Updated March 12th, 2016 12:08 - Added bits about Wink & Saffron's Silk
I had high hopes for these new C series light bulbs from GE. The introductory starter kit includes two bulbs each of Sleep bulbs, and Day bulbs.
The day bulbs function like your standard led bulb with the exception that you can adjust their brightness on-demand with your smart phone. I think they can also turn on or off if you set scenes such as the ready-made scenes Wake Up & Bedtime scenes. When adding day bulbs to the CBYGE app, there is a tickmark that says Follow The Sun, but this appears not to do anything at all for the Day bulbs. I was a bit disapointed, I thought at the very least the day bulbs would automatically change in luminosity (think intensity or brightness), starting dim, brightening up at noon and then dimming at dusk. No cigar in my testing.
The sleep bulbs are what I was excited about. And if given a choice, I would only purchase sleep bulbs and none of the day bulbs. Unfortunately the starter packs force you to buy both. A customer support representative on the phone mentioned that they may sell sleep bulbs a la cart or packs in the future.
The sleep bulbs can change color temperature as well as luminosity. It can't quite reach the luminosity of the day bulbs, but subjectively speaking the difference is not much. It was bright enough for me, especially if you have light fixtures that use multiple bulbs. These bulbs are supposed to be able to emulate the color temperature and luminosity shift as the sun with the feature Follow The Sun, unfortunately in my experience the behavior is unreliable.
The fact is the technology relies on bluetooth, and that I have an iOS device. iOS devices like iPhones, iPads etc do not let applications run in the background without the user's explicit permission to allow it to (if the app even supports and gets approved for it). The CBYGE app does not have this feature yet, and so the app only runs for a few minutes after you close it, it will go to sleep when your screen sleeps, or when you switch to a different app.
I didn't think this would be a big deal, but it is. I expected the bulbs to have onboard scheduling capabilities, after all there are only 3 different shifts, AM (cool, bluish), Day (whitish) and PM (warm, yellowish) which would circumvent this issue with smart phones.
Unfortunately the C bulb require smart phones to be present, have bluetooth on and connected to the bulbs, and app in the foreground for the Follow the Sun feature to work. A huge disappointment for me, this was the biggest draw for most people in buying this product, better circadian rhythms! More energy and focus during the day, and feeling tired at night for a deep and restful sleep.
So, generally the lights work like regular light bulbs, the sleep bulbs you can change color temperature slightly, the day bulbs only luminosity. The lights do stay at whatever setting in which they were last used (an improvement to Philips Hue which would reset to white every time the power went off then back on, a royal pain if you want to use smart lights with switches or if you live in a house with temperamental electricity), but that's not what was promised.
If the iOS app had background sync the experience would be much better, but the app doesn't have or use that feature yet. I was unable to find any features whatsoever for C by GE in the system preferences, nor notifications settings at all which surprised me, virtually every other app in the apple store has an entry in there.
At present only the phone that adds the lights will be able to control the lights until GE fixes the Create A New Account form, specifically the password field. It kept yammering about using numbers and letters (my password certainly used both, I generate strong passwords with 1password). I read a comment on the apple store saying that the first character could not be a number, it had to be a letter, then a number would have to come somewhere later in the password. I tried that, and it still didn't work for me. I even tried not using special characters, using short passwords, medium length passwords, to no avail. GE needs to specify their password requirements clearly and sort that out.
Personally I think C lights are doomed unless they somehow make the bulbs store the Follow the Sun settings internally and work for the most part without wifi/bluetooth etc based on an internal "clock" (if it has one). I sure am not interested in whipping out my phone to change the color temperature or intensity in each room three times a day. The range of the bulbs is quite short by the way, when I was in my room, I could not see the bulbs in the living room which was maybe 5 yards/meters away.
My recommendation is to hold off on purchasing if you purchase at all. Wait to see what GE's commitment is to improve the apps and what they can do about the bulbs themselves. These bulbs still have some potential. It is possible that the bulbs work much better for Android users, so check for other reviews to see if this is the case. I expected it to work well without relying on smart phones, and it still might be possible. An agent told me over the phone they do have a hub from a different product that is supposed to work with the C bulbs. I'll find out more about it.
Update: After doing some digging and calling a representative at GE about an older smart home product Wink (I had heard wrongly from I think a new employee for GE C that Wink could control the C bulbs. That idea was put to rest, the C bulbs are just Bluetooth, and will not be able to connect to the Wink (or any other wifi based hub).
So, with that my final recommendation is to not buy if it's automated circadian rythym lighting you're after. For now I'm looking to Saffron' s Silk light bulb, hopefully they'll be the ones to get it right.