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Every LED article on this site talks about volts, amps, and ohms. If those terms are fuzzy, start here. This is the minimum electrical theory you need to choose the right components and understand why they work together.
The Three Basics
Electricity has three fundamental quantities. You only need to understand how they relate to each other.
| Quantity | Symbol | Unit | What It Means |
|---|---|---|---|
| Voltage (V) | V | Volts (V) | The pressure pushing current through a circuit. Higher voltage = more push. |
| Current (I) | I | Amps (A) | The flow of electricity through the circuit. More current = more flow. |
| Resistance (R) | R | Ohms (Ω) | How much the circuit resists the flow. Higher resistance = less current for a given voltage. |
The classic analogy: voltage is water pressure, current is the flow rate, and resistance is the pipe diameter. A narrow pipe (high resistance) restricts flow even at high pressure.
Ohm’s Law: The One Formula
These three quantities are locked together by Ohm’s Law:
V = I × R
Rearranged:
- I = V / R (current equals voltage divided by resistance)
- R = V / I (resistance equals voltage divided by current)
If you know any two, you can calculate the third. This relationship governs every circuit, including LED circuits.
Why This Matters for LEDs
A typical white LED has a Forward Voltage of about 3.0 V and is rated for 350 mA. Using Ohm’s law, the effective resistance at that operating point is:
R = 3.0V / 0.35A = 8.6 ohms
But here’s the problem: an LED’s resistance is not fixed. It varies with temperature and changes steeply with voltage. A small increase in voltage causes a large increase in current. This is why you can’t just connect a voltage source to an LED and set the voltage to 3.0 V; the current will be uncontrolled.
This is the core reason LEDs require constant-current drivers rather than constant-voltage supplies. The driver holds the current fixed regardless of how the LED’s resistance shifts.
Power: Volts Times Amps
There’s one more quantity you’ll see throughout our product specs:
P = V × I
Power (measured in watts) tells you how much energy the LED converts into light and heat. A module running at 3.0 V and 700 mA consumes:
3.0 × 0.7 = 2.1 watts per LED
A Tri-Star module with 3 LEDs in series consumes roughly 6.3 watts. That wattage determines how much heatsinking you need; every watt that doesn’t become light becomes heat.
What These Numbers Mean in Practice
Voltage (V): What Your Power Supply Provides
Your power supply delivers a voltage. Your driver converts that into regulated current for the LEDs. The supply voltage must be high enough to cover the total Forward Voltage of your LED string plus the driver’s overhead.
- Single white LED: ~3.0–3.5 V Forward Voltage
- Tri-Star module (3 LEDs in series): ~9.0–10.5 V total
- Driver overhead: 2.0–2.5 V (varies by driver model)
A 12V supply can drive 1–2 white LEDs through a BuckPuck. A 24 V supply can handle 6. See what voltage is needed to power LED Modules with a BuckPuck or PowerPuck driver? for the exact formula.
Current (mA): What Determines LED Brightness
Current is what makes the LED produce light. More current = more light (up to the rated maximum). Our modules are typically rated at either 350 mA or 700 mA.
- 350 mA: Standard drive current. Good balance of brightness and thermal load.
- 700 mA: High output. Roughly 70–80% more light than 350 mA (not double, diminishing returns). Requires better heatsinking.
The driver’s job is to hold the current at exactly the rated value. This is why our product pages specify drive current, not voltage; current is the variable that matters.
Resistance (Ω): Why You Can’t Just Use a Resistor
You might think: if the LED needs 350 mA, calculate the right resistor and use a voltage supply. This technically works but wastes power as heat in the resistor and provides no protection against voltage fluctuations or temperature changes.
A resistor sets the current based on the voltage difference across it. If the supply voltage drifts up by 0.5 V, the current to the LED increases. If the LED heats up and its Forward Voltage drops, the current increases further. With high-power LEDs consuming watts (not milliwatts), these fluctuations matter.
Current-regulating drivers solve this by actively adjusting their output to maintain constant current regardless of input voltage or LED temperature changes. See Can I use a resistor instead of a current-regulating driver? for the full comparison.
Quick Reference: Electrical Specs on Our Product Pages
When you look at an LED module product page, here’s what the electrical specs mean:
| Spec | What It Tells You |
|---|---|
| Forward Voltage (Vf) | How much voltage the module needs at a given drive current. Used to calculate supply voltage requirements. |
| Drive Current | The current the module is designed to receive. Determines which driver to use. |
| Power (W) | Vf × drive current. Determines heatsink size. |
| Max Current | The absolute maximum; not a target. Driving at max current shortens lifespan and requires aggressive cooling. |
The Takeaway
You don’t need an electrical engineering degree to work with high-power LEDs. You need to know three things:
- Voltage is the pressure. Your power supply provides it.
- Current is the flow. Your driver regulates it. It determines brightness.
- LED resistance is not fixed, which is exactly why you need a driver instead of a simple voltage source.
If you can follow V = I × R and P = V × I, you can read any spec sheet on this site and understand what the numbers mean.
Related Articles
- Constant Current vs Constant Voltage: What Your LEDs Need and Why
- How do I power high-power LED modules?
- How do I determine the wattage of an LED module?
- Can I use a resistor instead of a current-regulating driver?
- Series vs Parallel: How to Wire Multiple LED Modules
- What voltage is needed to power LED Modules with a BuckPuck or PowerPuck driver?
- LED Driver Selection Guide: BuckPuck vs PowerPuck vs BoostPuck
