Power LED Thermal Calculator
LED junction temperature from drive power and the star/heatsink chain — with lumen droop and lifetime band shown.
Heat is the #1 LED killer: phosphor degrades and the dome yellows long before the die dies. Unlike most parts, LED Vf DROPS as it heats (≈ −2 mV/°C/junction) — on a constant-voltage supply current then rises, heating it further: always drive power LEDs from constant CURRENT. Aluminium-core PCB (MCPCB) is non-negotiable above ~1 W.
LED Thermal Calculator computes power-LED junction temperature, lumen droop and lifetime band — free, instant and private in your browser. Lighting modders, growers and product designers running LEDs at real power use it to skip the datasheet algebra: type your numbers, read the answer with the substituted formula shown step by step, and share an exact permalink of the calculation.
About Power LED Thermal Calculator
LED Thermal Calculator computes power-LED junction temperature, lumen droop and lifetime band using the standard engineering relation: Tj = Ta + Vf·If·(1−η(optical))·Σθ; flux derates ~0.3 %/°C. Worked live: a 2 W emitter on a star with a modest sink lands around 80 °C — about 16 % dimmer than its 25 °C rating. The result recalculates on every keystroke, the worked-example panel shows your numbers substituted into the formula, and the Copy permalink button encodes the inputs in the URL so a colleague opens exactly your calculation. Everything runs client-side — nothing you type leaves your device.
How to use Power LED Thermal Calculator
- 1Enter your values — the tool starts with realistic defaults for this exact use case, so the worked example is meaningful immediately.
- 2Read the live result and the worked-example panel, which substitutes your numbers into the formula step by step.
- 3Adjust any input to compare scenarios, then use Copy result or Copy permalink to share the calculation.
Why use Power LED Thermal Calculator?
- ✓Implements the real formula — Tj = Ta + Vf·If·(1−η(optical))·Σθ — with the substitution shown, not a black box
- ✓Built for lighting modders, growers and product designers running LEDs at real power
- ✓Copy result and permalink buttons — share the exact calculation in a README, forum answer or design review
- ✓100% free, no sign-up, runs entirely in your browser (works offline once loaded)
Frequently asked questions
How do you calculate led thermal?+
Power-LED junction temperature, lumen droop and lifetime band follows Tj = Ta + Vf·If·(1−η(optical))·Σθ; flux derates ~0.3 %/°C. For example, a 2 W emitter on a star with a modest sink lands around 80 °C — about 16 % dimmer than its 25 °C rating. The calculator applies the same relation and shows the substituted arithmetic so you can verify every step.
Why constant-current drive for power LEDs?+
Vf falls ~2 mV/°C per junction as the LED warms; on a constant-voltage source the current then climbs, heating it further — a runaway loop. Constant-current drivers break the loop and define brightness regardless of temperature and part spread.
What does L70 mean on LED datasheets?+
Hours until output falls to 70 % of initial — the standard lifetime metric (LEDs dim, they rarely die abruptly). It's quoted AT a junction temperature: the same emitter might be L70 = 60 000 h at 85 °C but 15 000 h at 125 °C. Cooling buys lifespan directly.
Is the LED Thermal Calculator free and private?+
Yes — completely free with no sign-up or usage limits, and it runs entirely in your browser: the values you enter are never uploaded or stored on a server.
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