Hello there!
You're saying that you've replaced the headlamps with new halogen units. Not a bad idea in itself, because Joe Lucas was (still is!) known as "The Prince of Darkness"

. Hehehe. However, you might like to think about the following:
Wattage
However, the wattage will make a difference to the brightness. The old sealed-beam units on my Morris were rated at 50w40 or something like that, with 50watts being the main and 40watts being the diped beam.
The dynamo can cope with 60w55, as fitted to Phyllis. Anything more than that, and it hasn't got a cat's chance in Hell, I'm afraid. It just won't produce enough electricity to power them to a decent brightness.
Aside from that, those lovely 130w100 units I've seen for sale
really need relays and
MUCH better wiring!!
For full brightness of the 60w55 lamps, and to fit accessories like foglamps and a decent stereo, I fitted an alternator.
Alignment
I don't know how you checked the brightness of your lights (I hope it wasn't by looking straight at them...

!!), but have you thought that they might be misaligned? Apparently this can make a fair bit of difference.
Failing that, it's probably a dodgy earth to the lights, or indeed anywhere in the loom, most likely.
Anyway, get it sorted and you might even be able to use your Moggy at night

.
