Sunday, June 09, 2013

How much power does a laptop use?

More accurately: how much power does MY laptop, as configured, use?

Laptop Virgin

Let me be honest: I did not get my first laptop until a few years ago after I graduated from university. There just wasn't ever a need for a portable computer and they were still growing in popularity during my time in school -- I'm not that old. Don't get me wrong, I've had a computer for a long time, but in the form of a desktop.

This matters because that means my experience with laptops is somewhat limited. However, I do know that they've been getting more power efficient over the years with longer lasting batteries. And they've gotten way smaller.

A Snapshot of Laptops and Usage Patterns

The important takeaway is that my laptop isn't representative of all laptops out there. My machine is was one of the cheapest units available in late 2010 when I decided to get a laptop for graduate school. This probably means that the components were relatively "weak" compared to top of the line equipment. Weaker equipment generally means less power required -- assuming it's from roughly the same generation of electronics because things are getting more efficient (i.e. less does more).

Now that we've covered hardware, let's do software. The more stuff one has running and loaded into the background, the more power is generally required to run things. For example, laptops go into standby/hibernate to conserve power by not doing much of anything when no one's at the helm. How much stuff you have loaded and running, even when you're idling (i.e. doing nothing), makes a huge difference.

Laptop Power Consumption Demonstration

On a boring weekend evening (does 12am count?), I decided to hook my one and only laptop up to a Belkin Conserve Insight Energy-Use Monitor to see how power consumption varies depending on the activity. I have tested this device with light bulbs before and it looked accurate. Also, I only have CFL and LED bulbs in the house nowadays, so the power reading was in the <10W range. Let's just assume that it's accurate?  But electricity isn't that simple and the meter's never been calibrated or tested carefully.

Walkthrough of Old Video
Important note: Sorry, took the video town because the quality plain sucked -- it was like my second ever. I'll make a new one when I get a chance with better lighting. The video has been sped up x4 because I'm usually too lazy to watch long videos, so I assumed the same of you. I had 15 minutes of footage, so be thankful! And sorry for the horrible lighting.


Starting from the off position with just the A/C cable and power block plugged in, the power use is pretty low. The reading may not be closer to zero because I hadn't used the laptop in a while, and the battery is probably topping off the charge.


The machine is turned on and the power use spikes to almost 40W, then settles closer to 30W.


As you may know, Windows usually isn't finished loading stuff and continues to do so once you log in. This may include background programs that Windows needs and user-specific items. My laptop hovers in the mid-20s while doing this.


After everything's done loading and nothing is being done, the laptop still uses about 14W. Hmmm, I should have messed around the with brightness to see how much the backlight affected the reading. Oh well.

Opening/Running Programs

I load up a web browser and a bunch of standard Office programs to see what would happen. While loading, the power use goes up to the mid-20s again, then falls back down to the mid-teens. It doesn't seem to matter much how many programs are running at once if they aren't doing anything.

Playing Videos

While running videos, the power goes up to the 20s again, and when playing HD full-screen content, the power touches about 30W briefly. The power seems to hover around the low-20s most of the time though.

Shutting Down

The shutdown process involves doing a lot of stuff in the background, and this shows in the video as a power spike similar to the boot-up process.

How does this compare to a desktop?

I feel very guilty using a desktop with a large monitor, stereo receiver, and bookshelf speakers. Last I checked, the receiver alone burns 35W just by being turned on. Think the reading on an older power meter was around 110 while idling. The good news is that I don't need a space heater in my room.

When doing lighter stuff on the desktop (e.g. videos, surfing), I believe my desktop hovered in the 150W-175W range. Video games pushed it just past the 300W range.

However, remember that power consumption varies depending on what you have running and what you have running it. Being a nerd, most of my stuff is on the slightly-higher end -- not sarcasm because there is some very hardcore and electricity hungry hardware out there that puts my computer to shame.

So what?

From what I can see, laptop computers are relatively efficient to begin with compared to desktops. This is probably by design due to the need for battery conservation, available real-estate, portability, and weight.