Lux to Lumens Converter

Convert between lux, lumens, foot-candles, and candela with beam angle and distance support. Design room lighting, estimate energy savings switching to LED, and reference illuminance standards for any space. All calculations run instantly as you type.

1. Lux / Lumens Converter Tool

Convert between lux (illuminance) and lumens (luminous flux) using area. Enter a value in either field and the other will update automatically. Choose your area unit and adjust as needed.

2. Beam Angle Calculator

For spotlights and directional fixtures, the beam angle determines how the light is distributed. A narrow beam concentrates light into a small cone with high intensity, while a wide beam spreads it across a larger area. This calculator uses the solid angle formula to convert between lux at a distance and total lumens output.

3. Room Lighting Design Calculator

Enter your room dimensions and select a room type. The calculator determines the recommended illuminance (based on EN 12464-1 and IESNA standards) and computes the total lumens required. It then tells you how many fixtures of your chosen type to install. The use factor (CU) accounts for light lost to walls, ceiling, and floor reflections; typical values range from 0.4 to 0.7 depending on room shape and surface finishes.

4. Energy Savings Calculator

Estimate how much money you save by switching from traditional bulbs to LED. Enter the number of fixtures, current bulb wattage, replacement LED wattage, and your electricity rate. The calculator shows annual cost savings, payback period, and lifetime savings. Typical LED bulbs last 25,000-50,000 hours versus 1,000 hours for incandescent and 8,000-15,000 hours for CFL.

5. Visual Room Lighting Simulation

This canvas visualization shows a top-down view of your room with light distribution from the fixtures calculated above. Brighter areas represent higher lux values. The simulation accounts for distance falloff using the inverse square law and shows how multiple fixtures create overlapping light pools for even coverage.

6. Understanding Lux and Lumens

The confusion between lux and lumens is one of the most common questions in lighting. They measure related but different things, and understanding the distinction is important for anyone buying bulbs, designing a space, or working in lighting engineering.

Lumens - Total Light Output

Lumens (lm) measure the total quantity of visible light emitted by a source in all directions. It is a measure of luminous flux. A 60W-equivalent LED bulb typically produces about 800 lumens. The lumens rating tells you how much light the bulb generates, regardless of where that light goes. Two bulbs with the same lumen rating produce the same amount of light, even if one has a narrow spotlight beam and the other is an omnidirectional globe.

Lux - Light on a Surface

Lux (lx) measures how much luminous flux falls on a surface. One lux equals one lumen per square meter. If you spread 1000 lumens evenly over 10 m², you get 100 lux. If you concentrate those same 1000 lumens onto 1 m², you get 1000 lux. Lux is what your eyes actually perceive: a desk illuminated at 500 lux appears brighter than a corridor at 100 lux, even if the corridor has more total lumens.

An Everyday Analogy

Think of a garden hose. Lumens are like the total volume of water flowing through the hose (gallons per minute). Lux is like the water pressure hitting a surface. A sprinkler spreads the water over a wide area (low pressure per point). A nozzle concentrates it into a narrow stream (high pressure per point). Same flow, different coverage. Lighting works identically: the same lumens create different lux levels depending on how the light is distributed.

7. The Formulas Behind the Conversion

The relationship between lux and lumens depends on the geometry of light distribution. Here are the key formulas used in lighting calculations.

Uniform Area Illumination

For a surface uniformly lit by one or more fixtures:

Directional Source (Beam Angle)

For a spotlight or directional fixture with beam angle θ at distance d:

The term 2π × (1 - cos(θ/2)) gives the solid angle (in steradians) of the light cone. For a full hemisphere (θ = 180°), this equals 2π sr. For a 60° spot, it is approximately 0.842 sr.

Candela to Lumens

Candela (cd) is the SI base unit for luminous intensity, measuring light concentration in a single direction:

Foot-Candles

The foot-candle conversion factor (10.764) comes directly from the number of square feet in a square meter (10.764 ft² = 1 m²). These formulas assume a point source or far-field approximation, which holds when the measuring distance is at least five times the largest dimension of the light source. For large panel fixtures measured close up, the actual lux distribution can differ from these idealized calculations.

8. Light Source Comparison

Different light technologies produce dramatically different amounts of light per watt consumed. This table compares the major types with typical efficiency (luminous efficacy), lifespan, and cost. Data based on current market averages and the U.S. Department of Energy LED Lighting Facts.

The difference in efficacy is striking. A standard LED produces 8-12 times more light per watt than an incandescent bulb. Over a bulb's lifetime, the energy savings dwarf the higher purchase price of LEDs. A single LED replacing a 60W incandescent saves roughly 365 kWh over its 25,000-hour lifespan, worth approximately $50 at average U.S. electricity rates.

9. Illuminance Standards by Application

International lighting standards specify minimum illuminance levels for different activities and spaces. The values below are drawn from EN 12464-1 (European standard for indoor workplace lighting) and IESNA (Illuminating Engineering Society of North America) recommendations.

