Why is he upset over a light?

When people get stressed, for example with their job, they often compensate for the feeling of a lack of control by trying to 'control' other aspects of their lives. 

The kitchen that was perfectly fine yesterday suddenly needs deep cleaning, for example. Not because it is dirty but because cleaning it, and trying to keep it clean for that day, satisfies that sense of loss of control. People fall into routines and get irritated when those are interrupted.

One of the issues with Covid is spouses sitting in the house together all day. Every day. People need space and need their partners to just leave them be for a few hours.

What you are describing is pretty typical. I suspect your husband at the moment is busy in work and stressed. He has a routine which he uses to control some of that, and his work is the part of the day where he gets a bit of space by himself.

By walking in and turning off the lamp you basically interrupted that, so his irritation has nothing to do with the lamp, and everything to do with just wanting to be away from you for a while. Or to put it another way ... if you weren't working from home, and your husband just suddenly showed up in your office and started rummaging around, chatting to you, turning off lights you'd turn around and tell him 'go away ... I'm in work ... I'll see you later!' The fact he's working from the bedroom doesn't change his feeling that he's at work then, not at home.

This sort of behaviour is pretty common on ships, submarines, anywhere people are in close confinement with one another. You just both need to be mindful of the need to escape from one another for a few hours a day. It doesn't mean he doesn't love you. It just means he's in work, has stuff to do, and at that moment in time you are a distraction. Not a biggy and easily sorted! 

that is a stupid thing for your husband to get upset over... just tell him "fine, you pay the whole electric bill then"

is work stressing him out??

Are you both twelve years old or what?  Who cares.

I've read a few of your questions, and like ALL married couples you do seem to need to do some work. Here for example, you appear to make a mountain out of a molehill: you will be coming across to him as being critical - and you really don't want to start being a nag! Try to be more accepting of his decisions and preferences. You're not his mother. 

Reading books like Dr Phil McGraw's excellent Relationship Rescue helps to give us deeper insights into how relationships work. As he writes, it isn't only for people whose relationships are in trouble. Also how to get reluctant partners to read it. There are other excellent books, of course. 

It's called cabin fever and being sick of being cooped up all the time and we all have it. No one is at their emotional best right now. 

You’re both wrong.  All he had to do is say Hey I like that light on can you turn it back on for me.

And he hadn’t left the room. So all you needed to do was Say hey do you want this light off.  

I think the "Wife" is all about trying too save $$ on the electric bill? "Waste Not, Want Not." If you don't need the light On, then why have the light On? I'm the same way with all utilities, they aren't free and someone has too pay, that would be Me! Lots of people struggle to make ends meet ever month and grew up less fortunate to where you had to be careful with your spending habits. Wife, a penny saved is a penny earned.......remember all these people who are now Crying Over How They Can't Pay Their Bills, Do To Not Having A Job? YEAH, should have turned those lights, water, heat and air condition off when you could have. My Grandfather always said, "Never Get Above Your Raising, Falling Back Down Is H_ ll" 

I’m on your husbands side on this one. You told him you always turn the light off when he leaves but you turned it off when he was still using it. You had no business going in and turning off the light. 

This is ,now, your 1,098th answer.  You must have written your post wrong? You said you walked in and turned off the lamp while he was sitting there working?  Now what could be wrong with that ! Ho hum.....

Having more than one light source is ideal for reading and writing. Rather than get upset with you a simple request for you to please turn it back on would have been more appropriate. Tho it does seem rather ridiculous of you to be running around after your husband and fixing things. If he leaves it on and then leaves the room for an extended time, it makes sense to turn it off. However if he is going to be in the room most of the day then it's easier to just leave it on. 

People work with a certain level of brightness. If you turn it off, they can’t work. 

Why did you turn off the light when he’s there. You said it yourself, you turn off the light when he’s not there. He could have turned on the light when he’s working and you didn’t notice. 

id rather stab my foot with some scissors than read this.

