Build Your Own
LED Flashlight
Choose components, understand the tradeoffs, and create a working digital flashlight. Your decisions shape the final artifact.
Meet the Components
Every flashlight is a story of electrons seeking ground. Before we build, let's understand what we're working with.
Our flashlight needs five components: a battery (the source), an LED (the light), a resistor (the sacrifice), a reflector (the shaper), and a switch (the gate).
Each choice you make will ripple through the system. Choose a blue LED? You'll need more voltage. Pick a tiny coin cell? Runtime shrinks. There are no wrong answers—only tradeoffs.
The digital twin above updates in real-time as you make choices. Watch how components appear and metrics change.
Choose Your Light
The LED is the heart of your flashlight. Each color isn't just aesthetics—it's physics. The forward voltage tells you the minimum voltage needed to make it glow.
Red LEDs are easy to drive (2.0V), while white and blue demand more (3.2V). Your battery choice later will need to meet or exceed this voltage.
Green LEDs appear brightest to human eyes—our sensitivity peaks around 555nm. The "color factor" adjusts perceived brightness accordingly.
Power Source
Your Green LED needs at least 2.2V to light up. Choose a battery that can deliver.
More voltage gives you headroom for the resistor to work. More capacity (mAh) means longer runtime. But more batteries means more weight.
The Sacrifice
Here's the cruel truth: LEDs are greedy. Given unlimited current, they'd consume everything and burn out instantly.
The resistor is the sacrifice. It absorbs excess voltage as heat, limiting current to a safe level. This is Ohm's Law in action: I = (V_source - V_led) / R.
Lower resistance → more current → brighter light → shorter battery life (and risk of burning the LED).
The ideal resistor for 20mA (typical LED brightness) with your current setup is ~40Ω. Experiment with values above and below to see the effect.
The Tradeoff Triangle
Engineering is about tradeoffs. You can't maximize everything. This triangle shows where your current configuration lands.
You've prioritized runtime. Perfect for emergencies or camping where brightness matters less.
Shaping the Beam
LEDs emit light in a wide cone. The reflector focuses that cone into a useful beam. Tighter beams throw farther but illuminate less area.
A smooth parabolic reflector creates a tight "hotspot" for distance. Orange peel texture smooths the beam for close-up work.
Control
The switch is your interface—how you command the light. Position affects ergonomics. Type affects behavior.
Tail switches enable tactical "cigar grip" operation. Side switches work well for everyday use. Twist-heads are waterproof but slower to operate.
Test & Diagnose
Your circuit is complete. Time to flip the switch and see if your choices work together.
Your Flashlight
You've built something real—a configuration that reflects your priorities. Export it, share it, or start over and explore different tradeoffs.
The Marathon Runner
You applied Ohm's Law (V=IR) to calculate the resistor needed for your LED.
You discovered the fundamental tradeoff between brightness and battery life.
You experienced how component choices cascade — the LED voltage determines which batteries work, which determines the resistor needed.