How much power does a computer monitor left switched on use?

Question

It's a little niggling annoyance that always gets me in my office that when I work overtime and leave the office after everyone else I see row upon row of little orange lights where people have turned off their computers but left the monitor switched on.

I'm wondering; are there any estimates for how much power a monitor left in this condition uses?

I'm guessing it is not so much power. But surely more than if you actually turn it off? Or else why is there an off button...

If I can get some solid proof of it using energy then I can bravely and anonymously make a poster to remind people to save the planet by turning their screen off! ... or if I get proof that it makes no difference then I can have a load off my mind.

Answer 1

Usually its around .5-10 Watts depending on the make/model/size etc. I would recommend getting a kill-a-watt meter and checking a variety of monitors to get a rough idea of the average. Then you could bring that up with regard to yearly savings. A 3 Watts average across 20 monitors per year is not nothing.

Answer 2

Monitors typically have 3 power levels:

On -- you're looking at one. Standby -- screen is black, but the electronics are active. Sleep -- circuits are off except for a small one to monitor the line to the computer Off -- it turns into a fancy cookie tray.

I'm using a Dell U2412 21" monitor. I went to their web site and looked up the specs.

Max 72 watts, Typical 38 watts, Sleep/Standby Under .5 watts.

Look up your monitor model online to check. Your mileage may vary.

Given that the average North American household uses about 1000 kWh/month, if your monitor were in actual use all month (720 hours) at 40 watts it would use 28800 watt hours or 28 kWh. About $3 to $5 depending on your power rates. Most monitors are set to go to sleep after a few minutes of inattention. You are talking about cents per month.

In passing: Turning your computer off is a bad idea too.

My computer right now in active use (Mac Pro, 4 processor 6 drives, 3 monitors) is drawing under 200 watts. Half that is the monitors, half the computer. If it doesn't sleep at all when I'm away it uses 2.4 kWh/day -- about 40 cents at my power rates. That's $240 per year.

Ouch! you say. But the flip side is my computers don't break down. When I was sysadmin for a university math department, I averaged three disk failures per year -- out of 300 computers. With the standards of the time I should have had 15 failures per year. How much is your time worth?

Answer 3

Nowadays manufacturers all provide roughly the same numbers when it comes to power consumption of their monitors in "stand-by", "active off", "power saving mode" or whatever they call it. It's below 0.5 Watt or sometimes below 0.3 Watt. So assuming people turn off their computer and the monitor automatically switches to such a mode, then in theory you could save somewhere between 0 and 0.5 Watt by turning the monitor off as well. But that's in theory....

Power off isn't always off

For quite a bit of monitors it doesn't really matter if you turn it off or not. Let me show you a few random specs I found online (no affiliation to any manufacturer):

32" Asus LCD UHD monitor:

Power Saving Mode: < 0.5W
Power Off Mode: 0W (Hard Switch)

27" Dell LCD monitor:

Power Consumption (Active Off) - Less than 0.5W
Power Consumption (Switched off) - Less than 0.3W

28" Samsung QLED UHD monitor

Power Consumption (Stand-by): 0.45W
Max Stand By Power (DPMS)¹: 0.45W

^{1 "Energy consumed by a monitor while off or in sleep mode, as per Display Power Management Signaling"}

For the Samsung monitor it doesn't matter if you turn it off or not, and this monitor isn't an exception. I found various monitors from different manufacturers that do exactly the same. Bottom-line is that you'll have to check your monitor's power consumption specs and/or you may need to get a power-kill-switch.

How much will you save?

Let's assume that the actual power consumption of your monitor is 0.45W in stand-by mode and that you have a hard power-off switch. Now the number of hours people work varies per country. This Worldatlas article lists 1371 working hours for Germany and 2246 for Mexico as low-end and high-end numbers, so let's take (2246 + 1371) / 2 = 1809 hours per year as an average. A year has 364.25 * 24 = 8742 hours in total, so the calculation is (8742 -1809) * 0.45 / 1000 = 3.1 kWh of energy saved per year for turning 1 monitor off directly at the end of every work day.

The average kWh in the US for residential users costs 13 cents, so after one year of doing this you will have saved about 40 dollar cents per monitor.

Answer 4

If the lights are orange, as you've said, then the monitors are in standby, and are using a minimal amount of power (power to light the amber LED, and power to wait for a wake signal).