The Energy Saver program helps you and your Mac in a number of ways. By blacking out the screen after a period of inactivity, it prolongs the life of your monitor. By putting the Mac to sleep after you’ve stopped using it, it cuts down on electricity costs and pollution. On a laptop, it extends the length of the battery charge by controlling the activity of the hard drive and screen.
Best of all, this pane offers the option to have your computer turn off each night automatically—and turn on again at a specified time in anticipation of your arrival at the desk (Figure 10-15).
Figure 10-15. Top: Here’s what Energy Saver looks like on a laptop. In the “Turn display off after” option, you can specify an independent sleep time for the screen.
The Energy Saver controls are different on a laptop Mac and a desktop Mac. In fact, they differ depending on which laptop or desktop model you have.
Computer sleep. This slider exists only on pre-2013 Macs. (The processors in newer models sleep automatically.) It controls when the Mac will automatically go to sleep—anywhere from 1 minute after your last activity to Never. (Activity can be mouse movement, keyboard action, or Internet data transfer; Energy Saver won’t put your Mac to sleep in the middle of a download.)
At that time, the screen goes dark, the hard drive stops spinning, and your processor chip slows to a crawl. Your Mac is now in sleep mode, using only a fraction of its usual electricity consumption. To wake it up when you return to your desk, press any key. Everything you were working on, including open programs and documents, is still onscreen, exactly as it was.
Turn off display after (or Display sleep): This slider controls when the screen goes black to save power.
Below the sliders, you see a selection of additional power-related options. On a laptop, the two tabs at the top of the dialog box let you create different settings for the two states of life for a laptop: when it’s plugged in (Power Adapter) and when it’s running on battery power (Battery). That’s important, because on a laptop, every drop of battery power counts. Here’s what you may see:
Put hard disks to sleep when possible. This saves even more juice—and noise—by letting your drives stop spinning when not in use. This option appears on both the Battery and Power Adapter tabs, so you can control it independently for each power source.
Slightly dim the display while on battery power. You see this checkbox only on the Battery tab for a laptop. It means “Don’t use full brightness, so I can save power.”
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And when your laptop is plugged in, the sudden dimming of the screen becomes a handy signal that you’ve lost power. Maybe your power cord needs replugging, the power strip went out, or there’s a massive blackout in your half of the country.
Gem in the Rough: Mysteries of the Battery Menulet
If you’ve got a laptop, don’t miss the checkbox in Energy Saver called “Show battery status in the menu bar.” It puts a handy status indicator (
) in the menu bar.Without clicking the menulet, all you see is an icon that represents the battery charge. If you turn on Show Percentage from the menulet’s actual menu, then the menulet can also show how much charge remains, in percentage form.
Here’s what the menulet icon may show:
Lightning bolt in the battery. The laptop is plugged in and the battery is charging or charged.
Superimposed X. The laptop is plugged in, but the battery isn’t in right, is missing, or isn’t getting a charge for some other reason.
Emptying black battery. The laptop is on battery power and has at least 25 percent power left. (The width of the bar reveals how much charge is left.)
Emptying red battery. The laptop is running off of battery power but has less than 25 percent charge remaining.
A nearly invisible red bar means you have less than 9 minutes left. Save those documents, buddy.
If you click the menulet, you see an estimate of actual time remaining on your battery charge, in hours:minutes form. (If the battery is charging, then you see how much time remains until the battery is fully recharged, like this: “0:24 Until Full.”) Either way, the readout is counting down (or up) to that joyous moment.
The menu also offers a terrific list: Apps Using Significant Energy. When your battery is running low, it’s a great way to see which apps are guzzling down your juice.
Finally, if you Option-click the menulet, you get a health report for your battery. It might say, for example, “Condition: Normal.” When the battery needs your attention—when it says “Service Battery,” “Replace Soon,” “Replace Now,” or “Check Battery,” you don’t have to press Option. You’ll see that message every time you open the menulet.
Wake for Wi-Fi network access. This option (on the Power Adapter tab) lets you access a sleeping Mac from across the network. How is that possible? See the box below.
