The sun is normally in the sky above us, we build buildings with lights on the ceiling or high up on the walls, so it's reasonable that an image with a light-so

The sun is normally in the sky above us, we build buildings with lights on the ceiling or high up on the walls, so it's reasonable that an image with a light-source above would be more understandable than one with a light-source below. It's very unusual for a light-source to be exactly aligned with the thing it illuminates, so unusual that if you see it, it looks wrong[1]. It's reasonable that an image with a light-source to the top-left or top-right would be more understandable than one with a light-source directly above. As for why "left" rather than "right", I don't have a good answer. When Microsoft redesigned Windows 3.0[2] to make the buttons look more like buttons (instead of just rectangular or rounded outlines), they decided to put the light-source at the top-left rather than the top-right. Why they chose that direction I don't know, but I notice the mouse-cursor also points to the top-left, the most important menu (the system menu) is in the top-left, the title bar is at the top and the menus in the menu-bar are left-aligned, etc. etc. I don't think there's a neurological reason why shading should have a top-left light-source, but if you're making an interface for people who read left-to-right, top-to-bottom and you visually organise everything in that same order, it makes sense to align shading in the same way as everything else rather than have it be The One Thing Out Of Place. [1]: https://www.amusingplanet.com/2017/04/lahaina-noon-when-shadows-disappear.html https://www.amusingplanet.com/2017/04/lahaina-noon-when-shad... [2]: https://guidebookgallery.org/screenshots/win30 https://guidebookgallery.org/screenshots/win30