The light on your Apple Wireless keyboard should blink only when it is in discoverable mode. This means that if your keyboard is searching for a connection, the light will blink. Once a connection is active, the light will turn off. When connecting your keyboard to a device with which it was previously paired, the light may give only a single blink or two as it quickly locates and connects with your other device.
If your keyboard light is not blinking and you have pressed the power button to turn it on, the keyboard may be paired with a different device. For example, if you normally pair your keyboard with your Mac but want to pair it with your iPad, if your Mac's Bluetooth is on when you turn on the keyboard it may automatically link up with the Mac before you get a chance to pair it with your iPad. Turn off the Bluetooth on your other devices to avoid this problem.
The Apple wireless keyboard remains in discoverable mode for only three minutes. After this, it will shut off to preserve your battery. If you turned it on and let it time out before pairing it with any device, press the power button again to place the keyboard back into discovery mode. The timeout feature applies only to discovery mode. If your keyboard is paired, it will not time out while the connection is active unless your battery power runs low.
The Apple wireless keyboard works best if you turn on the Bluetooth setting for your computer or other device before placing the keyboard in discoverable mode. This allows the devices to find each other more quickly. Tapping a few keys on the keyboard can wake up the connection if your keyboard has gone into standby mode. This mode happens when you have disconnected it from a Bluetooth pairing but the automatic shutoff has not timed out. When you turn the Bluetooth on your other device back on and tap a few keys, the keyboard will become discoverable and generally will pair quickly, often with only a single flash of the light.
Your light may not blink if the keyboard is not receiving enough power. If you encounter this problem and the keyboard does not work, replace the two AA batteries inside the keyboard with a fresh pair. The battery access panel is opposite the power switch. If everything else appears to work fine but your light never blinks, there may be damage to the light itself. This will not affect your keyboard's operation.