JD is correct. With the Hue app, you can set all of the lights in a room to any state, color, and brightness you want, and then save that as a named scene for that room. So for example, if I want to set my entire house (4 rooms) to a scene named “Nightlight”, I create a scene with that name for each applicable room. I can then either set each room individually to that scene in the Hue app (GRRRRR), or say “Hey Google, switch lighting to nightlight”. Google Home then talks to 4 different IFTTT applets (4 rooms), each of which sets the scene for one room in Hue.
It works, but is laggy and is a PITA to manage. For one thing, you can’t edit an existing scene in the Hue app…you have to delete the old one and re-save it. This causes some internal ID to change, so the IFTTT applet gets confused and can sometimes no longer see that scene, even though it has the same name. To fix it, you have to edit the IFTTT applet and reselect the new scene from the list.
I’m just starting my first SmartThings app, so it’s going to be some time before I can accomplish anything. But it seems that an experienced developer could tap into the named Hue scenes through the API (I assume), and set any that match a name variable in a ST app.
To complicate matters somewhat, I also have a few switches that control things along with the Hue lights for each scene. For example, I have a WeMo switch that my PC monitor is plugged into. So with one voice command (“Ok Google, good night”), I am controlling 4 Hue lights, a WeMo outlet (PC monitor), a WeMo switch (porch light), and sending notifications to an old Note 3 to trigger Anymote to shutdown the entertainment system.
It works… but there has to be an easier way.