My lights turned out black in rendering!
---This article applies to pre-1.6 versions of Corona Renderer. In newer versions "prevent black appearance" option was added to force the light to be always visible as white/colored instead of black---
Corona Lights and mesh emitters with "directionality" other than 0 will always produce such result when seen from a certain angle. It is physically correct as when directionality is enabled, some of the light rays do not reach the camera.
Lights in viewport:
Render, directionality = 0
Render, directionality = 0,5