It is pretty common to do a traffic light setup at some point, even if it is just to play with the software logic of it all.  These help take those efforts to the next level and are useful for general indicators such as coupling with the soil moisture sensor to show the status of the plant soil moisture. The modules have current limiting resistors built-in, so they can be connected directly to the pins of an MCU.  You can even plug it directly into the female header of most Arduino boards where you have 3 digital pins next to a ground, such as using the Uno pins 11, 12, 13 & Gnd.  The LEDs are lit when a logic HIGH is applied to the pins.

Specifications

• Large 8mm Red, Yellow and Green LEDs
• LEDs active HIGH
• Built-in current limiting resistors
• 3.3 and 5V compatible