wiring a new light and switch, connect to existing fitting

[simey78]

Hi, Im looking to install a new light fitting with its own new light switch. I read your info about connecting the switch to the light fitting then running wires to an existing ceiling rose, an existing junction box or new junction box. The easiest option for me would be connecting to an existing ceiling fitting in the house as they are easy to access and I am familiar with the wiring. My concern is that if I was to loop into an existing light, would my new light only work when the existing light is in the on position? In other words, will the existing ceiling rose always be able to supply power to the new light whether the existing one is in the on or off position? If this will be a problem, how can I get around this? Thanks.