H4 vs. H5
 

I have a 1987 3.2 Carrera with H5's. If I switch to H4's will I get any improvement in lighting? What are the basic structural and performance differences between the two lights?
Thanks Mark

Just clean the inside of the H5's. You will be pleasantly surprised. I added Hella 450's in the stock fog holes, and I can't outrun the light.

H5's have the 3 DOT alignment bumps, AND (as you know) get cloudy quickly.

The H5's fitted to my car when I bought it had no bias to the cut-off at all. In fact, I moved the car from one country to another (with an opposing traffic pattern) and never changed the lights. Never got an irritated flash once, and drove on country roads a lot.

I switched to H4's (from Pelican, with US lenses) and fitted the appropriate lens for the country. I found that they're comparable in brightness/light output (H4's are slightly brighter for me, but that might just be newer reflectors).

However, I find the beam pattern on the H4's is far superior - it illuminates the kerb and nearside of the road very well on dipped, with a sharp cutoff - and just throws light straight down the road on main beam. I'm running stock bulbs in the H4's and was in the H5's as well.

Strictly speaking though, H4's aren't legal in the US, as they don't have the DOT nubs or marks - E-coded doesn't count for anything to the DOT, who didn't approve H4's until the early 90's or so, despite millions being used everywhere else in the world since their introduction in the 70's.

In fact, according to Dan Stern's website, until comparatively recently, the DOT regs required some %-age of beam scatter straight up on dip beam "to read road signs".

Unfortunately, the FAQ contains a lot of the most detailed information, and its been down forever..

http://www.danielsternlighting.com/