Hey Mike... I went with the PIAA Intense White bulb which is rated at 4100K (kelvin). The higher the # the more blue the light, and the lower the # the more yellow the light. You can look at a kelvin scale
here.
The high/low bulb is called an H4 and is a standard automotive bulb so yeah, it's plug and play. For more money, PIAA has a bulb specifically made for motorcycles in that it is supposed to stand up to vibration. I could see using that one for off road riding but not for our cruisers. I've been running with PIAA for two seasons without a hiccup.
These bulbs make a difference. They use the same 60/55 watts but are rated as 135/125 watts. Kinda makes the old bulb seem like a candle in comparison.
