Why every LED module has a resistor?

Why every Channel letter LED modules has a resistor? The simple answer: to limit the current  in the LED to a safe value.

The detail factor as followed: LEDs are semiconductors, diodes in particular. The current flowing in an LED is an exponential function of voltage across the LED. The important part about that for you is that LED forward current is not linearly related with forward voltage. That is the most important concept of LEDs. Resistors aren抰 like that. The current and voltage in a resistor are linearly related.
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