LED brightness control in Raspberry Pi

Introduction

We control LED brightness to make lights dimmer or brighter smoothly. This helps save energy and create nice lighting effects.

When you want to make a night light that gets dimmer over time.

To create mood lighting that changes brightness slowly.

When building a project that needs different light levels, like a lamp.

To show visual feedback by changing LED brightness based on sensor input.

Syntax

Raspberry Pi

import RPi.GPIO as GPIO
import time

led_pin = 18
frequency = 1000
duty_cycle = 50

GPIO.setmode(GPIO.BCM)
GPIO.setup(led_pin, GPIO.OUT)
pwm = GPIO.PWM(led_pin, frequency)
pwm.start(duty_cycle)

Use GPIO.PWM(pin, frequency) to create a PWM object controlling the LED.

duty_cycle is a number from 0 (off) to 100 (fully on) controlling brightness.

Examples

This sets up an LED on pin 18 with half brightness.

Raspberry Pi

import RPi.GPIO as GPIO

GPIO.setmode(GPIO.BCM)
GPIO.setup(18, GPIO.OUT)
pwm = GPIO.PWM(18, 1000)  # 1000 Hz frequency
pwm.start(50)  # 50% brightness

Use ChangeDutyCycle to change LED brightness while running.

Raspberry Pi

pwm.ChangeDutyCycle(75)  # Change brightness to 75%

Stop PWM and clean up GPIO pins when done.

Raspberry Pi

pwm.stop()
GPIO.cleanup()

Sample Program

This program slowly increases LED brightness from 0% to 100%, then back down to 0%, printing the brightness level each step.

Raspberry Pi

import RPi.GPIO as GPIO
import time

led_pin = 18
GPIO.setmode(GPIO.BCM)
GPIO.setup(led_pin, GPIO.OUT)

pwm = GPIO.PWM(led_pin, 1000)  # 1000 Hz frequency
pwm.start(0)  # start with LED off

try:
    for brightness in range(0, 101, 10):
        pwm.ChangeDutyCycle(brightness)
        print(f"LED brightness: {brightness}%")
        time.sleep(0.5)
    for brightness in range(100, -1, -10):
        pwm.ChangeDutyCycle(brightness)
        print(f"LED brightness: {brightness}%")
        time.sleep(0.5)
finally:
    pwm.stop()
    GPIO.cleanup()

Important Notes

Make sure to connect the LED with a resistor to avoid damage.

Use GPIO.cleanup() to reset pins after your program ends.

Frequency controls how fast the LED turns on and off; 1000 Hz is smooth for eyes.

Summary

LED brightness is controlled by changing PWM duty cycle from 0 to 100%.

Use RPi.GPIO library to set up PWM on Raspberry Pi pins.

Always clean up GPIO pins after use to avoid issues.