Illuminance Conversion Calculator

The Ultimate Guide to Illumination Conversions

Illuminance is a measure of the total amount of visible light that falls upon a given surface area. It's a critical concept in lighting design, photography, horticulture, and occupational health, as it quantifies how "bright" a surface appears to the human eye. While the concept is straightforward, the units used to measure it—primarily lux and foot-candles—can be a source of confusion. Our Illumination Conversion Calculator is a simple yet powerful tool designed to help you convert between these two units instantly and accurately.

How to Use the Illumination Converter

Our tool is built for simplicity and provides real-time results as you type.

1. Select an Input Unit: Choose either the "Lux (lx)" or the "Foot-candles (fc)" input field.
2. Enter Your Value: Type the number into the selected field.
3. View the Instant Conversion: As you type, the other input field will immediately update to show the precise equivalent illuminance.
4. Clear to Reset: To perform a new conversion, simply delete the number in an input box. The other field will clear automatically.

Understanding the Units of Illuminance

To master illuminance conversions, it's essential to understand the definition and origin of each unit.

Lux (lx): The Metric Standard

The lux is the standard unit of illuminance in the International System of Units (SI). It is defined as one lumen per square meter (1 lm/m²). A lumen is the SI unit of luminous flux, which measures the total quantity of visible light emitted by a source. Therefore, lux measures how much of that light is spread over a specific area.

• Context: A brightly lit office might be around 500 lux, while direct sunlight can be over 100,000 lux.
• Application: Lux is the universal standard for lighting specifications in architecture, engineering, and occupational safety regulations in most parts of the world.

Foot-candle (fc): The Imperial Standard

The foot-candle is the corresponding unit of illuminance in the imperial and US customary systems. It is defined as one lumen per square foot (1 lm/ft²).

• Context: Because a square meter is larger than a square foot, one foot-candle represents a more concentrated amount of light than one lux.
• Application: The foot-candle is still widely used in the United States in fields such as architecture, stage lighting, cinematography, and horticulture.

The Conversion Explained

The relationship between lux and foot-candles is directly related to the relationship between a square meter and a square foot. Since there are approximately 10.764 square feet in one square meter, the conversion factor is the same:
1 foot-candle = 10.764 lux
Our calculator uses this precise factor to ensure accurate conversions every time.

Practical Applications for Illuminance

• Workplace Safety & Ergonomics: Proper lighting is crucial for preventing eye strain and ensuring a safe work environment. Occupational health standards (like those from OSHA) often specify minimum illumination levels in foot-candles or lux for different tasks.
• Photography & Cinematography: Photographers and videographers use light meters to measure the illuminance on a subject in lux or foot-candles. This allows them to set the correct camera exposure (aperture and shutter speed) for a perfectly lit shot.
• Horticulture & Indoor Farming: The growth of plants is directly related to the amount of light they receive. Growers use light meters to ensure their crops are receiving the optimal illuminance (often measured in lux) for photosynthesis and healthy growth.
• Architecture & Interior Design: Lighting designers use illuminance calculations to ensure a space is not only functional but also has the desired mood and ambiance. A museum will require different lux levels for a hallway versus an exhibit of delicate artifacts.
• Retail: In a retail setting, higher illumination levels are used to draw attention to specific products and create an inviting atmosphere.

Frequently Asked Questions (FAQ)

What is the difference between lumens and lux?

Lumens measure luminous flux, which is the total amount of visible light emitted by a source in all directions. Lux measures illuminance, which is the amount of light that actually falls on a given surface area. One lux is equal to one lumen per square meter. In short, lumens measure the 'output' of a light source, while lux measures the 'brightness' on a surface.

How many lux is one foot-candle?

One foot-candle is equal to approximately 10.764 lux. This is because a foot-candle is one lumen per square foot, and a lux is one lumen per square meter. Since there are about 10.764 square feet in a square meter, the conversion factor is the same.

What is a good lux level for an office?

A general office environment typically requires an illuminance level between 300 and 500 lux for comfortable working conditions. Areas requiring detailed tasks, such as drafting or electronics assembly, might need higher levels, up to 750 or 1000 lux, to ensure accuracy and reduce eye strain.