Density dependence of SOL power width in ASDEX upgrade L-Mode

•The power spreading in the divertor region is described by the competition of perpendicular heat diffusion and parallel electron conduction.•The in/out asymmetry of the power fall-off length λq is studied for a closed divertor configuration in hydrogen, deuterium and helium.•A strong density dependence of λq,i on the inner divertor target with density is observed.•An interpretation of the observed dependencies of λq using a drift based model is given.