![]() Obscuring half the bulb (making it a hemisphere instead of a full sphere), a 1 cd bulb will emit only 6.28 lm. ![]() ![]() For a bulb emitting 1 cd, that bulb would also have a luminous intensity of 12.57 lm. To show the difference between lumens and candela, let’s go back to the example previously used for candela with the partially obscured light bulb. To put it simply, the lumen rating is how much total visible light is produced by a light source. The lumen (lm) is a measurement of luminous flux, or the total amount of visible light. A watt measures the amount of energy a luminaire uses, while the term lumen is a better way to describe brightness.Lumens are now the most common measurement for a light bulb. Watt: A unit of power that measures the amount of energy a luminaire uses. ![]() One lux is equal to one lumen per square meter. Lux: The metric equivalent to footcandle, this unit of measurement is used to describe the illuminance measured per area unit. Luminous Flux: A measure of the energy released from a source in the form of visible light. Luminance: The brightness of a surface or object when viewed from a particular angle, measured in candelas per unit area (square feet or square meters). Luminaire: A complete electric light unit also referred to as a light fixture. In simpler terms, it measures the amount of brightness coming from a light source the higher the number of lumens, the brighter the light. Lumen (lm): A unit of measure of the total light emitted per second from a luminous source. The lower the Kelvin value, the more yellow/amber the light appears. The higher the Kelvin value, the bluer the light appears. Kelvin (or degrees Kelvin): A unit of measurement describing the hue of the light emitted from a specific light source. Illumination: The use of lighting to achieve practical or aesthetic effects. Illuminance: The amount of light that falls on a surface, measured in footcandles (Fc). Glare: The presence of high luminance (bright lighting) caused by insufficiently shielded light sources in the field of view or reflected sources of excessively bright light. One footcandle is equal to one lumen per square foot. ![]() This concept is more useful in lighting design than considering watts alone since lighting output is better described in lumens.įlicker: Rapid, repeated changes in the brightness intensity produced by a luminaire.įootcandle (Fc): The imperial equivalent to lux, this measurement unit describes the illuminance measured per unit of area. The Kelvin scale illustratedĮfficacy (or Luminous Efficacy): A measure of how effectively a light fixture converts electric power into visible light. CCT is measured in terms of temperature using the Kelvin scale. An example of varying CRIs at the same color temperatureĬorrelated Color Temperature (CCT): A description of the color appearance of the light a luminaire produces-in terms of warm (yellow) or cool (blue). The higher the CRI, the better the color rendering ability of a light source. The candela was initially rooted in the concept of the illuminance of a standard wax candle.Ĭolor Rendering Index (CRI): A measurement of how accurate (or “true”) a light source makes the color of an object appear. So we’ve put together this glossary of basic lighting terms for you to access any time you need to differentiate a lux from a lumen or decipher the difference between a light source’s CRI and CCT.Īmpere (Amp): The basic unit of measurement for electrical current, representing the amount of electric charge in motion.Ĭandela (cd): In simple terms, a candela is a unit of measurement that describes the amount of light emitted in a particular direction. As any architect or designer can tell you, lighting has its own lingo and terminology. ![]()
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