How to convert 1 lux to 1 lumen/m²?

1 lux = 1 lumen per square meter

How to convert 1 candela to 1 lumen/steradian?

1 candela = 1 lumen per steradian

What is the difference between luminance and illuminance?

Illuminance is the amount of light falling on a surface, measured in lux or foot-candles. Luminance is the light reflected or emitted from a surface, which is what we perceive as brightness, measured in cd/m². For more details, explore our Luminance Converter.

How do you convert Lux to Foot-candles?

To convert Lux to Foot-candles, divide the value in Lux by 10.764. The formula is: fc = lx / 10.764. One foot-candle is the illuminance on a one-square-foot surface from a one-candela source one foot away. Find more conversion guides in our Units Guide.

What are Lumens and how do they relate to Lux?

Lumens measure the total light output of a source, while Lux measures the light intensity on a surface. The relationship is: Lux = Lumens ÷ Area (in square meters). For example, a 1000 lumen bulb will produce 1000 lux over a 1 square meter area.

What does Candela (cd) measure?

Candela measures luminous intensity, which is the amount of light emitted in a specific direction. It's commonly used for directional light sources like spotlights and LED lights. For detailed conversions, see our Luminous Intensity Converter.

What are typical recommended light levels for an office?

For general office work, a lighting level of around 500 lux is commonly recommended to ensure comfort and prevent eye strain. This can be measured with a light meter or estimated using our conversion tools.

Is this light converter accurate?

Yes, this tool uses official photometric conversion factors for accurate results and is completely free to use. All conversions follow international standards and are regularly updated for precision.

Illuminance Levels

Sunlight

≈ 100,000 lux (direct sunlight)

Office Lighting

≈ 500 lux (typical office)

Home Lighting

≈ 200 lux (living room)

Moonlight

≈ 0.25 lux (full moon)

Photometry Applications

Architectural Lighting

Illuminance calculations for building design

Photography

Light intensity and luminance measurements

Display Technology

Screen brightness and candela measurements

Safety Standards

Workplace and road lighting requirements

About Light & Photometry Measurement

Photometry is the science of measuring visible light in terms of its perceived brightness to the human eye. Unlike radiometry which measures all electromagnetic radiation, photometry is weighted by the luminosity function that accounts for human visual sensitivity. These measurements are crucial in lighting design, display technology, and safety applications across various industries.

What is Light and Photometry?

Light is electromagnetic radiation that is visible to the human eye, typically in the wavelength range of 380-780 nanometers. Photometry specifically measures light as perceived by human vision, taking into account the eye's sensitivity to different wavelengths. The fundamental principle is that photometric measurements are weighted by the luminosity function V(λ), which peaks at 555 nm (green light) where the human eye is most sensitive.

The relationship between radiometric and photometric quantities is given by the luminous efficacy formula:

Φ_v = K_m × ∫ V(λ) × Φ_e(λ) dλ

Where: Φ_v = luminous flux, K_m = maximum luminous efficacy (683 lm/W), V(λ) = luminosity function, Φ_e(λ) = spectral radiant flux

Common Photometric Units and Conversions

Quantity	SI Unit	Symbol	Common Units	Conversion
Luminous Flux	Lumen	lm	Candela-steradian	1 lm = 1 cd·sr
Illuminance	Lux	lx	Foot-candle, Phot	1 lx = 0.0929 fc
Luminance	Candela/m²	cd/m²	Nit, Stilb, Lambert	1 cd/m² = 1 nit
Luminous Intensity	Candela	cd	Candlepower	1 cd = 1 cp

Types of Light Measurement

Measurement Type	What it Measures	Real-World Example	Typical Values
Illuminance	Light falling on a surface	Office desk lighting	500-750 lux
Luminance	Light emitted/reflected from surface	Computer monitor brightness	100-300 cd/m²
Luminous Flux	Total light output from source	LED bulb total output	800-1600 lumens
Luminous Intensity	Light in specific direction	Flashlight beam	10,000-50,000 cd

Light Measurement Instruments

Various specialized instruments are used for accurate photometric measurements, each designed for specific applications and measurement ranges.

Lux Meters (Illuminance)

• Silicon photodiodes with V(λ) filter
• Cosine-corrected diffusers
• Range: 0.01 to 200,000 lux
• Applications: Workplace lighting, photography

Luminance Meters

• Imaging sensors with narrow field of view
• Spectral response matching human eye
• Range: 0.01 to 2,000,000 cd/m²
• Applications: Display calibration, road lighting

Integrating Spheres

• Spherical cavities with diffuse coating
• Measures total luminous flux
• High accuracy for LED testing
• Applications: Lamp testing, LED characterization

Goniophotometers

• Measures angular light distribution
• 3D light intensity mapping
• Essential for lighting design
• Applications: Automotive lighting, architectural

Light - Distance - Intensity Relationship

The fundamental relationship between light intensity and distance follows the inverse square law, which is crucial for understanding how light spreads from a point source.

E = I / d²

Where: E = illuminance (lux), I = luminous intensity (candela), d = distance (meters)

This law states that illuminance decreases with the square of the distance from the light source. For example, if you double the distance from a light source, the illuminance becomes one-fourth of the original value.

Diagram: Light Measurement Relationships

Light Source (Luminous Flux: Φ)

↓ Directional (Luminous Intensity: I)

↓ Incident on Surface (Illuminance: E)

↓ Reflected/Emitted (Luminance: L)

The photometric measurement chain: from light source to perceived brightness

Why Light Measurement is Important

Safety and Health

• Workplace lighting standards (OSHA, IES)
• Road lighting for driver safety
• Emergency lighting requirements
• Eye strain prevention in offices
• Circadian rhythm regulation

Technology and Design

• Display technology calibration
• LED efficiency optimization
• Architectural lighting design
• Photography and cinematography
• Automotive lighting regulations

Industry Standards and Regulations

Application	Standard	Required Level	Measurement Method
Office Work	IES RP-1	500-750 lux	Lux meter at work surface
Reading Areas	ANSI/IES	750-1000 lux	Horizontal illuminance
Precision Work	ISO 8995	1500-3000 lux	Task-specific measurement
Street Lighting	CIE 115	10-20 lux average	Road surface luminance

Frequently Asked Questions

How accurate are photometric measurements?

High-quality photometric instruments can achieve accuracies of ±3-5% when properly calibrated. Factors affecting accuracy include instrument calibration, environmental conditions, and proper measurement techniques.

What's the difference between lux and lumens?

Lumens measure total light output from a source, while lux measures light intensity on a surface. Lux = Lumens ÷ Area (in square meters). A 1000-lumen bulb produces 1000 lux over 1 square meter.

How do I choose the right light meter?

Consider your measurement range, accuracy requirements, and application. For general lighting, a lux meter with cosine correction is sufficient. For displays, use a luminance meter with narrow field of view.

Why is human eye sensitivity important?

The human eye is most sensitive to green light (555 nm) and less sensitive to red and blue. Photometric measurements use the V(λ) function to weight light according to human perception, making them more relevant than raw radiometric measurements.

Key Takeaway

Photometric measurements are essential for creating optimal lighting environments that balance human comfort, energy efficiency, and safety. Understanding the relationships between different photometric quantities enables proper lighting design and evaluation across various applications.

Light & Photometry Converter