1 watt (W):       = 0.27 lm @ 400 nm       = 25.9 lm @ 450 nm       = 220.0 lm @ 500 nm       = 679.0 lm @ 550 nm       = 683.0 lm @ 555 nm       = 430.0 lm @ 600 nm       = 73.0 lm @ 650 nm       = 2.78 lm @ 700 nm

A narrow band filter allows only a limited number of wavelengths to pass through it. Narrow band filters are usually specified at a specific central wavelength, a band pass indicating the range of wavelengths that will pass through it and a % transmission at the limits of the band pass. A 500nm narrow band pass filter with a band pass of 10 nm with a 5% cut off will pass the wavelengths between 495nm and 505nm. The transmittance above and below these wavelengths will be less than 5%.

The radiant power, at a specified wavelength and band pass that will produce a an output signal from a detector that is equivalent to the inherent noise in that detector.

The Tekneka EVM50 is an environment meter that measures temperature, humidity, air velocity, light, and sound. It features a 2″ LCD screen that dis...

A condition wherein the radiant flux density exceeds either or the capacity of a photodetector to emit electrons in a linear relationship to the incident flux and/or the current produced by the detector exceeds the capacity of the electronics to measure the current in a linear fashion.

When electrons vibrate they produce oscillating perpendicular electric and magnetic fields. The distance between sequential field intensity maxima is defined as the wavelength. These distances for visible radiation are very small and are usually expressed in unit lengths of nanometers (nm).

The LT40 LED light meter is useful for measuring and optimizing environmental light levels in a wide range of environments, including office buildi...

A thin metal wire purposely positioned inside a lamp bulb, that generates radiation in the visible, infrared and ultraviolet ranges when electrical current is passed through it. Tungsten material is often used, as it has great tensile strength, is very durable, and can be heated very near its melting point without evaporating rapidly. Lamp filaments are offered in a variety of designs optimized for specific applications.

The PCE-LMD 10 Light Meter/Data Logger has a large measuring range of 0 ~ 400kLux. The illuminance is measured using an external silicon photodiode...

UVB is the portion of the UV spectrum that covers the wavelength range between 280nm and 320nm. UVB radiation is typically used in UV curing and photolithographic applications as well as in certain medical applications. Exposure to UVB radiation (from lamps or electric arcs) can cause severe sunburn and cause eye damage.

Old definition of luminous intensity. One candlepower (cp) was the luminous intensity of a standard candle made of whale wax, weighing 1/6 lb, 7/8 in. in diameter, and burning 120 grains per hour. The current SI unit for luminous intensity is the candela (cd). One candela (cd) is the same as one candlepower thus a source with a luminous intensity of 10 candelas could be referred to as a 10 candlepower source.

Lightmeasurement unit

The current SI unit of luminous intensity. One candela is equivalent to 1 lumen/steradian. Used to express both Beam Intensity (Beam Candela) and Mean Spherical Intensity (Mean Spherical Candela). Also referred to as Candlepower (cp).

A chemical substance which is rendered insoluble upon exposure to light. By exposing photoresist through a mask, electrical circuits can be created by washing the unexposed areas and etching the material below. Photoresists are usually optimized for specific regions of the UV spectrum specified as UVC, UVB, and UVA depending on the type of lamp employed for the exposure.

Lux meters or light meters, (some with outputs), measure illumination in terms of luxes (lx) or foot candles (fc). A lux is equal to the total intensity of light that falls on a one square meter surface that is one foot away from the point source of light. A foot-candle is equal to the total intensity of light that falls on a one square foot surface that is one foot away from the point source of light. Since light usually contains different colors at different wavelengths, the reading represents the combined effects of all the wavelengths. Typically, standard colors or color temperatures are expressed in degrees Kelvin (K). The standard color temperature for the calibration of most lux meters is 2856° K, an amount that is more yellow than pure white. Lux meters or light meters are used to measure levels of light in schools, hospitals, production areas, laboratories, and passageways. They are also used to monitor light-sensitive displays in museums, art galleries, and archives. In the United States, lux meters are used to ensure that workplace, clean room, and industrial lighting complies with requirements from the Occupational Safety and Health Administration (OSHA). Other uses for lux meters or light meters include video, photographic, and architectural applications.

