Suggested features
The app is great. Here some suggestions for a more complete experience, I'm pretty sure people will be willing to pay you a small fee to get these (premium features):
1. Add a countdown to turn off the lamp, sometimes people want the lamp to be turned on for a certain amount of time then it should turn off itself.
2. Allow people to add a Wake Up time when the lamp turns on automatically, I know that this can be challenging but once users allow the app permissions to manage the phone, you can do the magic.
3. After hitting START the only way you can turn off the lamp is by using the power button, it would be more convenient and intuitive to turn it off by simply touching the screen, as it happens with the demo.
4. Do not close the app when user uses the power button, which as said before in point 3 should be touching the screen.
5. By the way, for point 2, adding an option to include some soothing sound effects would be great. For instance, birds chirping at 7 am with the screen automatically turning on with an initial brightness of 10 and ending with brightness of 40. As the brightness increases the volume should do it progressevily too.
I'm a UI/UX QA expert, feel free to contact me if you need to test it out.
Good luck. 