A traditional LEDs (Light Emitting Diodes) recieve power and output light. Typically, these are packaged in groups of three or four coloured LED emitters (Red, Green and Blue / White).

These LEDs can be controlled either via Constant Voltage (CV) where all LED's are dimmed through PWM (pulse width modulation) that works by very rapidly turning them on and off (pulsing) for periods that visually appear as a steady dimmed light. We adjust the brightness level by adjusting the percentage of the time the lights are on (100%) to the time they are off (0%). This results in all LEDs reacting in the exact same way (colour and intensity).

Whereas a Pixel LEDs, or IC (integrated circuit) as they’re often referred to, regulate their brightness based on a data feed. Provide power and a data signal, and you can change the colour without having to use individual dimmers on a per-LED basis. Populating a flexible PCB with this type of LED provides the end-user with the ability to control every single pixel LED on the strip individually to create more creative visual effects than simply dimming all LEDs on the strip at once.

Serial Peripheral Interface (SPI) Data is a synchronous serial communication protocol commonly used for communication between a controller and a integrated circuit (IC) chip. These IC chips are commonly found in pixels (also known as "smart pixels"), these pixels can be made up of one or a group of LEDs which can be controlled using SPI communication. This communication is often referred as a protocol, which is a data language specific to the IC chip. 

SPI pixels are commonly used in LED strips and other lighting applications where precise control over individual LEDs is desired.