LED

/ˌɛl iː ˈdiː/

n. "Semiconductor p-n junction emitting photons via electron-hole recombination unlike incandescent filaments."

LED, short for Light Emitting Diode, forward-biases GaN/AlGaInP junction dropping 2.8-3.4V while radiating 450-470nm blue light—phosphor conversion creates white CCT 2700-6500K as Stokes shift down-converts 30% energy to yellow filling spectrum gap. Contrasts OLED organic emissive layers by leveraging III-V epitaxy achieving 200lm/W efficacy; PWM dimming at 1-10kHz modulates 0-100% without color shift.

Key Characteristics: Forward Voltage 2.7-3.4V blue/white; 1.8V red; thermal runaway above 85°C Tjmax. - Luminous Efficacy 150-220lm/W white; CRI 70-95 via phosphor tuning LuAG/YAG. - Thermal Resistance 2-10K/W junction-to-case; 50mA/chip max derated 0.5mA/°C. - Beam Angle 110-140° Lambertian; secondary optics collimate to 15° spot. - Lifespan L70 50,000hrs @0.8xIf; droop above 150lm/W due to Auger recombination.

// WS2812B LED strip driver (RGB, single-wire protocol)
// 800kHz bit-banged timing, 50µs reset

#define LED_PIN   GPIO_PIN_0
#define LED_COUNT 24
#define T0H  0.4f  // 0 bit high time (us)
#define T1H  0.85f // 1 bit high time  
#define T0L  0.85f // 0 bit low time
#define T1L  0.45f // 1 bit low time
#define RESET_US 50

typedef struct {
    uint8_t r,g,b;
} rgb_t;

void ws2812_send(rgb_t* pixels, int count) {
    for(int i=0; i<count; i++) {
        uint32_t bits = (pixels[i].g<<16) | (pixels[i].r<<8) | pixels[i].b;
        for(int b=23; b>=0; b--) {
            if(bits & (1<<b)) {
                GPIO_WritePin(LED_PIN, 1);  delay_us(T1H);
                GPIO_WritePin(LED_PIN, 0);  delay_us(T1L);
            } else {
                GPIO_WritePin(LED_PIN, 1);  delay_us(T0H);
                GPIO_WritePin(LED_PIN, 0);  delay_us(T0L);
            }
        }
    }
    delay_us(RESET_US);  // Latch
}

Conceptually, LED replaces filament waste with direct band-gap recombination—blue die + yellow phosphor creates white spanning 2000-10000K while SerDes LVDS streams pixel data to TLC drivers. Micro-LED 10µm pitch targets AR glasses where PAM4 backplanes feed 16K displays; contrasts ENIG PCB gold by riding HASL solder for cost while COB packages dump 1kW/m² into Bluetooth mesh-lit smart factories.