A hole through which radiant energy can pass. Angular aperture is the angle through which the most divergent rays can pass through a hole or lens. The aperture of a lens is often expressed in terms of an f/#. The f/# is the ratio of the focal length of the lens to its diameter. A lens with a focal length of 100mm and a diameter of 25mm would have an aperture of f/4.

A filter that does not pass light of wavelengths shorter that the cutoff wavelength and passes a wide band of wavelengths above the cutoff wavelength. The cutoff wavelength is specified at some point along the transition from maximum transmission to 0 transmission. The same filter can have different cutoff wavelengths depending upon the specified % transmission. The same filter may be specified as a 500nm cutoff filter with the 50% transmission point as the reference or a 485nm cutoff filter if the specification is the 5% transmission point, where the transmission at 485nm is 5%.

The ratio of the reflected flux to the incident flux from a surface. In some cases the measurement may be made with either the specular or diffuse component of the total reflected flux. Reflectance is expressed as a percent.

The CIE (Committee Internationale de l’Eclairage) is the international standards organization for illumination and color vision.

The SDL470 is a UVA/UVC Light Meter and Data logger. The SDL470 can measure both long wave and short wave UV irradiance under UVA and UVC light sou...

The intense peak of focussed power directly under a lamp. The maximum point of the irradiance profile. Measured in irradiance units (W/cm²).

PCE-LED 20 is a lux meter with an external LED light sensor. The cable of the sensor has an extended length of approx. 1.5 m / 4.9 ft. Different wo...

The invisible portion of the electromagnetic spectrum that extends from 0.75 microns to 1000 microns. Radiation in the near infrared (NIR) produces the sensation of heat.

The normal is the axis drawn perpendicular to an illuminated surface. The normal is the reference from which reflective, diffractive and refractive angles are measured. A ray with a zero degree angle of incidence arrives perpendicular to a surface. A ray with a 90° angle of incidence is parallel to a surface and may not strike it.

A cosine collector is a translucent light collector that compensates for normal blocking of radiation from flat surfaces. The cosine collector samples the radiation according to the cosine law through the hemisphere above the surface. A cosine collector may also be referred to as a Lambertian surface.

1 lm/m2/sr       = 1 candela/m² (cd/m²)       = 1 nit       = 1 x 10-4 lm/cm²/sr       = 1 x 10-4 cd/cm²       = 1 x 10-4 stilb (sb)       = 9.290 x 10-2 cd/ft²       = 9.290 x 10-2 lm/ft²/sr       = 3.142 apostilbs (asb)       = 3.142 x 10-4 lamberts (L)       = 2.919 x

A filter that reduces the intensity of the light passing through it without altering the relative spectral distribution of the energy. Neutral densities are given by the log base 10 of their attenuation. An attenuation of 100 gives a Neutral Desnity (ND) of 2. See Optical Density.

A device for measuring luminous intensity or luminance. A photometer employs a photopic filter which has a band pass that is matched to the human eye response. The S.I. units employed are lumens and lux.

The dynamic range is ratio of the maximum measurable signal before saturation to the minimum measurable signal above the noise. Typically the dynamic range is expressed in either decades (powers of 10) or bits (power of 2). A 5 decade dynamic range indicates that there is a factor of 100,000 between the maximum and minimum signals measurable with the apparatus. A dynamic range of 16 bits (264) indicates a factor of 65,532 between the minimum and maximum measurable signals.

The Extech UV510 UV light meter measures UVA light radiation from natural and artificial light sources. It offers a backlit dual display, cosine co...

The precision with which there is a direct relationship between the incident radiation and the resultant measurement value up to a point of saturation. A linearity of 1% states that the ratio of the measured value to that of the incident radiation will not vary more than 1% from the absolute.

