Why do aircraft have to dim the cabin lights when landing ?

Under normal approach and landing conditions cabin lights are dimmed several minutes prior to landing to allow time for pupil's of passenger's and cabin attendant's eyes to sufficiently adjust (dilate) to a darkened environment so that cabin occupants would have an adequate level of acclimated night vision during an emergency situation that might require location of emergency exits, slide evacuation and subsequent foot navigation on the ground.... all of which would occur in a darkened (and possibly smoke obscured)environment.

Of particular safety concern is the importance that passengers be able to locate and follow the low light level cabin floor lighting strips leading to emergency exits as well as other low level lighted emergency exit signs and cabin attendant flashlights... all of which could be partially obscured by smoke, dust or debris in event of a high impact landing. In this situation the eyes need all the "light gathering" ability they possess....and that can only happen if cabin occupants eyes have been "pre-conditioned" for night vision in a darkened environment prior to landing.

Could be wrong but someone told me it was so our eyes become accustomed to the dark just in case there was a crash. That way when the lights go out on hitting the ground we have a better chance of finding the way out. Sounded plausible to me!

so nobody outside can see all the asians flying in.

Actually, when I was working as a flight attendant, I heard a different reason. The initial reason is still the same (get accustomed to darkness), but the rest deals with security purposes.

The crew needs to be able to see better fire or smoke outside of the airplane during landing or evacuation.