I have seen several requests that beat around this topic, but don’t seem to exactly hit it. Currently when I turn on or off a group of lights using the group control, the lights turn on/off one at a time. This is especially noticeable with dimmable lights. I would like for the lights to all turn on at once or turn off at once to more closely resemble the effect of turning a light switch on / off. Based on the code I have seen around this issue, it is because the items in the group are addressed through a loop turning each light on/off before it moves on to the next one. I have 4 lights in a ceiling fan, and it takes about 4 seconds for the lights to turn on/off. Each bulb takes about a second to turn off. Perfect synchronization is not required, but something closer than one at a time.
Which platform are your lights using? For Hue lights, you can work around this by using groups on the Hue bridge instead. Might be the same for some other platforms.
osram lightify
I noticed this too. I think it’s just a weakness in the Lightify component support. Turning a group of Lightify bulbs on/off from the Lightify app works as a cohesive group. Same from SmartThings as well. I think the HA Lightify component just needs needs an upgrade to support groups.
that or being multithreaded couldn’t HA notice it’s a group and send a turn_on command to each light at the same time (or to a subset of the lights using no more than 3 threads to do it), that kind of thing???
Chiming in here. I would love this feature.
Like @turboc , I have a light fixture with three lights and Hass turns them off one-by-one whereas the Lightify app can turn them off simultaneously when addressed as a group. Surely this behaviour must be possible to implement in the Lightify component?
Pinging @MindrustUK
I gave up and replaced the wall switch with a smart switch. It works perfectly. 
I can understand why you’d give up But I can’t help but want the most elegant solution!
I thought I went with the more elegant solution. The switch controls the power going to the light so I can dim them to any level I like all at the same time. I have one device to automate, not 4 in the case of the light fixture with my ceiling fan. And when I turn off the wall switch, there is still power there so I can control it. With the lightify solution, if I turn off the wall switch, I have very stupid smart lightbulbs.
It’s been a while since I’ve had a chance to look at any of this, at present I’ve somewhat abandoned the Osram stuff as it’s all now attached to a Philips Hue Hub. Manipulating groups should be possible out of the box with the library my previous code was wrapping although I don’t think there’s any provision for creating them outside of the official Osram app. Various other people on other home automation projects may have already done this so you could look into porting their code across.
Hey man, thanks for the reply.
Shame about the abandonment. I was sure it must be possible, so it’s good to see a sort of confirmation. I don’t mind about creating the groups in the app, that’s no problem - I just want to be able to address them.
That’s a good idea Unfortunately I don’t know how to code in Python 
Brilliant!! Thanks for the link