The testo 540 lux meter can be used to measure artificial and natural light in the workplace. The testo 540 lux meter: compact, easy to use, precis...

A photodiode is a two electrode semiconductor device with an optical radiation sensitive junction in which the reverse current varies with the illumination. The wavelength sensitivity is a function of the materials used in the device. Silicon photodiodes are sensitive through most of the visible spectrum. InGaAs photodiodes are sensitive in the NIR region of the spectrum. GaP photodiodes are used for the UV region of the spectrum.

The lumen is the photometric unit of power. It is the flux emitted in a unit solid angle by a point source that has one candela luminous intensity.

The measure of a detector’s relative sensitivity as a function of incident wavelength. A typical spectral response curve will display the responsivity as a percentage at a given wavelength to wavelength of maximum responsivity.

The VUV is the portion of the UV spectrum below 190 nm. Electromagnetic radiation below 190nm is absorbed by oxygen in air. Physical or chemical interactions requiring VUV radiation must be performed in a nitrogen purged environment down to 160nm or in a vacuum chamber below 160nm.

A unit of energy equivalent to the amount of energy absorbed by one molecule of a material undergoing a photochemical reaction as determined by the Stark-Einstein law.

The ratio of the incident flux to the reflected flux from a scattering surface as opposed to a highly directional or specular (mirror-like) surface.

Dynamic range is also expressed in db (decibels), defined as 10 log10 (maximum signal / minimum signal). Five decades of dynamic range is equal to 50 db.

A device made up of dissimilar metals in which a small current is produced as a function of the difference in temperature of the materials at the junction. Thermocouples can be used for measurement of radiation in the infrared region of the spectrum.

The radiant flux density in W/cm2 required to produce a signal equal to the inherent noise of the detection system. The input irradiance at which the signal to noise ratio is 1.

The portion of the UV spectrum covering the wavelength range between 320nm and 400nm. This spectral region is used for many medical, UV curing and photolithographic applications. The earth’s atmosphere (at sea level) absorbs all wavelengths shorter than UVA. Prolonged exposure to UVA radiation will cause sunburn.

A device which reduces the amount of energy reaching a sensor. Attenuators are typically used when the radiant energy would saturate a detector. The QNDS,QNDS2 and QNDS3 filters are attenuators that reduce flux density at the detector by factors of 10, 100 and 1000, respectively.

Lightintensity

The unit of solid angle subtended by an area on the surface of a sphere equal the square of the radius of the sphere. One steradian can be visualized as a conic section with a solid angle of approximately 66°.

A filament description consists of a prefix letter, to indicate whether the wire is straight or coiled, followed by a number to indicate the arrangement of the filament on the supports. Prefix letters are usually one of three options

Lightmeasurement unit K

A surface whose emission or scattering follows Lambert's Cosine Law, in which the radiant intensity leaving a surface is proportional to the cosine of the angle from surface normal. See Cosine Collector.

Radiation emitted by vibrating charged particles. A combined oscillation of electric and magnetic fields that propagates through space at the speed of light. The electromagnetic spectrum is theoretically infinite, includes gamma, x-ray, UV, visible, IR, microwaves, and radio waves.

Having sensitivity characteristic similar to the human eye response. A photopic filter will have a band pass between 400 and 700nm with its highest transmission at 550nm with a spectral responsivity specified by CIE.

Ambient light is the light diffused in the environment surrounding a detector measuring the optical radiation from another source. This light contributes to the signal measured from the source. To make valid measurements, the contribution from the ambient light or background must be subtracted from each measurement.

One MSCP is equivalent to all the light emitted from all directions of one standard spermaceti candle. Mean spherical candlepower is the generally accepted method of rating the total light output of miniature lamps. 1 MSCP equals 12.57 (4 pi) lumens.

A device which measures the interaction between light and materials as a function of wavelength. A spectrometer is usually a monochromator with an integrated detector. A spectrograph does not have an exit slit, allowing a broad band of wavelengths to be measured simultaneously by means of a multi element detector or photographic plate.

