soporific

/ˌsɑːpəˈrɪfɪk/

sop·or·if·ic

BrE /ˌsɒpəˈrɪfɪk/

NAmE /ˌsɑːpəˈrɪfɪk/

(formal)

making you want to go to sleep

the soporific effect of the sun