How does the Led light need to be turned on?

-0001-11-30 00:00:00

 The LED lamp is a light-emitting diode with diode characteristics. It has positive and negative poles. If it is reversed, the current cannot be turned on and the lamp will not light. Its working voltage is 1.8-3.3V, of which the red light is 1.8V, white light, green light, blue light is generally 2.8-3.3V.

When the LED works, it must be a constant voltage power supply or a constant current power supply, otherwise it will burn out. LED operation is non-linear and has the characteristics of a diode. For low power, add a current limiting circuit. For high power, a constant current power supply must be used. It does not matter if the voltage is high, as long as the current is suitable.
High-power LEDs must be considered for heat dissipation, otherwise they will burn out, and low power can be used.
LED work, only consider the current, the voltage is high. For example, a 2V low-power red LED in series with a 200K resistor, connected to 1 kV DC, will not burn out. However, the reverse voltage of the LED is not high. If it is reversed, more than ten volts can be burned. Of course, the 1000 volt AC will definitely be bad.

 

Question
Ready to be used as a car daytime running light, 20 9W LED light source from the Internet, the voltage of the lamp is 9v, the current is 150ml, the car battery is 12v voltage, I thought it would be directly connected to the battery, the seller said that there is still a resistor or controller And so on, how to connect? I want to use a switch to control, 2 groups, 10 per group. In addition, is this 9w power consumption too large? Can the battery withstand it? Of course, it is only turned on when the engine is started.
Chasing
LED use must be constant current and constant voltage power supply, if you say the lamp voltage is 9V, the current is 150mA, when connected to 12V, each string is a 20 ohm 1-2W resistor! If you are connected in two strings, buy 10 10 ohm 5W cement resistors, one for each two strings and a switch.