What vehicle?
There are lots of options on lights.
The actual light unit and lens can make a difference. So bear this mind.
Getting a good 12+v at the bulb will offer the most performance. There will be resistance in the factory loom. You don't really need to do anything special, all you are doing is converting the headlights to run through a relay, using the existing wiring to activate the relay. Same as you would when fitting spot lights.
Higher wattage bulbs are an option, although less common these days. 80/100w should be fine. Think I've run 90/130w years ago. Might also find some 80/120w too, haven't looked for ages. High wattage bulbs will be hotter out the front and draw more current.
However there are lots of 55/60w bulbs that offer higher outputs. These seem a sensible option these days. Although some have a blue tint on the bulb which I'm personally less keen on. Such as the Osram Nightbreakers:
www.osram.com
I found the colour temp changed from dip to mainbeam, which really irritated me and mainbeam while bright just wasn't a very nice tint for country driving, making the greens and browns all appear a bit more grey'ish.
I prefer their silver line as the tint is nicer and more consistent:
www.osram.com
If you want to move away from halogen there are some options.
In theory it is not legal to run LED or Xenon bulbs in your headlights. You could fit new LED units or Xenon ones, but they would need to be approved, you'd also need headlight washers and some kind of auto self levelling facility.
However if you are comfortable with running LED or Xenon bulbs it does open up options. Xenon is less obvious for the most part and does offer a lovely tint that is right around 4300-5000k. Arguably the nicest light of any headlight source. Xenon does need to warm up when you first turn them on, but a good option otherwise. Biggest issue is buying a quality set. Ebay is littered with naff rubbish that usually turns out to be very blue light. But shop about and there are some nice Xenon sets.
LED is also an issue. 99% of the bulbs on the market are a high Kelvin rating which offers shocking ice white or blue light. This has poor colour rendition and also induces eye strain. So you really need to research to make sure you get a good LED bulb. It is also a bit of trial and error as some LED bulbs cause a terrible profile. It will also vary based on what lamp units you have too.
So it will be trial and error, buy some, fit them. Then check to see if the beam profile is ok or not. If not, you'll need to send them back and try some others. LED bulbs are also very obvious due to the colour of the beam. So you may get pulled come MoT time.
There are some warm white LED options, but these may not out perform a good halogen setup by much.
NEW UPGRADED MODEL, MORE COMPACT, EASIER FIT, SAME PERFORMANCE This is a pair of top quality, H4 LED headlights made with the latest high power SMDs which produce a clean focused light with no glare and a very well defined beam that replicates the low and main beam pattern of a standard H4...
www.classiccarleds.co.uk
