The "4000K" only refers to the color temperature of the light, not its output. Output is rated in lumens, with the highest-powered XML2s have 1420 raw lumens, and the lowest HP48s having 265 lumens. The HP48s have a noticeable output increase versus stock, though you may want to stick with the mid-tier XP80s if you want a good increase in output without being overly bright for other drivers.