, please inform me.

My factory is an OEM supplier for all kinds of car lights.

Most of our car lights are all top quality with CE, EMARKS, DOT and ISO9001.

Meanwhile, all of our car lights are given at least 1 year warranty guaranteed.