Light Distance Calculator
Estimate the illuminance (lux) at a given distance from a light source using the inverse square law.
Understanding Light Intensity and Distance
When planning lighting for homes, offices, outdoor areas, or industrial spaces, it’s essential to understand how light behaves over distance. This calculator uses the inverse square law to estimate how much illuminance (measured in lux) reaches a surface from a given light source based on its lumen output and the distance from the source.
What Is Illuminance (Lux)?
Illuminance refers to the amount of light that lands on a surface. It is measured in lux (lx), which is equivalent to lumens per square meter. One lux equals one lumen per square meter. This measurement is critical in lighting design, especially for ensuring adequate brightness for tasks, comfort, and safety.
The Inverse Square Law
Light intensity diminishes rapidly with distance, and this effect follows a simple physical rule known as the inverse square law. According to this law, illuminance is inversely proportional to the square of the distance from the light source.
Illuminance (lux) = Lumens ÷ (4 × π × Distance²)
Example
Suppose you have an 800-lumen LED bulb and want to know how much light reaches a surface 2 meters away:
- Distance² = 2² = 4
- 4 × π × 4 ≈ 50.27
- Illuminance = 800 ÷ 50.27 ≈ 15.91 lux
Why Distance Matters in Lighting Design
- Task Lighting: Too little lux at work surfaces can cause eye strain or reduce productivity.
- Safety: Insufficient lighting in stairwells or walkways increases risk of accidents.
- Energy Efficiency: Avoid over-lighting distant surfaces by properly aiming fixtures or using reflective surfaces.
Target Lux Levels for Various Environments
| Area | Recommended Lux |
|---|---|
| Living Room | 100–300 lx |
| Office Desk | 300–500 lx |
| Kitchen Counter | 500–1000 lx |
| Warehouse | 200–750 lx |
| Reading/Study Area | 500 lx |
| Corridors/Hallways | 50–100 lx |
Tips for Optimizing Light Distribution
- Use focused beam angles for long-distance coverage.
- Combine ambient and task lighting to reduce shadows.
- Use reflectors or diffusers to spread light evenly.
- Keep light sources clean and free of dust buildup.
Frequently Asked Questions
Does this calculator account for beam angle?
No. This version assumes an omnidirectional light spread. For beam-specific lux, use our candela/lux tools.
How accurate is the inverse square law?
It's a good approximation for point sources in open space. Real-world fixtures may vary due to shape, reflector design, or light loss.
What if I double the distance?
Illuminance decreases by a factor of 4. At 4x the distance, it decreases by 16x.
Can I use this calculator for outdoor lighting?
Yes, especially when estimating light coverage from floodlights or streetlights over varying distances.
Does surface color affect lux?
This calculator only measures incident light. Dark or reflective surfaces may absorb or reflect lux differently but won’t affect the calculated incident value.
How do I increase lux at a distance?
- Increase the lumen output.
- Reduce the distance.
- Use optics to concentrate the beam (narrower angle).