Our recessed ceiling light sizes are named after the size of the hole / cutout in your ceiling not the diameter of the light panel itself. This means that if you have an existing 4” hole in your ceiling, you will go with a 4” recessed light. A 3” light will be too small and have an exposed ring of ceiling hole around it, and a 6” panel will not fit.
See photos below for a visual guide for both the hole cutout and actual diameter of the light itself for all 3 sizes.
Note: there is some leeway, where the hole can be about half an inch larger than the size specified. The outer ring of the light panel will cover up the extra space - up to the given point of its total diameter as listed in each photo. 
If you're still unsure, please contact us and let us know if we can assist you in the process of choosing or installing our Recessed Circadian Light Panels for your ceiling. We’re happy to help in your transition to a fully circadian friendly home.
Electrician installation is recommended.
