Resistors?

Hi,
I am about to build an LED stop/tail light for my bike using LEDs
I have seen where to buy pre-wired LEDs for 12v systems which I suppose is the easy way.
My question is this;
If I wire 120 LEDs into a panel for the backlight how can I get them to be brighter when the brake is pressed?
The unit will have three wires going to it. One live, one negative, and one that's only live when the brake switch is activated.
Would it work if I connected the live wire to the LED panel via a resistor, and connected the brake switch live to the LED panel by-passing the resistor?
If so what resistor and how many?
If that isn't the way to do it, could someone please point me in the right direction?

Thanks in advance

 

Thanks for the advice.
I will do 60 LEDs as normal, then the other 60 when the brake is activated.
I wasn't sure, but had to ask.
Thanks for your time