Stock OEM halogen or incandescent bulbs are typically around 3200 Kelvin, which is a yellow light. High visibility headlight bulbs range from 4000-5000 Kelvin, which is much brighter and whiter, increasing the rider's ability to see what's ahead of them as well as increasing visibility of the driver to oncoming traffic. You'll notice that some bulbs have written as "55=110W". This means that the bulbs technology allows them to get the equivalent of 110Watts of light out of a bulb that only uses 55Watts… energy saver.
Kelvin: Color temperature is a unit of measure for the color of light ? it is not necessarily related to the heat of the light source. A higher color temperature represents a color closer to actual sunlight. H1, H2, H3, and H7 bulbs are usually referred to as such. An H4 bulb is also referred to as a 9003 or an HB2.
I've found some comparison of the Color Temperature, which might be useful for others.