I like to keep an eye on power consumption of anything that is left 'on', especially now the warmer weather is here, in summertime the resulting energy goes to waste. My iMac is meant to sleep when idle, but there is no indicator light to tell you whether it really is asleep or not. And there have been times in the past when I have caught it 'failing' to sleep, thus consuming excess energy, that much is true and seems to be a common criticism of some Macs - and in fairness, most other OS's too.
So yesterday, I plugged it in via a 'power monitor' plug adapter block. Powered up, screen on, but idle, it hovered around 50W, which impressed me as it seemed quite low. When supposedly asleep, it drew exactly the same, about 50W. So my suspicions were right, it was failing to sleep? I spent hours and hours becoming expert on methods of diagnosing 'sleep' problems. Just couldn't fathom it out, the 'pmset' logs all suggested it has slept, the timestamp on the 'sleepimage' file was consistent, yet consumption never varied from about 50W.
Only after more time and effort than I care to admit, working out why it always drew 50W regardless of sleep state, and lying awake myself worrying about it, a final brainwave occurred during the night. I looked more closely at the power monitor. It was set to display 'Hz'.
