Luminance Converter

Convert light measurements between candela/m², lux, foot-candles, and nits. Perfect for photography, lighting design, and display calibration.

About Luminance Converter

Understanding Light Measurement

Light measurement involves several distinct but related quantities. The candela (cd), the SI base unit for luminous intensity, measures the power of light in a particular direction. From this foundation, we derive other important units: the lumen (lm) for total light output, the lux (lx) for illuminance, and various units for luminance (brightness). These measurements are crucial in lighting design, photography, display technology, and architectural planning.

Common Light Levels

Condition	Illuminance	Description
Full Sunlight	100,000 lx	Direct sun
Daylight	10,000-20,000 lx	Overcast day
Office Lighting	300-500 lx	Typical workspace
Street Lighting	10-20 lx	Night safety

Unit Categories

Luminous Intensity & Flux

Candela (cd): Light intensity
Lumen (lm): Total light output
1 lm = 1 cd × sr (steradian)
LED efficiency: 100-200 lm/W

Illuminance & Luminance

Lux (lx): Light per area
Foot-candle (fc): US unit
Nit (cd/m²): Screen brightness
1 fc = 10.764 lx

Applications

Professional Uses

Architectural lighting design
Photography and cinematography
Display calibration
Workplace safety standards
Scientific research

Display Technology

HDR displays: 1,000+ nits
OLED phones: 400-800 nits
LCD monitors: 200-350 nits
HDR TVs: up to 2,000 nits

How photometry units relate to each other

Light units can be confusing because they describe different parts of the same physical situation. Luminous flux, measured in lumens, describes the total visible light output of a source. Luminous intensity, measured in candelas, describes light output in a particular direction. Illuminance, measured in lux or foot-candles, describes how much light lands on a surface. Luminance, measured in candelas per square meter or nits, describes how bright a surface appears in a given direction.

These quantities are related, but they are not interchangeable without geometry. A lamp can produce many lumens, but the illuminance on a desk depends on distance, beam angle, reflectors, shades, and room surfaces. A screen can have high luminance in nits, but that does not tell you how many lumens the display emits into the room. The calculator is useful for unit conversion, while the lighting problem itself may still require area, angle, distance, or reflectance information.

Lux and foot-candles are both illuminance units. One foot-candle equals one lumen per square foot, and one lux equals one lumen per square meter. Because a square meter is larger than a square foot, one foot-candle equals about 10.764 lux. This conversion is common when comparing US lighting recommendations with international standards. Offices, classrooms, warehouses, galleries, hospitals, and streets may publish targets in different units even when they describe the same lighting level.

Nits and candelas per square meter are equivalent units for luminance. They are often used for display brightness, phone screens, monitors, televisions, dashboards, signs, and projection surfaces. A higher nit value can improve visibility in bright environments, but it can also increase power use and eye discomfort in dark rooms. For displays, luminance should be considered with contrast ratio, black level, glare, ambient light, and content type.

Using conversions in lighting design and display work

Lighting design starts with the task. Reading fine print, inspecting parts, walking through a corridor, filming a scene, and relaxing in a living room all need different light levels. A conversion from foot-candles to lux helps compare recommendations, but it does not decide whether the level is comfortable or suitable. Glare, uniformity, color temperature, color rendering, flicker, shadows, and user age can all affect the final design.

Distance changes illuminance quickly. For a small source that spreads light outward, illuminance often follows an inverse-square pattern: double the distance and the light on the surface falls to about one quarter, assuming the beam and environment are simple. Real fixtures are shaped by lenses, reflectors, diffusion, and room reflections, so measurements may differ. Still, the principle explains why moving a task light closer can have a much larger effect than changing the bulb by a small amount.

In photography and cinematography, light meters may report lux, foot-candles, exposure value, or camera settings. Converting between illuminance units helps match fixtures and communicate with teams that use different standards. Exposure also depends on shutter speed, aperture, ISO, lens transmission, and artistic intent. A lighting conversion gives a measurement baseline, not a complete exposure plan.

For workplace and safety decisions, use the calculator to translate units, then compare the result with the standard or guideline that applies to the space. Emergency lighting, industrial inspection, road lighting, and office lighting may have different minimums and measurement methods. If compliance matters, take readings with a calibrated meter at the required measurement height and location. A conversion is only as reliable as the measurement being converted.

Measurement context behind converted light values

A converted light value should always be tied to where and how the measurement was taken. A lux reading on a desk is not the same as a lux reading on the floor, wall, or ceiling. The sensor angle, distance from the source, and shadow from the person taking the reading can all change the number. If a conversion will be used for compliance or design, record the measurement position along with the unit.

Reflectance changes perceived brightness even when illuminance is the same. A white wall under 300 lux looks much brighter than a dark wall under the same 300 lux because the white surface reflects more light toward the viewer. Luminance captures the brightness of the surface itself, while illuminance captures light arriving at the surface. This distinction matters in galleries, offices, roadways, and display evaluation.

