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Light Converters

About Light Converters

Light and optics measurements span a wide range of physical quantities — how bright a source appears, how much light falls on a surface, how fine a printed image is, and how a light wave's color relates to its frequency. UnitConvertersLab's Light Converters bring together five specialized calculators covering the photometric, radiometric, and optical units that photographers, lighting designers, physicists, and engineers work with every day: luminance, luminous intensity, illumination, digital image resolution, and frequency-wavelength.

Luminance measures how bright a surface appears to the human eye, in units like candela per square meter (also called nits) and the older foot-lambert and stilb — the quantity behind display brightness specifications, road sign visibility standards, and photographic exposure calculations. Luminous Intensity measures how much light a source emits in a given direction, in candela and historical units like the hefner candle and carcel unit, still occasionally seen in older lighting references. Illumination (illuminance) measures how much light actually lands on a surface, in lux and foot-candle — the units printed on light meters used by photographers, cinematographers, and workplace safety inspectors to verify adequate lighting levels.

Digital Image Resolution converts between dots/pixels per inch, millimeter, and meter — essential for print designers and photographers translating between screen resolution (typically in pixels/inch) and print resolution (often specified in dots/mm or dots/meter in professional printing workflows). Frequency-Wavelength relates a light wave's frequency (in hertz and its metric multiples) to its position in the electromagnetic spectrum, a calculation used constantly in optics, spectroscopy, and telecommunications engineering.

Every converter on this page works the same way: pick a "from" unit and a "to" unit from the dropdown lists, type in a value, and get an instantly calculated, high-precision result — up to 12 significant digits — with no account required and nothing to install. Each tool is optimized for desktop and mobile alike, so you can pull up a quick conversion in the studio, the lab, or on set.

These five categories were chosen because light and optics specifications routinely mix SI photometric units, historical candle-based units, and printing-industry resolution units within the same project — a European lighting fixture spec in lux, a US photography light meter in foot-candles, and a print shop's resolution requirement in dots per inch all describe related but differently-scaled quantities. Rather than tracking down conversion factors from scattered references, you can get an exact, trustworthy answer here in seconds.

Our converters are perfect for:

  • Students and educators needing quick, dependable answers for coursework and exams
  • Photographers, cinematographers, and lighting designers converting between metering and specification units
  • Print and graphic designers translating between screen and print resolution standards
  • Physics and telecommunications professionals relating frequency to wavelength

Whether you're checking a light meter reading against a lighting design spec, converting a display's brightness rating, or translating an image's resolution for print, UnitConvertersLab's Light Converters are designed to be fast, accurate, and trustworthy. All conversion factors are drawn from standard, internationally recognized unit definitions, so you can rely on the same numbers used in textbooks, datasheets, and professional practice — anytime, on any device.

Frequently Asked Questions — Light Converters

Question: What light and illumination units can I convert?

Answer: Light Converters cover luminance (cd/m², nit, footlambert), illuminance (lux, foot-candle), luminous intensity (candela), luminous flux (lumen), luminous energy, frequency-wavelength, and digital image resolution — all the photometric and radiometric units used in physics, photography, and engineering.

Question: What is the difference between lux and lumens?

Answer: Lumens (lm) measure total luminous flux — the total amount of light emitted by a source. Lux (lx) measures illuminance — how much of that light falls on a surface. 1 lux = 1 lumen per square meter. A brighter source produces more lumens; a more focused beam produces more lux on the target.

Question: How do I convert candela to lumens?

Answer: Lumens = Candela × solid angle in steradians (lm = cd · sr). For a point source radiating equally in all directions (full sphere = 4π sr), total lumens = candela × 4π ≈ candela × 12.566. For a narrow beam, use the actual solid angle subtended.

Question: What is luminance?

Answer: Luminance is the luminous intensity emitted or reflected per unit area of a surface in a given direction, measured in candela per square meter (cd/m²), also called nits. It describes how bright a surface appears to the human eye — used in screen brightness, lighting design, and photography.

Question: What is the unit of illuminance?

Answer: The SI unit of illuminance is lux (lx), equal to 1 lumen per square meter. The imperial unit is the foot-candle (fc), equal to 1 lumen per square foot. 1 foot-candle = 10.7639 lux. Illuminance describes how well-lit a surface is.