Most people buy a desk lamp based on how it looks. That’s fine — a lamp is furniture, and furniture should look good. But if you’re going to use it for actual work, there are three numbers on the box that matter more than the shape.
The three numbers that matter
Every decent lamp will list its brightness (lumens), its colour temperature (Kelvin), and — less often — its colour rendering index (CRI). Most manufacturers hide the third one because it’s the hardest to fake.
Lumens: how bright, actually
For a desk lamp you’re going to work under, you want somewhere between 400 and 600 lumens at the surface of the desk. Below 300 and you’ll find yourself squinting by mid-afternoon; above 800 and the contrast against the rest of the room becomes tiring in its own way.
Kelvin: warm or cool
Colour temperature is measured in Kelvin, and it goes the opposite way you’d expect — a lower number is warmer. 2700K is warm white, close to a traditional incandescent bulb. 4000K is neutral. 5000K and above is a cool blue-white that reads as clinical. For a desk lamp in a home, 2700K–3000K is the sweet spot.
CRI: the number nobody talks about
CRI stands for Colour Rendering Index. It’s a score out of 100 that tells you how faithfully the light shows colour compared to natural daylight. For general reading, anything above 85 is fine. For anything involving colour judgement — painting, textiles, cooking — you want 90 or above.
TL;DR
400–600 lumens, 2700–3000K, CRI above 90, smoothly dimmable, weighted base, adjustable shade. If a lamp meets all of those, it doesn’t matter what it looks like — it’ll do the job.