I've searched and haven't seen anyone report this problem. In fact, it looks like several people were trying to disable the keyboard backlight!

Briefly (in case the context provides a clue):
-N810 was (mistakenly) left on, attached to charger, screen locked for 1 - 2 days

-N810 was frozen in that state when I went back to it (even power keys wouldn't shut it down -- had to remove battery)

- left battery out for a few minutes, then powered up

- worked fine except the keyboard backlight didn't work

- powered off normally

-left battery out for about 6 minutes while searching forum

-put battery back in but didn't power on -- plugged into charger for about 10 min until fully charged (since people with power issues reported doing that when they couldn't boot up. Figured it couldn't hurt.)

-turned on and everything is again working normally EXCEPT when I slide the keyboard out, the keyboard backlight doesn't even pretend to go on.

Any thoughts? Thanks.

OK, am I the biggest loser ever and just shouldn't expect the backlight to come on because I'm in DAYLIGHT?

I just seem to always remember the keyboard backlight coming on, even in the middle of the day. I could be misremembering, and I do use it more in the evenings/nights.

Can someone confirm whether this is an autosetting and I just shouldn't worry about it?

Thanks.

Problem solved -- it works in the pantry!

Um, do you think this mean I need to keep more daylight hours??

The time of day does not affect the backlight function, but the overall ambient luminosity does.

Try opening the keyboard while obstructing with a finger the light sensor (it is the little hole on top of the camera).

Yup, thanks for the response. I feel really silly, but when I'm at home during the day (a house we've customized to let in sunlight via solar tubes), I'm at my laptop.

It's usually in lower-light situations that I use the tablet, hence the backlight always seemed to come on for me. And, since the thing had just frozen on me for the very first time, I guess I was particularly nervous that something hadn't gone back to normal.

Oh well, live and learn! Of course, there's a different question I really do want to post now, but hesitate to do so after this incident!

post away someone will enjoy your question