Talking about the cob led
LED is a semiconductor luminescence device, because of its electricity features, it will used to generate light,  when the voltage is loaded on it.
The input voltage is 3V and input current is 20mA for a certain led.there are many types of led.on the involution, this 3V and 20mA development tendency is the extension of its functions, the led parameter can be evolution in a variety of parameter led.  the 6V,9V led is connected with serial-in parallel-out and they have a stronger light energy.and in the background there needs to be a more professional led device. it name is COB led. COB also is led,designed around the same principle.
There are many led were encapsulated in led device for protection. the cob could have a big operation voltage and current than in single led.