Led bulbs are very popular replacement for traditional incandescent or halogen bulbs. Moreover, they are commonly use in home or in automotive solutions. LEDs are powered by the constant current. So, if they are directly dedicated to AC voltage, they require dedicated power supply unit (AC/DC converter).
How to check the quality of LED bulbs using your mobile phone?
First of all turn on the bulb. To check the quality of LED bulbs, turn on the camera in the phone and move it close the bulb for a few centimeters. If we see stipes passing on the screen (see photo), it means that this the cheapest possible power supply system and, as a result, voltage supplying the LEDs is not constant voltage. Such a bulb blinks at a frequency equal to twice the network frequency (100Hz) and can be harmful to our eyes. In conclusion, good quality device should not blink!