Begin to understand how to date rays from the sun? (3,8)

I believe the answer is:
see daylight
'begin to understand' is the definition.
(I've seen this before)
'to date rays from the sun?' is the wordplay.
'to date' becomes 'see' ('see' can be a synonym of 'date').
'rays from the sun?' becomes 'daylight' (I can't explain this - if you can you should believe this answer much more).
'see'+'daylight'='SEE DAYLIGHT'
'how' is the link.
Can you help me to learn more?
(Other definitions for see daylight that I've seen before include "what 14 [FATHER CHRISTMAS] won't be able to do if he's at home today?" , "what Lapps can't do at Christmas" , "Begin to understand" .)
