In the Ecopedia, the SUPPORT > LIGHTING > KITCHEN CEILING LAMP
Kitchen Ceiling Lamp has a diminishing return of -50%.
All other ceiling lamps have a diminishing return of -30% (higher and lower tiers)
In fact, other than this, the ONLY other light that has a non -30% diminishing return is the Steel Searchlight, and it's uniqueness could excuse that IMHO, but it might require a review too just to be sure.
This just feels like an odd miss that could be reviewed to be sure it's supposed to be that way.
Version 9.7.5
In the Ecopedia, the SUPPORT > LIGHTING > KITCHEN CEILING LAMP