All classic K bikes utilize a 60/55 watt dual beam (high/low) H4 halogen headlight bulb. Though halogen bulbs were a giant leap forward when they started appearing in cars in the 70s, they are now ancient technology, like connecting to a network via a dial-up modem. If you're still running the factory bulb then it's a good idea to replace it with something newer and better. Throw the old one away or stash it in your tail cowl as a back-up spare.
In order to get more voltage to the headlight (which equals more light) and prolong the life of your headlight high/low beam switch on the clutch perch it is strongly recommended that you add headlight relays to your K bike. It's fairly easy to do even if you're not an electronics whiz as there are plug-n-play kits available.
Click here to visit the headlight relay topic.Here's my experience and opinions on various headlight bulb options.
Osram 64193: This is a nice fairly bright white 60/55W H4 bulb. This is a pretty decent quality and affordable bulb. They can be had on Fleabay for pretty good prices.
CATZ brand H4 Bulbs: These are quality bulbs made in Japan available from Fleabay vendor jcatz872 and, though a little on the spendy side, are good quality bulbs that put out a lot of light. Personally I'd go for the 3900K white ones.
PIAA: PIAA is a well-known high-end vehicle lighting manufacturer. They have a variety of H4 bulbs available. They do make good lighting products but they are definitely on the spendy side of the spectrum. Best prices can probably be found on Fleabay. Link to PIAA site:
http://www.shopatron.com/home/search/353.0.1.1?q=h4&t=product&cf=10545.0.0.0.0Generic "Xenon" bulbs from Fleabay: These bulbs use xenon gas which burns brighter and whiter than halogen. You can get them for less than $10/pair on Fleabay. (Sometimes they are listed as "HID" but they are not. You simply cannot buy a set of HID bulbs and ballasts for <$10 shipped.) The 60/55W ones are definitely better than your old stock halogen bulbs. Once you've added relays and beefier wiring you can also buy higher wattage versions of these. For example: 100/55W, 100/90W, 130/90W, etc... These are what I usually run and am happy with. (
DO NOT run higher wattage bulbs without adding relays and beefing up the headlight wiring. Otherwise you will most likely melt the insulation off of your headlight wires and cause a short or maybe even a fire since the factory headlight wiring is not fused.)
NOTE: Anything with higher wattage than 60/55W is not DOT-compliant and therefore technically illegal. However, if you keep the cutoff at the top of your low beam properly aimed not to the blind the car ahead of you in their mirrors or blind oncoming traffic you probably won't be hassled by law enforcement. I've been running higher wattage bulbs for tens of thousands of miles for many years in many states without being hassled.
That's my .02. If anyone else wants to share their opinions on these or different H4 headlight bulbs then feel free to add to this thread.
H4 Handling: When handling headlight bulbs do not touch the bulb glass with your fingers. Oils from your skin (your fingerprint) are left on the glass. Headlight bulbs get pretty hot and cook that which will greatly shorten the life of the bulb. If you do accidentally touch a bulb with your fingers then clean it off with some rubbing alcohol and a clean rag or paper towel prior to installation.
