Irradiance and Illuminance Calculator

1. What is the Irradiance and Illuminance Calculator?

Definition: This calculator determines irradiance (radiometric flux per unit area) and illuminance (photometric flux per unit area) based on luminous intensity and distance.

Purpose: It is used in lighting design, photography, and photometry to assess light distribution and intensity.

2. How Does the Calculator Work?

The calculator uses the following relationships: \[ E = \frac{I}{d^2} \] \[ E_v = \frac{I}{d^2} \] Where:

\(E\): Irradiance (W/m²)
\(E_v\): Illuminance (lux or foot-candles)
\(I\): Luminous intensity (cd)
\(d\): Distance (m)

Unit Conversions:

Distance: m, ft (1 ft = 0.3048 m)
Illuminance: lux, fc (1 lux = 0.0929030436 fc)

Steps:

Enter the luminous intensity (I) in candela (cd).
Enter the distance (d) and select its unit.
Click "Calculate" to determine irradiance (W/m²) and illuminance.
Select the desired unit for illuminance (lux or fc).

3. Importance of Irradiance and Illuminance

Understanding these measures is crucial for:

Lighting Design: Ensuring adequate light levels for visibility.
Photography: Adjusting exposure based on light intensity.
Safety: Assessing light exposure for human comfort.

4. Using the Calculator

Examples:

Example 1: Luminous intensity = 1 cd at 1 m:
- \(E = 1 / 1^2 = 1 \, \text{W/m}^2\)
- \(E_v = 1 / 1^2 = 1 \, \text{lux} \approx 0.0929 \, \text{fc}\)
Example 2: Luminous intensity = 1 cd at 1 ft (0.3048 m):
- \(E = 1 / (0.3048)^2 \approx 10.76 \, \text{W/m}^2\)
- \(E_v = 1 / (0.3048)^2 \approx 10.76 \, \text{lux} \approx 1 \, \text{fc}\)

5. Frequently Asked Questions (FAQ)

Q: What is the difference between irradiance and illuminance?
A: Irradiance measures radiometric flux (all wavelengths), while illuminance measures photometric flux (visible light only).

Q: Why does intensity decrease with distance?
A: Light spreads over a larger area as distance increases, reducing flux density.