WTH: Group brightness control

Month of "What the heck?!"
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1

I’ve noticed a strange behavior with light group brightness control.
When I increase the brightness of a group, it only changes the average brightness, not the individual lights.

Example:

My “Living Room” group has three lights with different brightness levels:
Living room (brightness 148)

  • Couch (255)
  • TV (123)
  • Desk (66)

When I increase the group brightness by 20% using this service call:

action: light.turn_on
data:
  brightness_step_pct: 20
target:
  entity_id: light.living_room

I expect each light to become 20% brighter. Instead, all lights are set to the group’s average brightness (199). This even makes the “Couch” light darker!

Living room (brightness 199)

  • couch (brightness 199)
  • TV (brightness 199)
  • desk (brightness 199)

Expected behavior:

Each light within the group should increase the brightness individually, not just the group’s average.