Well first this is a open ended question. You need to get an education on performance lighting.
There are five main styles of lights. One light is not going to do it all.
Pensil beam: LONG distance narrow beam. Good for high speed running. The problem is they are so focused that unless the light is dirrectly pointed at something your not going to see it. For a 4x4 it's a waste. If it points at a hill then all you see is the hill in a very small area. These are for distance and vehicles running 50-100mph. These are almost always run with a second set of lights in racing. The beam is so focused you only see what is directly infront of you. It will hardly light up the next lane or the side of the road. These are for LONG straight roads at speed.
Euro beam: Good distance but a wider beam. Good for use on long streches of hwy or desert running. Will blow any head light highbeam away. Not as focused so it will light up a 4 lane road pretty good where a pencil is only going to light the lane your in. Guranteed to dim auto dim headlights at about a mile away.
Flood/cornering: This is a good light for a 4x4 on tight twisty, hilly trails. Lots of light in a wide area including up so if your approching a hill you will light it up better. Not a lot of distance but more then enough for typical trails.
Driving/city: this is a light that can be used in addition to a low beam. these are ment to mount low to light a wide flat area. Helps with cornering and lighting objects on the side of the road It can throw a beam as far as a stock high beam but the low mounting location causes ground objects to prevent a lot of travel.
mounted high and straight out it does good for twisty trails without a lot of hills. Don't want to use with the low beams on the road if these are mounted high. The wide pattern would run people off the road. This is the tyipical light you would see in the parts stores. Hella 550's etc.
I run a set of Bosch driving (the same ones you would see on volvo white semi's) on my truck and they do a pretty good job on the trail mounted headlight high. The flat beam is not so bad on the guy's in front of you unless it catches on of their mirrors. I had them so I used them. I would have gone for a flood if I were buying but the flood would have been more bothersome to people you follow so would have to be more carful about when they are on.
These work pretty good when mounted low for fog. The flat pattern undercuts the fog and doesn't glare back at you so bad. It is esentially the same pattern as a "Fog" but with more distance and white. The yellow "fog" lenses tend not to glare as bad in the fog but they cut down the distance as well.
Fog: Low flat patten usualy with a colored lens. They are ment to be mounted low to help prevent glare off the fog. The distance is trimmed down to help with this. Fog basicly bounces the light everywhere. while withought fog these would not light very far ahead the refraction of light caused by fog would let you see better since it's not reflecting back. Fog is water vapor and it acts like billions of little mirrors and redirects the light aimed into it. The goal is to aim the light in such a way that it's not coming back. More power is worse in the fog.
There are also replacement head lights available. I run a set of Hella H4 Rallye headlights in my Supra. The low beam doesn't bother oncoming drivers but the Highbeam is like a Eurobeam and much better then the conventional head lights in both Low and high. I have the not so legal varity but they do sell a set with a trimmed down highbeam that are legal.
Now there are new light technologys out with more candle power bulbs. This includes HID and Xenon. Really same patterns just a brighter bulb. Also costs a lot more. A set of conventional Ralley 4,000 Euro beams will set you back about $240. A seto of HID Rallye 4,000 are close to $1,000.
I like Hella. I have a seto of Rallye 1,000 Euro beams that I will be putting on my Burb and wire them to work with the high beams. They would be a waste on my 4x4 and due to their size and the over grown trails I deal with I would likely destroy them. I also run with groups of trucks when off road and unless I was the lead truck I would not be able to run them.
These are great mounted up high but most states it is not legal to run a light above the headlights on the hwy. They are supose to be covered when on the hwy. On a Burb at headlight level they will be legal and usefull.
When you see a desert race truck, FIA Rallye car etc with a bunch of HUGE lights it's usualy a combination of patterns. They will have a set of floods for the tiwsties and either a seto of pencil or euro beams depending on the course and speeds. Sometimes they will run all three.
Here is a good section at Hella's site that explains all the beam patterns plus some special combination beam patterns. Nice illistrations.
Hella Rallye 4,000's
Hella's main US site
www.hellausa.com