Luminous intensity of a light source. The MSCP rating of a lamp is measured at the design voltage and is the total amount of light given off from a light source in ALL directions (measured in an integrating sphere).

A common, but loosely used, term for energy density, or radiant flux density, at a surface. (It is a precisely defined term in EB curing: 1 Gray (Gy) = 1 J/kg , a measure of absorbed energy per unit mass). In other technologies, the term usually applies to energy absorbed within the medium of interest, but in UV curing, is equated only to irradiant energy density arriving at the surface of the medium of interest. [The preferred shortened term is energy density, expressed in J/cm² or mJ/cm²]. May also be referred to as "dose" or "dosage".

The flux per unit solid angle leaving or entering a surface is proportional to the cosine of the angle with respect to the normal to the surface. In a cosine collector the rays that strike the surface at an angle of 60° from the vertical will have a contribution of 0.5 (cosine of 60°) that of identical rays arriving vertically.

Lightmeasurement device

Color temperature refers to the temperature, in degrees Kelvin, that a black body would have to be heated to in order to have a color similar to the reference. A 40W incandescent bulb has a color temperature of about 2680K while daylight at noon has a color temperature of about 5500K.

The LT45 LED light meter is useful for measuring and optimizing environmental light levels in a wide range of environments, including office buildi...

Kit for measuring the illuminance in workplaces, for example in offices or in production areas. Keep the Testo 440 air velocity and IAQ measuring i...

A CCD (charge coupled device) is a light detector with high sensitivity primarily in the visible spectrum. CCDs are typically made in either linear or two-dimensional arrays consisting of up to millions of individual detector elements. The 2D versions are used for image recording and are found in most digital camera used in both scientific and consumer applications.

The process of normalizing the signal output from a detector to that of a detector defined as a standard (usually defined by National Institute of Standards and Technology (NIST) under identical illumination conditions). Calibration can also be accomplished by the use of a standard source (lamp) whose output energy at specific wavelengths and measurement distances are traceable to the standard lamp defined by the governing standards body (NIST).

The ratio of the radiant power transmitted through a material to the incident radiant power. Transmittance is usually expressed as a percent. A filter with a 50% transmittance (at a specific wavelength) will absorb half of the light incident on it and allow half of it to pass through it.

Lightmeasurement unit lux

PCE-170 A Lux Meter with Built-In Sensor / Illuminometer for fast and accurate measurement of light / Measurement range from 0.00 to 40,000 lux / S...

Convenient 10-in-1 Environmental Meter measuring Air Velocity, Air Flow, Air Temperature, Type K Temperature, Heat Index, Humidity, Wet Bulb, Dew P...

Lightmeasurement for plants

A band eliminator filter allows the wavelengths above and below the filter cutoff to pass while suppressing the wavelengths within the band. These filters are also called notch filters. A 500nm band eliminator filter with a band pass of 10 nm would suppress the wavelengths between 495nm and 505nm.

Reflection from a mirror-like surface where in the coherence of the incident beam is maintained in the reflected beam. This is opposed to diffuse reflection wherein the reflected light is spread in all directions in a Lambertian-like manner.

Radiant power emitted into a full sphere (4p steradian) by a unit area of a source , expressed in W/m². An Integrating sphere is typically used to make this measurement.

A measure of the transmittance T through an optical medium.  OD = -log10T.   An OD of 1 is equivalent to 10% transmission. A 2 OD filter would have a transmission of 1%.

The lamp "T" number is the diameter of the lamp in increments of 1/8 inch. A "T-1" lamp is 1/8 inch in diameter, a "T-2" lamp is 1/4 inch in diameter, etc.

Footcandles is a unit of measurement of illuminance (how much light is striking a point on a surface). Once footcandle is equivalent to 10.764 lux.

Extech’s pocket-sized autoranging Light Meter offers wide light intensity ranges measuring up to 40,000Fc (400,000Lux) with high resolution to 0.01...

A black body is an object that absorbs all radiant energy that hits it. When heated a black body emits a well defined characteristic spectrum which can be used in characterizing the spectral responsivity of detectors. As there is no such thing as a perfect black body, black body simulators are used for this purpose.

