To think this is unreasonable?! Or am I out of touch

Ask your parents where, in the whole of their home, could they tollerate a bright light?
Let them dictate where you work from all day.
Alternatively, is there an internet cafe or library near their home?

It is unfair that you have a bright light where they have to see it.

I know the feeling. I get this too when I work at parents. I have to be firm and say I won’t come then as I cannot work in te dark. Your choice. I live 300 miles away so I have to work part of time I go there good luck

If you know that someone is guilt tripping you (for having the light on) then as an adult, you either ignore the guilt tripping entirely and carry on putting the light on, or you make different arrangements if the guilt tripping works and you are letting it get to you.
Those are your options.
Complaining about it gets you nowhere.
You already know they are being unreasonable and mean spirited especially when in a bad mood. I wouldn’t want to be there under those circumstances.

Having said that, I was lucky enough to have a house full of family for two weeks over Christmas. Several times, I found myself going round the house turning lights off where they had been left on unnecessarily and I realised that younger generations just don’t pay attention to turning lights off when not needed. Even when all leaving the house, I would have to ask for all lights to be turned off please, especially extra Christmas lights.
I hope not but maybe my family saw me as being unreasonable and a bit mean spirited ?

Their home their rules and perceptions. Take your own desk lamp or limit visits for a time you can be there too (in spirit not just body).

Yes, it’s batshit, however, could you buy a rechargeable light and take it with you when you visit? Fully charged, of course.

Look up the DSE (display screen equipment) guidance as this includes lighting. Home working is an extension of the workplace. Has your employer undertaken a Home Work Risk Assessment of your work station or do they not know you are sometimes working from other locations? The lighting and other conditions (DSE regs cover other requirements too) potentially likely non compliant.

I like this reply.

they sound utterly bonkers

Exactly

People are so weird about lights. I prefer not to have any lights on if there is natural light coming through the windows, but I've noticed many people who will walk into a room that I'm occupying alone and immediately switch on lights without asking me first. I don't know if they think I forgot to turn on the light, or just don't care what my preference is.

But if they were thinking of it as them providing a favour with childcare then they are doing that to allow OP to work, and it’s not a ‘visit’. They can’t have it both ways - they are either not looking after their GC to enable OP to work, and it’s a visit, or they are and it’s not.

Unless their lights would genuinely blow up at being on for more than half an hour they are being unreasonable when their own daughter tells them she suffers headaches without them being on, and she is there to work.

I know OP isn’t after a solution, but surely it would be for them to pick up GC to look after her or look after her in OP’s home, where power usage is none of their concern.

Is there a coffee shop or library close to them you can work in, if you are already in a separate room? Or take a desk lamp, just buy one from IKEA and plug it in? Their spotlights will need changing at some point but if you value the relationship with them or don’t want the fallout from not going, I would just look for another solution.
I do think they are being unreasonable and you are being very accommodating though.

You can change what you do…

Their reaction is really unreasonable but there is nothing you can do to change that.

Yes it's them being unreasonable. You say you don't want people to suggest solutions but you really don't have to put up with this you know. That's the great thing about being the adult child of abusive parents.

Sounds like THEY are the ones being controlling and unreasonable!

You're clearly terrified of your parents and it's clearly them who are unreasonable and
controlling.
They're dictating that you need to take Dd to see them and also preventing you from working without getting a headache while you're there. Can you not see how ridiculous this is?
If they expect you to drive Dd to their house then the very least they can do is provide you with adequate lighting for your work.
If you would truly be eaten up with guilt for requesting a tiny thing like a light when you're already bending over backwards to meet their demands, then you've clearly grown up in a very abusive household and need to work on boundaries. People writing things like "grow a backbone" or offering obvious solutions like "Just dont go there" is because it's unbelievable that you'd even question if you're being unreasonable. It's like writing "My parents knowingly give me an unpleasant headache when I visit, am I unreasonable to mind"!?!

Good grief, grow a spine

Why can’t you go on weekends?

This is a mad arrangement and I hope you can take a step back and see that!

They need to see their grandchild at weekends, evenings, or holidays. You need to stop tying yourself in knots.

Umm, are you paying for a full week of daycare but not simply turning up for one of those days because your parents complain that they don’t see your daughter often enough? Are your parents costing you good money? And then making your life difficult to boot?

Please correct me if I have it wrong. Otherwise, ffs.

If I am right, you need to grow a backbone. You are perfectly entitled to behave as they are behaving but on behalf of yourself and your daughter. Your parents have successfully backed the horse called Self Interest for long enough. It’s time you took a turn.

@Greehsa Take a portable battery powered light with you. They can’t complain then.

Oh and it's also not fair on DD for you to have to work in the evening when you could be doing xyz with her. You can also mention this. Yes not fair on DD to miss out because of a light. What a shame. Etc.

Sounds like you're really in people pleaser mode with them.
You would have absolutely nothing to feel worried or guilty about if you were blunt about it!.
They think you're controlling!?
You say:
Oh yes, it's a shame you can't come to ours. Well, I need to work, so I have to be in a place where I can work.
Yes, what a shame about the light, if only it was ok to have it on. That's really too bad.
Oh well. The optometrist said I need good lighting to work.
What a shame. I'm sure DD would love to see you at the weekend/in a few weeks/when I'm not working/ when you can come to ours.
Repeat. Repeat. Do not worry. Do not feel guilty.
Escape whatever F.O.G. cycle you've gotten yourself into and make it work for you!

I get this. I have it with my mother. It’s a pattern of abuse where you just aren’t allowed to have needs, right? For some reason (and I don’t understand it either) they feel the need to put you in your place and remind you that your needs don’t matter. Does this come out in other ways too? I denied this to myself for years until she started to do it to my children too and that was when I finally stood up for myself (to show my children that it wasn’t acceptable).

Sounds like they are so controlling over the big light they have forgotten to equip you with a backbone whilst raising you

C'mon, I don't know anyone who wouldn't have a firm conversation with their parents. Sounds like you need to not go round for a couple of weeks (if you can muster the confidence to do that)