Superficial brightness observed outside hospital (5)
I believe the answer is:
sheen
'superficial brightness' is the definition.
(I've seen this before)
'observed outside hospital' is the wordplay.
'observed' becomes 'seen' (synonyms).
'outside' indicates putting letters inside.
'hospital' becomes 'h' (abbreviation for hospital on maps).
'seen' going around 'h' is 'SHEEN'.
(Other definitions for sheen that I've seen before include "Soft lustre on a surface" , "Surface gloss" , "Glow" , "Sureface shine" , "Radiance" .)