One of the most common misconception that I have to deal with is the idea that light can ONLY be created upon an atomic transition. You wouldn't believe how many people believe that this is the only way to create light. This shows a severe lack of understanding of classical E&M and Maxwell equations.
The one example that I typically use to counter such misconception is to tell people to figure out how synchrotron centers around the world create light, or EM radiation. In particular, many of these centers generate x-rays to be used for various purposes. These x-rays are generated via "charge acceleration", either by using the bending magnet, or using the insertion devices that essentially cause the electrons to "jiggle" up and down (or sideways) as if they are at the end of a spring. These cause the generation of EM radiation. No "atomic transition" is involved.
This video shows clearly how x-rays are produced at the Advanced Photon Source at Argonne National Lab.