Measure light strength using practical engineering formulas. Switch between flux, illuminance, angle, and distance modes. View exports, examples, and graphs for faster lighting evaluation.
The graph shows predicted illuminance change with distance using the calculated or entered luminous intensity and incidence angle.
| Case | Flux (lm) | Beam Angle (deg) | Distance (m) | Incidence Angle (deg) | Intensity (cd) | Illuminance (lux) |
|---|---|---|---|---|---|---|
| Spotlight A | 1200 | 30 | 1 | 0 | 5605.05 | 5605.05 |
| Floodlight B | 2400 | 60 | 2 | 0 | 2853.86 | 713.47 |
| Test Bench C | — | — | 2 | 20 | 2128.36 | 500.00 |
| Display LED D | — | — | 3 | 15 | 1000.00 | 107.29 |
1. Luminous intensity from flux and solid angleI = Φ / Ω
2. Solid angle of a conical beamΩ = 2π(1 - cos(θ / 2))
3. Illuminance from intensity, distance, and angleE = (I × cos α) / r²
4. Intensity from illuminance, distance, and angleI = (E × r²) / cos α
Where
Luminous intensity measures visible light emitted in a specific direction. It uses candela and helps compare how concentrated a lamp, LED, or optical beam appears along its main axis.
Lumens describe total visible light output. Candela describes directional strength. A source can have the same lumen value as another source but much higher candela when its light is concentrated into a narrow beam.
Beam angle changes how the same luminous flux spreads through space. Narrow beams use smaller solid angles, so intensity rises. Wide beams spread light more broadly, reducing candela.
Illuminance follows the inverse square relationship for point-like sources. When distance doubles, the same directional light spreads over four times the area, so lux falls to one quarter.
Incidence angle adjusts illuminance through the cosine factor. As the surface tilts away from the beam, the same light covers a larger apparent area, lowering measured lux.
Use solid angle when optical data already comes from photometric files, narrow-beam calculations, or measured angular distributions. Use beam angle when a conical approximation is acceptable and easier to interpret.
It works best for point-source or simplified directional models. Complex fixtures with asymmetric optics, multiple emitters, or reflector losses may need full photometric files and more detailed lighting software.
Yes. The CSV is useful for spreadsheets and documentation. The PDF output gives a quick summary for design reviews, technical notes, classroom work, and internal engineering comparisons.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.