dim additional light on new loop?

I had a ceiling rose that was wired with a junction box wiring system to the switch (all the lights in the house seem to be wired this way). From that rose I have wired in a loop to another light in my hallway. I have used 2.5 two and core. The circuit works and both lights come on when turned on. However both lights are now dim (previously the original one shone with normal brightness). I assume this is because I am splitting the original power over 2 bulbs instead of just one bulb - is there any way to fix this to get both bulbs reasonably bright?
I have tried reducing the wattage of the bulbs however when both are the same watts they shine dimly, and if one is lower than the other then the lowest wattage bulb shines almost normally while the other barely lights up.
Is there any way to fix this - or will I just have to remove the loop in?
- Thanks