Watts to Lux Calculator

Power (P):

Light Source:

Surface Area (A): m²

Luminous Flux (lm): Illuminance (lx):

1. What is a Watts to Lux Calculator?

Definition: This calculator computes the illuminance in lux (lx) by converting electrical power in watts (W) to luminous flux in lumens (lm) using the luminous efficacy of a light source, then dividing by the surface area.

Purpose: It is used to estimate the brightness (illuminance) of a light source on a surface, helping in lighting design for homes, offices, or outdoor spaces.

2. How Does the Calculator Work?

The illuminance is calculated using:

\( \text{Luminous Flux (lm)} = P(\text{W}) \times \text{Luminous Efficacy (lm/W)} \)
\( \text{Illuminance (lx)} = \frac{\text{Luminous Flux (lm)}}{\text{Surface Area (m}^2\text{)}} \)

Where:

\( P(\text{W}) \) is the power in watts (W)
\( \text{Luminous Efficacy (lm/W)} \) is the efficiency of the light source in lumens per watt
\( \text{Surface Area (m}^2\text{)} \) is the area illuminated

Steps:

Enter the power (\( P \)) and select a unit (mW, W, kW, MW, GW)
Select the light source or enter a custom luminous efficacy (lm/W)
Enter the surface area in square meters (m²)
Convert power to W
Calculate luminous flux using \( \text{Luminous Flux} = P \times \text{Luminous Efficacy} \)
Calculate illuminance using \( \text{Illuminance} = \text{Luminous Flux} / \text{Area} \)

Display format:

If a value is > 10000 or < 0.0001 (and not zero), use scientific notation (e.g., \( 1.23456e-3 \))
Otherwise, display with 5 decimal places

3. Importance of Watts to Lux Calculation

Details: This calculation helps determine the brightness of a light source on a surface, which is crucial for designing lighting systems that meet specific illumination requirements, such as in offices, homes, or public spaces.

4. Using the Calculator

Tips: Ensure all inputs are positive. Select the appropriate light source to use its typical luminous efficacy, or enter a custom value if known. The surface area should represent the area directly illuminated by the light source.

Examples:

Example from Image: \( P = 10 \, \text{W} \), Light Source = Mercury Vapor (35-65 lm/W, average 50 lm/W), Area = 1 \, \text{m}^2 \):
- \( \text{Luminous Flux} = 10 \times 50 = 500.00000 \, \text{lm} \)
- \( \text{Illuminance} = 500 / 1 = 500.00000 \, \text{lx} \)
LED Bulb in a Room: \( P = 15 \, \text{W} \), Light Source = LED Bulbs (80-120 lm/W, average 100 lm/W), Area = 10 \, \text{m}^2 \):
- \( \text{Luminous Flux} = 15 \times 100 = 1500.00000 \, \text{lm} \)
- \( \text{Illuminance} = 1500 / 10 = 150.00000 \, \text{lx} \)
Custom Efficacy: \( P = 100 \, \text{W} \), Luminous Efficacy = 90 \, \text{lm/W}, Area = 5 \, \text{m}^2 \):
- \( \text{Luminous Flux} = 100 \times 90 = 9000.00000 \, \text{lm} \)
- \( \text{Illuminance} = 9000 / 5 = 1800.00000 \, \text{lx} \)

5. Frequently Asked Questions (FAQ)

Q: What is lux?
A: Lux (lx) is a unit of illuminance, measuring the amount of light (luminous flux) per unit area, in lumens per square meter (lm/m²).

Q: What is luminous efficacy?
A: Luminous efficacy measures how efficiently a light source converts electrical power into visible light, expressed in lumens per watt (lm/W).

Q: Why does the light source matter?
A: Different light sources have different luminous efficacies, affecting how much light they produce per watt of power. For example, LED bulbs are more efficient than incandescent bulbs.

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