This is a 4 x 6 inch array of 18 LEDs. Very bright. Easily seen in daylight. 1 mile visibility at night. $40 from Harris Cyclery. I bought two Saturday morning and someone else had gotten one just before me. These are really impressive lights, brighter than my home-brew 10W. Because of their larger surface area, I think they will be even more effective in fog. Powered by 4 AA batteries, 60 hrs in blinking mode. Only real problem is that they are so big if you don't raise your seat much it is hard to find a place to put them.