Calculate the required heatsink thermal resistance for any LED or LED array. Uses the full junction-to-ambient thermal resistance chain (Rth_jc + Rth_cs + Rth_sa) to find the minimum heatsink size, estimate physical dimensions, and predict junction temperature and L70 lifespan at any ambient temperature.
LED package — quick presets
High-power SMD
Tj_max 125°C, Rth_jc 3.5
COB module
Tj_max 150°C, Rth_jc 1.5
Cree XP-G3
Tj_max 125°C, Rth_jc 8.0
Lumileds LUXEON
Tj_max 135°C, Rth_jc 4.0
COB 50W chip
Tj_max 150°C, Rth_jc 0.8
Custom
enter below
LED thermal specification
From LED datasheet — absolute maximum
From LED datasheet — junction to solder point
Fraction of input power leaving as light (typical 35-55%)
Thermal interface material (TIM)
Target Tj — typically Tj_max – 25°C safety margin
Please fill in LED thermal specifications.
Required heatsink thermal resistance
0 °C/W
0°C
Junction temp
0W
Heat dissipated
0cm²
Min heatsink area
0k hrs
Est. L70 lifespan
Junction temperature within target
Thermal resistance chain — junction to ambient
Temperature profile — junction to ambient
Performance at different ambient temperatures — same heatsink
AmbientJunction TSafety marginL70 lifespanStatus
LED thermal management tips
LED input power
Heat dissipated (Pd)
Thermal resistance chain
Required Rth_sa
Achieved junction temp
Safety margin to Tj_max
Estimated L70 lifespan
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