The moment it clicked for me was a corner of an old study, a wide pine desk with nothing on it but a laptop and too much overhead light making everyone look tired at seven in the evening. I set an old brass lamp with a green glass shade on the corner of that desk, pulled the overhead light off, and the whole room changed its posture. That's what a good desk lamp does. It gives a room one soft, aimed pool of light instead of one harsh flat one, and your eyes stop fighting the whole space just to read a letter.
If you've never owned one, start plain and start adjustable, something with an arm that moves and a shade that angles down rather than out, because a fixed lamp looks fine in a shop and becomes a nuisance the first time you need the light somewhere else on the desk. Brass or bronze with some age allowed to show, or a painted metal base with real weight to it, will sit easily with almost anything you already own, a rolltop desk inherited from a grandmother, a plain modern table from a big box store, a kitchen counter doing double duty as a workspace. I've put the same lamp style on a scarred oak desk in a rental and on a painted secretary that had been in the family three generations, and it looked right in both places, because good lamps borrow from old design even when they're brand new, and that borrowing is what lets them sit next to almost anything without an argument.
What separates a lamp that lasts from one that dies in a year comes down to the joints and the weight. Pick one up before you decide. A cheap one feels hollow and light, the arm wobbles at the joint, and the shade is glued rather than fitted with a proper harp or finial. A well made one has some heft in the base so it doesn't tip when the cord gets tugged, the swivel points are metal on metal rather than plastic sleeves, and the finish, whether it's brass, bronze, or painted steel, feels like it was meant to age rather than scratch through to bare metal the first week. The old ones I've rewired for clients still swivel smoother than lamps made last year, and that's not nostalgia talking, that's just better hardware.
The one mistake is buying on looks alone and skipping the test of moving the arm and shade through its full range right there before you buy it, because a lamp that can't actually point where you need it is just a sculpture that uses electricity.