Sleep onset latency
In sleep science, sleep onset latency (SOL) is the length of time that it takes to accomplish the transition from full wakefulness to sleep, normally to the lightest of the non-REM sleep stages. == Sleep latency studies == Pioneering Stanford University sleep researcher William C. Dement reports the early development of the concept, and of the first test for it, the Multiple Sleep Latency Test (MSLT), in his book The Promise of Sleep.