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The wording of this option reflects how your Mac can connect to a network. If it can connect either over an Ethernet cable or a wireless hotspot, it says “Wake for network access.” If it’s not a wireless Mac, you’ll see “Wake for Ethernet network access.” If it’s a MacBook without an Ethernet adapter, it says “Wake for Wi-Fi network access.” On a laptop, the “wake” feature is available only when the machine’s lid is left open and you’re plugged into a power outlet.
Enable Power Nap. Power Nap is an ingenious and extremely useful feature for laptops—specifically, flash-storage laptop models that were introduced in 2012 or later. (On older laptops, it doesn’t appear at all.)
Anyway, when you turn on Enable Power Nap, the Mac keeps updating Internet data even while it’s closed and asleep. About once every hour, it wakes itself—without activating any fans or lights—long enough to check for mail, calendar updates, Photo Stream updates, software updates, and so on. When you wake the laptop later, you’ll be delighted to find that it’s completely up to date, with new email waiting and all your iCloud programs (Notes, Messages, Reminders, and so on) up to date. And the lid was closed the whole time!
Power Nap comes set to work only when your laptop is plugged into a power outlet, but you can make it work on battery power, too (Apple says the battery hit is very slight). You’ll find separate on/off switches on each of the Energy Saver tabs. On the Battery tab, it says “Enable Power Nap while on battery power”; on the Power Adapter tab, it says “Enable Power Nap while plugged into a power adapter.”
Most of those network functions take place even when the laptop is on battery power. But when it’s plugged in, Power Nap also performs two more time-consuming functions: Time Machine backups and App Store software updates.
Of course, Power Nap means that your laptop isn’t quite as somnolent as it used to be while the lid was closed—it’s using a little more power.
Start up automatically after a power failure. This checkbox appears only on desktop Macs. It’s handy if you leave your Mac unattended and access it remotely, or if you use it as a network file server or web server. It ensures that, if your lonely Mac seizes up or crashes, it will start itself right back up again.
Up to Speed: Where Your Free Hour of Battery Life Came From
Some of the features Apple works hardest on are things you’ll never even see.
One big category: technologies designed to save battery power. Since 75 percent of new Macs are laptops, battery life is a big, big deal.
Here are some of these behind-the-scenes juice-preservation techniques in recent Mac versions, bearing the names Apple has given them:
App Nap. When a program’s window is completely covered up by other windows, the Mac slows down that background app. (Ditto for Safari background tabs.) Slower means less power-hungry—as much as 23 percent, Apple says. (If the app is doing something in the background, like downloading or playing music, then App Nap doesn’t kick in.) The instant you bring the program to the foreground, it snaps back to full speed.
iTunes HD Playback Efficiency. By reducing the frequency of hard-drive access during iTunes video and audio playback, Apple says the Mac uses up to 35 percent less energy.
Timer Coalescing. MacOS attempts to consolidate processing tasks and feed them to your Intel chip in bursts. That way, the processor earns tiny micro-vacations—idle time. More idle time means less power use. Your savings this time: as much as 72 percent.
Safari Power Saver. Flash videos and animations are notorious battery hogs. So when Safari spots a Flash video off at the edges of a web page—on the side or the top, for example—it concludes that what you’ve got here is an ad. And it stops the ad from playing until you click it. (You see a banner on the video that says “Safari Power Saver. Click to start Flash Plug-In.”)
Apple says all of its power-saving features together can extend a MacBook Pro’s battery charge by as much as an hour. Not bad for a free system-software upgrade, eh?
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If you’ve also turned off (or left off) Ask to Keep Changes When Closing Documents and Close Windows When Quitting an App in System Preferences→General, then your Mac will both restart and restore everything you were doing. You may, in fact, never even realize that a crash or freeze occurred while you were away! (The telltale sign: Any web pages you had logged into, like a banking website, will have logged you out.)
Show battery status in menu bar. This on/off switch (laptops only) controls the battery menulet described in Checkbox Options.
By clicking Schedule, you can set up the Mac to shut itself down and turn itself back on automatically (Figure 10-15, bottom).
If you work from 9 to 5, for example, you can set the office Mac to turn itself on at 8:45 a.m. and shut itself down at 5:30 p.m.—an arrangement that conserves electricity, saves money, and reduces pollution but doesn’t inconvenience you in the least. In fact, you may come to forget that you’ve set up the Mac this way, since you’ll never actually see it turn itself off.