Such radiation calls for some use of parasols (5)
I believe the answer is:
solar
'such radiation' is the definition.
'solar' can be an answer for 'radiation' (solar radiation is a kind of radiation). I'm unsure of the 'such' bit.
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for solar that I've seen before include "Concerning the sun" , "Of or derived from the sun" , "Mediaeval chamber" , "Relating to the sun" , "like a star" .)