Even on the hottest and driest days, rays from the sun are too weak to ignite a fire. But with a magnifying glass (or, in some unfortunate cases, a glass garden ornament), you can focus sunlight into a beam bright enough to set tinder ablaze.
![](https://scx1.b-cdn.net/csz/news/tmb/2021/whatdoeslumi.jpg)
Source:
https://phys.org/news/2021-02-luminosity-particle-physics.html