The lights on your Philips SmartSleep indicate its battery level. Find out here the meaning of each color.
Battery indications on Philips SmartSleep
A slow pulsing amber light means that the battery is charging normally.
A fast pulsing amber light means it is connected to an underpowered charger (e.g. a laptop, we do not recommend using this for charging).
A double flashing light followed by a pause and a double flashing amber light indicates the battery is depleted to a very low level. Your device needs to be charged with its charger. Use the right charger and charge it long enough (2-3 hours).
A solid green light means the battery is fully charged. You may disconnect it from the charger to save power.
If the light is off this means the battery is fully charged and the device has automatically entered low power mode. You may disconnect it from the charger.