Beam angle can make lumen ratings misleading. Two lamps with the same lumen output can create very different lux readings if one spreads light widely and the other concentrates it into a narrow beam. Task lights, spotlights, floodlights, and downlights should therefore be compared by both total output and delivered light on the working plane. The calculator converts units, but fixture photometry explains distribution.

Color temperature and color rendering do not change a basic lux-to-foot-candle conversion, but they affect comfort and usefulness. A space can meet a numeric light level and still feel harsh, dull, or poor for color judgment. Retail, healthcare, art, food service, and photography often need attention to color quality in addition to light quantity.

Outdoor lighting adds glare and adaptation concerns. A high-luminance sign may be readable in daylight but uncomfortable at night. Roadway and security lighting need enough visibility without shining into drivers' eyes or neighboring windows. Converted units help compare specifications, but aiming, shielding, mounting height, and dimming schedules determine whether the installation works well.

Display measurements need stable settings. A phone or monitor can change luminance with auto-brightness, battery saver mode, HDR content, calibration profile, or thermal limits. When comparing nit values, use a consistent test pattern and brightness setting. Peak HDR brightness may last only briefly, while sustained full-screen brightness may be much lower.

For safety and standards work, use calibrated meters and current requirements. A phone sensor can be useful for rough checks, but it may not be accurate enough for workplace, roadway, emergency, or laboratory decisions. The calculator can translate the meter reading into the required unit, but the quality of the result depends on the quality of the measurement.

Common conversion traps in light measurement

Do not convert lumens directly to lux without area or beam information. Lumens describe total output, while lux describes light arriving on a surface. The same lamp can create high lux on a small spot or low lux across a wide area depending on optics and distance.

Do not treat nits as a room lighting value. Nits describe luminance of a surface, such as a screen or sign. Lux and foot-candles describe illuminance on a surface. A monitor with high nits can still sit in a dim room, and a bright room can contain a low-luminance display.

Be careful with manufacturer specifications. A bulb package may list lumens, a lighting plan may list lux, a photographer may use foot-candles, and a display review may list nits. These values can all be correct while describing different parts of the lighting system.

Measurement angle matters for luminance. Glossy surfaces can reflect a bright source toward the meter or viewer, creating a much higher reading from one direction than another. Matte surfaces scatter light more evenly. Record the geometry when comparing readings.

If the conversion is used for a purchase, leave a margin. Lamps age, lenses get dirty, walls change reflectance, and displays dim over time. A design that barely reaches the target on day one may fall short later. The calculator provides the unit math, while the margin handles real use.

Final light measurement check

Keep the measurement type clear before converting. Lumens describe source output, lux and foot-candles describe light on a surface, and nits describe surface brightness. If the unit describes a different part of the lighting setup, conversion alone will not answer the design question.

One more conversion check

If a specification lacks area, distance, beam angle, or surface brightness context, keep the converted value labeled as a unit conversion only. Do not treat it as a complete lighting design result.

Frequently Asked Questions

What are the common units of luminance?

Common luminance units include candela per square meter (cd/m², also called nit), foot-lambert (fL), lambert (L), stilb (sb), and apostilb (asb). The cd/m² is the SI standard. One foot-lambert equals approximately 3.426 cd/m², and one stilb equals 10,000 cd/m². Different industries and regions prefer different units.

How do you convert between nits and foot-lamberts?

To convert nits (cd/m²) to foot-lamberts, divide by 3.426. To convert foot-lamberts to nits, multiply by 3.426. For example, a 500-nit display is approximately 146 foot-lamberts. The foot-lambert is commonly used in the American cinema and projection industry, while nits are the international standard.

What is a stilb and how does it relate to nits?

A stilb (sb) is a CGS unit of luminance equal to one candela per square centimeter, which equals 10,000 cd/m² (nits). The stilb is rarely used in modern practice because it is inconveniently large for most applications. Most lighting and display specifications now use cd/m² or nits as the standard unit.

Why are there so many different luminance units?

Multiple luminance units exist because different measurement systems (SI, CGS, imperial) developed independently, and different industries adopted their preferred units. The cinema industry uses foot-lamberts, the scientific community prefers cd/m², and older European references may use lamberts or apostilbs. Standardization on cd/m² (nits) is increasingly common.

What are typical luminance values for common light sources?

Typical luminance values range widely: the sun's surface is about 1.6 × 10⁹ cd/m², a clear sky is about 8,000 cd/m², a fluorescent lamp surface is about 5,000-10,000 cd/m², a candle flame is about 5,000-15,000 cd/m², and a typical computer monitor is 250-500 cd/m². The human eye can perceive luminance over a range of about 14 orders of magnitude.