So you're in the kitchen working and he's in the bedroom.  Why do you wait till he leaves to run back into the bedroom to turn off his light.  Is it bothering you that much?  Why don't you tell him as he's walking out the house, "honey, don't forget to turn off the light on your side of the bed."  It sounds like you have an issue with control.  "I'll do it and he won't even know it."  So he beat you home this morning and you just couldn't resist.  You had to go turn off that light while he was sitting there.  Is one more light gonna raise your light bill that high?  But you have the kitchen light on too so you can see, right?

You likely weren't disrespecting him but maybe he felt like you were. After all, HE'S the one who was in the room. My husband would react to me playing "light monitor" as well. But continuing it into being upset about it and in a huff ongoing? Something else is also going on. Regardless, he likely thinks he has the right to determine how much light he wants in the room he's actively working in. Lots of times there isn't a "right" or a "wrong". Mostly it's about showing respect. 

The light on his desk is a reading lamp. The room light illuminate the entire room . When you switched off the light the brightness was gone . The dullness in the room would have annoyed him .You should have said I am sorry and switched on the light again. That would have settled everything .

I don't know how long you've been married but it appears that you're just beginning to realize that there is a difference between dating and actually 'Living' with each-other.

And it seldom ever comes without some conflictions.

And,
that would include but not be limited the kind of conflictions that some might seldom bother mentioning without the risk of seeming unreasonable.

Example:
In our household we have a TV in virtually every room in the house except of course the bathrooms,
so there's no reason everybody can't just watch whateverTF they want with seemingly no excuse for conflictions,,,right?

Witch doesn't explain why I can't just go to the kitchen to get a drink or even leave the room where I'm watching a TV for a moment to use the can without somebody changing the DodGam Moth-fkn channel!,,
After all, Of COURSE I'm watching that TV and just because I left the room for a moment doesn't mean I'm not STILL watching that frkn TV!

Another one:
Of COURSE nothing showing on a TV is more important than the Love of my Life & Mother of my Children,
but Goddamnedit as long as My feelings are important too, then the least somebody can do is wait for a frkn commercial to demand my undivided attention!

Another one:
Whether it's a tool, a gadget or widget, when I leave something out someplace there is absolutely NO reasonable reason NOT to expect to Find it right where I left it. 
That is unless somebody thinks it should be removed & put away because "that's not where it belongs", 
thus prompting me to wonder if I've completely lost my mind.

Even though I wouldn't have Put it there if I didn't Want it there,
and as long as that's where I expect to find it then Hellooooo! where I put it is EXACTALLY where it belongs! 

Another one:
 
The key to most successful relationships is of course Communication, communication and Communication,,                                                                                                             But Hellooooo Again & Again!

Saying something more that twice in 5 minuets is 'Nagging'.
and,
more that 4 times in 10 minuets is just Beating a Dead Horse! 

So,
You've seen your way clear to turn off a light that your Husband leaves on when he leaves a particular room until he finally said something about it.                                                                                                                                                                                         What..are you the light police or something?

Hahahahaha!! Nothing to get in a lather about & hardly worth mentioning without the risk of seeming unreasonable, right?.

But,
he leaves it on for a 'Reason' and even though his reason may seem 'seemingly Un-reasonable',,Reasons are reasons & to each their own!
Since for some reason,
he obviously prefers the light to remain on just as 'He' left it.

So,
unless you're some kind of unreasonably obsessive compulsive neat-freak or fanatic energy conserver or something,
you might consider giving your husband a break and stop making it appear that you think you need to obsessively pick up after him & make adjustments to things whenever he leaves a room he uses intending to go full-circle & get back to some-o-those things. 

I'm confused why this upset him and why you felt the need to post it.  It sounds like a trivial, childish argument on BOTH sides.  I would have said, "Sorry, I didn't mean to upset you" and gone on with my day.

He was right, he was home.  But it became too out of hand.....

There is something underlying going on; it is not the light. He feels he is losing control for some reason. Just leave the light on from now on. 

I bet there's something much more serious and deeper than a light that is what's really upsetting him.

Respect your husband and show kindness and be humble all the time
Accept your weaknesses and lower your gaze 

@Hope
Is one more light going to really run up the light bill that much to put someone in the poor house?  I could see if he had every light on in the house even in rooms he wasn't in but this is the light in the room he's WORKING.  Should he work in the dark to save a few pennies?