Can Anyone Help Me Parse A Times Clue Please

[Callyandy]

Clue = "Cooler sort of house, where shades may close on boy". Answer = "prison". I get that "cooler" = prison but not the rest. Probably being dense as usual but any help appreciated. The clue is from a Times cryptic crossword book.

[Chinajan]

Unsure, but possibly related to:

PRI - https://en.wikipedia.org/wiki/Photochemical_Reflectance_Index

+ son

[Callyandy]

Thank you Chinajan - will keep thinking

[TheFrogman]

The following lines come from Wordsworth's 'Ode: Intimations of Immortality'

Shades of the prison-house begin to close
Upon the growing Boy,
But he beholds the light, and whence it flows,
He sees it in his joy;

[Callyandy]

Perfect - many thanks to The Frogman. Just shows my lack of knowledge re: Wordsworth. As ever, I'll enjoy finding out more.....