Star Luminosity Calculator
Luminosity of a star in solar units and watts, its peak colour, absolute magnitude and the flux reaching us.
Results
Luminosity
1.000000
L☉
Power
3.828e+26
W
Wavelength
502.04
nm
Absolute magnitude
4.8300
Flux received
0.000000018873
W/m²
What this tool does
Two things set how much light a star pours out: how big it is and how hot. Temperature dominates because it enters to the fourth power — a star only twice as hot as the Sun shines sixteen times brighter at the same size. That is why a red giant a hundred times the Sun's radius can still be outshone by a small blue star.
Formula
L ÷ L☉ = (R ÷ R☉)² × (T ÷ T☉)⁴
Variables
| Symbol | Meaning | Unit |
|---|---|---|
r | Radius | R☉ |
t | Surface temperature | K |
d | Distance | ly |
L | Luminosity | L☉ |
LW | Power | W |
WL | Wavelength | nm |
AM | Absolute magnitude | — |
FL | Flux received | W/m² |
Worked example
- Radius1 R☉
- Surface temperature5772 K
- Distance4.2465 ly
- Luminosity1.000000 L☉
- Power3.828e+26 W
- Wavelength502.04 nm
- Absolute magnitude4.8300
- Flux received0.000000018873 W/m²
Limitations
- The formula assumes ideal conditions: no friction losses, no air resistance and no efficiency losses unless you enter them.
- The default values are typical reference figures, not measurements of your situation. Replace them with your own data whenever you have it.