Why doesn't my optical mouse's red LED turn off after I shut down my PC?
The optical mouse's LED stays on because the mouse itself is still being powered.
Just because the computer is turned off it doesn't necessarily mean the USB power is turned off. This is done so that the Power key on some keyboards can be used to turn the computer on.
And why does it stay red? Simple. It is red. Why does the grass stay green...?
I know this question is old, but if someone else(like me for the past few weeks) is looking for a solution to this problem, maybe he/she finds this helpful.
The following solution worked in my case (credits go to Reddit user /u/zelloxy) :
"Start command prompt. Type
powercfg -devicequery wake_armed. Enter
powercfg -devicedisablewake <deviceName>. If that does not solve it try the next one. In my case, my mouse was typed as a keyboard even though it was a mouse. At last it worked."
A lot of computers these days leave power to the usb devices. This is one way for the computer to know it needs to wake up.
Two, there is no standard on how much power is necessary to determine that the device be "lit". For example, on my USB ports, if I plug in speakers that power themselves through USB, the speaker power light stays on when my computer goes to sleep.
If I plug in a Logitech MX Revolution to that port, it stays off. If I plug my wireless keyboard into that front port, the receiver's LED flashes . . .
By definition, this is insanity and thus there is little reason to believe there is an actual deliberate pattern.
The LED is able to stay on because the mouse is powered, yes. But that's not a good answer why it is on. After all, the mouse can't be used when the computer is powered off. The LED being on provides no benefit, and can be a nuisance at night.
The mouse is a little computer in itself. It contains a little microcontroller which coordinates all of its functions, including USB communication with the host.
So the mouse should be able to notice that it has not been polled by the host for some time, and shut down the LED. (There may even be other ways in the USB protocol to infer that the host is down.)
This feature could have diagnostic value also. The LED being on would confirm that the host is interacting with the mouse, not only providing power. (A really useful behavior would be, when the mouse is powered up, to flash the LED several times to indicate "I have power and have started up!" and then turn it off if there is no communication with a host.)
So in other words your mouse isn't sophisticated enough to implement the behavior of shutting down the LED when it's not in use.
It stays on because there is still power in the system.
Even if you unplug it from the wall it will still take a minute because your PC has power in it, most probably stored in the power supply capacitors. To drain it repeatedly press the power button.
However this isn't important because it does no harm but if you want to turn it off go find the relevant setting in the BIOS.
Those answers are bad and quite insulting.
He is clearly not asking why the light is red, or any technical details about how a mouse stays on, because it is being powered.
It is blatantly obvious, that what he is asking, is why his laptop (or OS), keeps powering his mouse, when he turns it off.
It is not relevant, if it really bothers him that much. It clearly shouldn't be on, when the computer is off.
There are several reasons, why some computers leave usb devices on, even though the computer is shut down. One reason is, so that you can power on the computer, via USB devices, such as by pressing a key on the keyboard. Another is, that you can keep charging devices, such as your phone/tablet, while the computer is off.
For my stationary, I was able to adjust this setting in the bios. For my laptop, I still haven't figured out how to change it. It stays on, even when the laptop is on battery. Obviously I don't want my mouse to be consuming the battery, while the computer is off.
I have ran across this problem in other people's computers and have come to this one simple conclusion. The problem doesn't reside in your computer, but rather in the mouse. I have found that changing out the USB mouse fixes this. I like to refer to this problem as "Mouse Insomnia".