you can use a light sensor to detect the real sunrise outside,
I don't think that's the idea... The idea is to simulate sunrise when YOU want, while it's dark outside.
This doable, but it's a BIG 1st-time project and you'll have to take it one step at a time.
I built something similar several years ago (with a different microcontroller). I took a couple of shortcuts. I used a programmable [u]X-10[/u] controller so I didn't have to build a clock. And, I used a separate "desklamp" attached to the bed's headboard so this set-up can be independent of the main lighting. (The overhead lamp is also X-10 controlled and it comes-on with a separate X10 command at the end of the 10-minute dim-up period.)
So... I essentially have a dimmer-box the plugs-into a timer, and a lamp that plugs into the dimmer-box. When power is applied to the dimmer-box, it starts dimming-up. Then, it stays on 'till power is removed (by the external X10 timer).
... how to communicate with bluetooth
I've never done bluetooth. There are bluetooth shields and maybe someone else can give you some help & suggetsions.
b]HOW to control LEDs so that it really looks like a sunrise or sunset or night sky
I'm not sure what you want to do for "night sky", but for dimming you have a couple of choices -
There are dimmble LED incandescent replacements that you can buy at a hardware store or home improvement store. (You have to make sure they are dimmable). An incandescent dimmer works by turning-on the AC power for some fraction of the 50 or 60Hz waveform. (That's how my dimmer works.) You need an isolated phase detection circuit and an isolated TRIAC-based power control circuit.
Or, there are special high-power "constant current" dimmable LED power supplies ([u]examples[/u]). There are controlled by a 0-10VDC control signal or by 10V PWM. The Arduino puts-out 5V, so you have to add a transistor or MOSFET (and a 10V supply). The Arduino can also put-out PWM which can easily be filtered to DC if needed. This a LOT easier than building an AC dimmer, and the isolation is built-in, so it's safer to build and experiment with.
Another option would be to build your own constant-current LED power supply, but I wouldn't recommend it.
As you can probably guess. I hate getting out of bed in the morning! :D When I was building the "sunrise simulator" I built another box, controlled by the same timer. It's a little "alarm clock beeper". When power is applied, nothing happens for 10 minutes while the other box is dimming-up the light. Then when the light is fully-bright and it's time to get up, it makes a gentle "beep". 30-seconds later it beeps again. It beeps every 30-seconds, and after two minutes (actually after 12 minutes) it beeps twice, then twice again at 2.5 minutes. At 3-minutes, I get 3-beeps, etc. (I think this can go up to 15-minutes.)
(This could have all been built into the same box with the same microcontroller, but I was learning and trying to keep things as simple as possible.)
CONFESSION: None of this is working right now... The freekin' software to program the X-10 controller won't run under Windows 7 and the timer has drifted-off by a couple of hours... A newer programmable X-10 compatible controller that can dim my other lights is about $300, so when I get around to it I might re-install Windows 2000 to re-program the thing.