That does not work either. When I change the slider I get this in the log:
May 06 13:59:19 raspberrypi hass[4129]: INFO:homeassistant.core:Bus:Handling Event call_service[L]: service=turn_on, service_call_id=1979603472-2, service_data=brightness={% input_slider.hall_light_brightness.value %}, entity_id=[‘light.upstairs_hall_1’], domain=light>
May 06 13:59:19 raspberrypi hass[4129]: ERROR:homeassistant.core:Invalid service data for light.turn_on: expected int for dictionary value @ data[‘brightness’]
It appears to be sending the template string instead of a numeric value.
What I really want to accomplish is controlling several lights brightness with one slider. I have a fixture that has 5 hue bulbs in it. It is not practical to adjust each of the bulbs to the same brightness manually, I want to treat them as one light. See topic here Group Light Controls - #3 by GraysonPeddie