I work in a small office, there's 6 of us in total, so it's not possible to turn off "some" of the lights without turning them all off.
In the UK, we're now in the Spring season, which generally means brighter days. Because of this, one of my colleagues recently asked if the lights could be turned off. I don't like confrontation and I didn't really say anything. Luckily, for me, their request was met with disgruntled groans so they were left on - since it wasn't quite that sunny yet. However, I am noticing that it is now getting much lighter outside more frequently, so I can see this question getting brought up again.
The reason I would like to keep the lights on is because I suffer with headaches when in a poorly lit room for a period of time (more than 30 minutes is normally enough). Even though the sunshine would be coming in through the windows, this would only be from on direction and from the side. I find that having a light source (that produces a white glow, not a yellow glow), prevents me from getting a headache.
I find my co-workers to me reasonable people, though I find it hard to confront someone.
How could I politely ask that the lights stay on, when a co-worker asks to turn them off?