These values represent maintained illuminance, meaning the expected light level after accounting for lamp depreciation and surface dirt accumulation over time. New installations should produce 20-25% more than the target to account for this maintenance factor, which is why the room design calculator above includes both use and maintenance factors.

10. Color Temperature Guide

Color temperature, measured in Kelvin (K), describes the visual warmth or coolness of light. It does not affect the total lumens a source produces, but it significantly impacts how humans perceive brightness, comfort, and ambiance. Lower Kelvin values produce warm, yellowish light. Higher values produce cool, bluish-white light.

Research in circadian rhythm science shows that exposure to high color temperature light (5000K+) suppresses melatonin production and promotes alertness. This makes cool daylight excellent for workspaces during daytime hours but disruptive in the evening. Many modern LED fixtures and smart bulbs offer tunable color temperature so you can use 5000K during the day and 2700K in the evening. The American Medical Association has issued guidance recommending warm-toned residential lighting (below 3000K) in the hours before sleep.

11. Foot-Candles and Candela Explained

While lux and lumens are the internationally standardized units, two other units appear frequently in lighting specifications and building codes, especially in North America.

Foot-Candles (fc)

The foot-candle is the imperial counterpart to lux. One foot-candle equals one lumen per square foot. Since one square meter contains 10.764 square feet, one foot-candle equals 10.764 lux. North American building codes, IESNA recommendations, and the IBC (International Building Code) all specify lighting levels in foot-candles. When reading American specifications, simply multiply by 10.764 to convert to lux.

Candela (cd)

The candela is the SI base unit of luminous intensity. It measures how much light is concentrated in a particular direction. One candela is roughly equivalent to the light from a single candle (historically, this is exactly where the unit originated). The relationship between candela and lux is:

This is the inverse square law of illumination. A 1000-candela spotlight produces 1000 lux at 1 meter, 250 lux at 2 meters, and 111 lux at 3 meters. Candela is particularly useful for specifying directional sources like spotlights, flashlights, and vehicle headlights, where the total lumen output matters less than how intensely the light is focused.

Lumens and candela are related through the solid angle of emission. For an isotropic (omnidirectional) source, the total lumens equal 4π times the candela value. For a directional source with beam angle θ: Lumens = Candela × 2π × (1 - cos(θ/2)).

12. Practical Lighting Design Tips

Whether you are lighting a home renovation, a commercial office, or an outdoor space, these practical guidelines will help you achieve effective, comfortable lighting.

Layer Your Lighting

Professional lighting designers work with three layers: ambient (general room illumination), task (focused light for specific activities), and accent (decorative highlighting). A well- room has all three. The ambient layer provides 30-50% of total illumination, task lighting raises it to the required level at work surfaces, and accent lighting adds visual interest at 2-3 times the ambient level.

Account for Room Reflectance

Light-colored walls and ceilings reflect 70-80% of light, multiplying effective illumination. Dark surfaces absorb most light, requiring more fixtures for the same lux level. A room with white walls and a white ceiling can achieve the same lux with 30-40% fewer lumens than an identical room painted dark gray. This is captured by the use factor in the room design calculator above.

Ceiling Height Matters

The inverse square law means that ceiling height significantly affects the lux reaching work surfaces. A fixture at a 3-meter ceiling produces 2.25 times more lux at desk height (0.75 m working plane) than the same fixture at a 4-meter ceiling. Standard calculations assume 0.75 m working plane height. For high-bay warehouses (8-12 m ceilings), LED high-bay fixtures with narrow beam angles (60-90°) concentrate light downward to overcome the distance penalty.

Spacing and Uniformity

For even illumination, space recessed downlights at 1.0-1.5 times the mounting height apart. For example, if the ceiling is 2.7 m and the working plane is 0.75 m, the mounting height is 1.95 m, so space fixtures 2.0-2.9 m apart. A spacing-to-mounting-height ratio above 1.5 creates noticeable bright spots and shadows. The room simulation canvas above visualizes this pattern.

Dimming Saves Energy and Adds Flexibility

Installing dimmable LED fixtures with compatible drivers lets you adjust light levels throughout the day. Dimming to 50% output saves roughly 40-50% energy (LEDs are not perfectly linear). In conference rooms and living spaces, dimmability adds significant comfort and utility. Always verify that the dimmer switch is rated for LED loads; standard incandescent dimmers can cause flickering with LED drivers.

13. Unit Conversion Reference

Quick reference for all lighting unit conversions used in this tool and in the broader lighting industry.

Illuminance Units

Luminous Flux Units

Area Units

14. Browser Compatibility

This tool uses standard JavaScript and the HTML5 Canvas API. All modern browsers are fully supported.

15. Related Tools

Explore more free calculators and converters for engineering, physics, and daily use: