One of my favorite facts about sunspots is, they’re still in extremely bright, they’re only dark due to contrast. An electric arc against a sunspot would look black by comparison (given typical logarithmic brightness measurement).
- photosphere temperature: 5870 K
- sunspot umbra temperature: 3000-4500 K
Per Stefan-Boltzmann law, this can make the photosphere up to (5870/3000)⁴ ≈ 15 times brighter.