Both versions have the same total output. The only difference is in the focus. If riding mostly in urban conditions consider the "R" or near-field version (40 lux). It will light up the road immediately in front of the bike. If you're riding fast down hills or charging your twisty bike trail, consider the "N" version (60 lux). It will focus all the light further down the road.
Light is provided by a high power LED so no bulb replacement should ever be needed. The LED should last many thousands of hours. The LED will come to full power at slower speeds (<5mph) and be brighter than a halogen.
Both models have Busch and Muller's "Standlight" feature. Standlight is a condenser that is charged while riding so that when the bike comes to stop the light will stay on for several minutes. Standlight uses no batteries and requires no maintenance.
Lumotec IQ Cyo T (tightly focused beam)
Lumotec IQ Cyo RT (taller beam)