The visible portion of the spectrum extends between 400nm and 700nm (per the CIE). It covers the wavelengths of light that the human eye can perceive.

What is the SI unit oflight

Radiant energy arriving at a surface per unit area, usually expressed in joules or millijoules per square centimeter (J/cm² or mJ/cm²). It is the time-integral of irradiance. (Other terms applied include "radiant exposure," "light dose," and "total effective dosage").

The response or sensitivity of any system as a function of incident wavelength. In radiometry, it is the output of a device versus wavelength.

A hollow sphere coated with a white diffusing coating in the interior. It is used for measuring the diffuse reflectance and transmittance of objects or the total flux from a source that is completely inside.

A diffraction grating is an optical component that separates light into its constituent wavelengths. Functionally equivalent to a prism, it disperses the light into its spectrum by employing grooves to diffract the light. The angle of the diffraction is a function of the wavelength.

The luminous intensity of a source expressed in candelas. Measured in an integrating sphere, Mean Spherical Candela is the total output of the source in lumens divided by 4pi steradians in a sphere.

Illuminance is a decisive factor for productivity, well-being, and health, especially in workplaces. Light sources that are too bright dazzle, whil...

A photomultiplier tube is a vacuum device in which a photocathode emits electrons when exposed to light. The electrons are then accelerated through electrostatic fields to metal plates where a greater number of secondary electrons are emitted. This is repeated through several stages. This amplifies the current by many thousands.

Bandwidth describes the size of a spectral segment. A bandwidth of 10nm indicates a range of 10nm of radiation. This can be, for example, between 500nm and 510nm, 1000nm and 1010nm or an equal size segment anywhere in the spectrum.

A unit of length equal to 10-9 m.  Abbreviated nm. Commonly used unit to define wavelength of light, particularly in the UV and visible ranges of the electromagnetic spectrum.

Many chemical products both medicinal and protective coatings can degrade when exposed to light. Photostability measurements are made to determine the principal wavelengths responsible for the degradation and the amount of exposure (dose) required to create a change that will be deleterious to the product’s efficacy. In photostability studies the effects from the visible wavelengths of light must be distinguished from the UV. Typically two detectors are employed with filtration limiting each to the measurement to only one spectral region.

This 4-in-1 meter measures Humidity, Temperature, Air Velocity and Light. The dual LCD simultaneously displays Temperature and Air Velocity or Rela...

The dark signal is the signal that flows in a photodetector when there is no optical radiation impinging upon it. This signal is created within the detector and the amplification circuits due to thermionic (temperature) effects.

Hioki FT3424 Lux Meter is designed for an extensive range of applications involving illumination equipment, lighting work, and facility management....

All biological organisms contain DNA. DNA is essential to reproduction. Optical radiation in the UVC range is capable of breaking the molecular bonds within DNA effectively killing microorganisms. Germicidal UV lamps are used for water treatment, sterilization of foods and their containers, and air purification, especially in hospital environments.

The energy per second (power) in a light beam expressed in Watts or Joules/second. (Radiant power). In photometric measurements the luminous power is typical expressed in lumens (lm) .

The PCE-LMD 5 Light Meter has a large measuring range of 0 ~ 400kLux. The illuminance is measured using an external silicon photodiode with a spect...

The dissipation of light (radiation) within a surface or medium, caused by the conversion of radiant (luminous) energy to a different form of energy, usually heat, by interaction with matter. The absorption is the "missing piece", when comparing the total reflected and transmitted energy with the incident energy. The ratio of the total absorbed radiant or luminous flux to the incident flux is called absorptance. The standard unit of absorptance is percent (%) or a factor between 0 an 1. Absorptance can also be inferred from the transmission through a medium. If the %transmission of a certain wavelength is 70% then the material has a 30% Absorptance.

Radiant flux incident per unit area of a surface; the power incident per unit area. The radiometric unit of measure is W/m² or factors thereof (mW/cm²). The photometric units of measure are lumens/m², lux, phot, and footcandles.

