By Graham K. Rogers

In OS X 10.10, Yosemite, System Preferences has seen changes with the design of the interface, while some panels have seen changes, some remain unchanged. The Energy Saver preferences panel appears identical to before although it does have a new icon.

Different Energy Saver preferences panels are displayed depending on the type of computer being used. A desktop computer like the iMac or Mac mini will have a single pane, while a MacBook Pro, with a battery, has a preference pane for each source: battery and power adapter. A feature called Power Nap is available to users of the latest computers and the preference pane has been changed.

On MacBook Pro computers with two graphics cards, there is a checkbox for "Automatic Graphics Switching". The same checkbox is available in the Power Adapter pane. This is to allow the computer to switch automatically between graphics modes for better battery life. For this description of Energy Saver, I am using a 13" MacBook Pro with Retina display (and no graphics switching) and an iMac.

The display information and features differ with the selected power source and with the computer. All, however have the common feature of a single slider for "Turn display off after:" from 1 min to 3 hrs and Never.

Checkboxes are available for controlling how the computer works with the sleep feature, although not all are available on every device.

On the iMac I use, the following are shown:

• Put hard disks to sleep when possible
• Wake for network access
• Start up automatically after a power failure

Energy Saver Preferences on iMac

The last one is not available on the MacBook Pro I use. In earlier versions of OS X, there was a further button marked, "Allow power button to put the computer to sleep." This is no longer available.

In the Battery preferences pane, the MacBook Pro shows two checkbox options as in OS X 10.8, Mountain Lion:

• Put hard disks to sleep when possible
• Slightly dim the display while on battery power
• Enable Power Nap while on battery power (a text below describes what Power Nap is)

When using the Power Adapter the MacBook Pro shows four checkbox options:

• Prevent computer from sleeping when the display is off
• Put hard disks to sleep when possible
• Wake for Wi-Fi network access (a slight change in the text here)
• Enable Power Nap while plugged into a power adapter

Underneath these checkboxes on both panels is information about the current state of the battery charge and the estimated time until full. To the right of this is a button, marked Restore Defaults.

A menu appears when the user clicks on the menubar icon. Items at the top of the menu are: either Time "Until Full" (adapter), or Calculating Time Remaining (battery) or a time figure; followed by "Power source" (battery or power adapter). The Current Battery charge or Time Until Full will be displayed on the Energy Saver preference pane.

Below this is a new section. When first opened, it will display "Collecting Power Usage Information". When the menu is held open, this changes to "Apps Using Significant Energy" and any such applications are listed.

At the bottom of the menu are "Show percentage" and "Open Energy Saver Preferences". When a power adapter is connected to the computer, menu items change and Time Until Full replaces Time Remaining (initially "Calculating time. . ." is shown). If there is a problem with the power source, for example the Mag Safe connector is not fully inserted, the icon may show, Not Charging. Other system information may also appear, depending on the state of the battery.

If the same panel is opened while the Option key is pressed, the condition of the battery will be shown at the top of the menu. This will change from Normal to indicate if the battery needs attention. Long periods with the power adapter attached may affect battery life.

Schedule

A button below is for selection of the action: Sleep, Restart or Shutdown. Days and times can also be specified like in Wake or Start up. If the Startup checkbox is selected, a text appears below: "Scheduled start up will only occur when a power adapter is connected to your Mac." There is no text if the sleep box is checked.

Additional Information

A reader, Jon Austin, makes the valid point that - when playing online games - the checkbox for "Put hard disks to sleep when possible" should not be checked. He uses World of Warcraft as an example. To play this optimally, that box should remain unchecked, plus App Nap should be deselected for that application. The relevant folder should also be excluded from Spotlight searches.

I also found that using a disk with Thunderbolt cable, Finder would periodically report a spontaneous ejection. There is a risk of data loss if this happens. I am fairly certain that this is for the same reason and Put hard disks to sleep when possible should not be checked, but I am also suspicious of Power Nap. Other disks (USB 2, USB 3 and Firewire 800) were not affected.

See Also:

• Accessibility
• App Store
• Bluetooth
• CDs & DVDs
• Date & Time
• Desktop & Screensaver
• Dictation & Speech
• Displays
• Dock
• Extensions
• General
• iCloud
• Internet Accounts
• Mission Control

Graham K. Rogers teaches at the Faculty of Engineering, Mahidol University in Thailand where he is also Assistant Dean. He wrote in the Bangkok Post, Database supplement on IT subjects. For the last seven years of Database he wrote a column on Apple and Macs.