According to the Emory sleep disorders laboratory, you should refrain from using your tablet or phone before bedtime because the light from the tablet shines directly into your eyes. Even the famous Mayo Clinic got into the act last week by suggesting that tablet and phone users turn the light down on their slates before bedtime. The Clinic said that devices emitting more than 30 lux in light can affect melatonin levels in the body.
The Mayo Clinic suggests that you will be alright if you hold your smartphone or tablet 14 inches or more away from your eyes, even at maximum brightness. At that distance, only the Apple iPhone 3G had a reading of 30 lux. If you lower the brightness level, you should be able to bring the phone to your face. Doing that, the Apple iPhone 4 measured only 8 lux, making it safe for insomniacs to look at.
If you're having trouble getting a restful sleep, your best bet is probably to turn off the phone and the tablet and close your eyes. 40% of adults who are awoken by their smartphone just end up using it. Unless you're expecting a call, perhaps you can shut down your phone or at least turn off the volume. If you have an Android flavored phone, TeXT can send out a alarm if someone you know needs you in case of an emergency.