The science of radiation measurement. The detection and measurement of radiant energy either at specific wavelengths or band passes or as a function of wavelength over a broad spectrum. The measurement of the interaction of light with matter as to absorption, transmission, and reflectance.

UVC is the portion of the UV spectrum that extends from 190nm to 280nm. UVC is usually employed in water treatment and sterilization applications. UVC is also used in UV curing and photolithography in microelectronics applications. Exposure to UVC radiation (from lamps, arcs, or lasers) can cause severe biological damage.

The proportion of the standard tristimulus values used in color matching. Colors are compared by their CIE X, Y, and Z coordinates.

Also called the throughput of an optical system, it is the product of its entrance aperture and the solid angle in which light can be accepted at that aperture.

The SDL400 records data on an SD card in Excel format. Wide range to 10,000Fc or 100kLux. Cosine and color-corrected measurements. Utilizes precisi...

The angular width of a cone of light whose apex is at the source. Beamwidth is usually defined as the angle subtended by a cone encompassing 90% of the energy.

The characteristic of radiation that indicates its capability to produce chemical change. In our industry the term is usually used with reference to UV radiation and its effects on biological systems. Actinic strips are used in UV processing to monitor the intensity of sources. The color or optical density of the strip changes with the exposure. See the Optical Radiation Hazard applications page for a listing of ILT light measurement systems used to determine the actinic hazard of a light source.

The EA30 Light meter sports a compact and rugged design and features a large display. Multiple wide measuring ranges: 40,000Fc in 4 ranges and 400,...

Light measureapp

With the LED lux meter, important photometric factors in the field of light measurement can be determined. These include the tristimulus values of ...

The HD450 Light Meter measures from 0 to 40,000Fc and 0 to 400kLux with a 0.01Fc/0.1Lux resolution. Features: 5% accuracy, Peak mode (10µs), Relati...

Tekneka 430 is a mini light meter with a measuring range of 0 to 40kLux (0 to 4kFC). It has a 2-inch LCD screen with a bar graph that has 40 segmen...

The use of optical radiation in the cure of medical maladies. Photodynamic therapy is used in the treatment of skin conditions such as psoriasis, jaundice in newborns, and more recently in the treatment of certain types of cancer.

This compact and ruggedly designed meter has a wide measurement range to 99,990 Foot Candles in 5 ranges and 999,990 Lux in 5 ranges with 0.001Fc/0...

The relative spatial responsivity of a detector indicates the acceptance angle and percent of incident radiation at that angle that will strike the detector. The measurement is usually made in comparison to a perfect Lambertian surface.

A monochromator is a devise that uses a diffraction grating or prism to disperse light into a spectrum of its constituent wavelengths. The dispersive element is rotated such that only a narrow (monochromatic) band of light is permitted to exit the monochromator through a narrow aperture or slit.

The ratio of the output signal from a detector to the input signal. This may also be expressed as the minimum input irradiance level which will produce an output signal that exceeds the noise level of the detector; i.e. where the S/N is greater than 1.

Sampling a very narrow angle of the input beam, beam candela is only representative of the lumens per steradian at the peak intensity of the beam. The sampling angle need not be defined. Can be measured in Candela (cd) for steady sources or Effective Candela (eff cd) for flashing sources.

A densitometer measures the opacity or absorptance of a material. The measurement is usually expressed in AU (absorptance units) or OD (optical density).

The LT250W is a compact light meter with Bluetooth® connectivity, which allows building and maintenance professionals to view and share light inten...

Insufficient lighting can create security risks or result in OSHA crackdowns. The Extech LT300 light meter can determine whether you have adequate ...

The inverse square law correlates the relative intensity at varying distances from a point source. The relative intensity will diminish to a factor of the square root of the difference in distance. For example if at 2 meters from a source the intensity is 16 W/m², it will be 4W/m² at 4meters and W/m² at 8 meters. For extended (non-point) sources the intensity fall off approaches the inverse square law at a distance equivalent to 5 times the diameter of the source.