Radiometry Radiometry is defined as the measurement of electromagnetic radiation within the frequency range between 3×1011 and 3×1016 Hz. Its wavelengths ranges between 0.01 and 1000 micrometers (mm), having regions commonly known as the ultraviolet, the visible and the infrared. Units that are commonly used are watts/m^2 and photons/sec-steradian. The four basic concepts are:
Radiant Flux Radiant flux is defined as the total radiant power emitted from a source or received by a surface. It is also known as the rate of flow of radiant energy through a certain area or out of a certain solid angle. The SI unit of radiant flux is Watt. Radiant Intensity Radiant intensity is defined as the directed angular density of radiation from a source. Radiant intensity in a given direction is the sum of the power contained in all the rays (cones) emitted in that direction by the entire source (i.e., power per solid angle). Its SI unit is Watt/Steradian (Watt/sr). Irradiance Irradiance is the measure of radiant flux incident on an object’s surface (radiant flux per unit area). Its SI unit is Watt/square meter (Watt/m2). Radiance Radiance is the measure of the total radiant intensity per unit projected area. Its SI unit is Watt/square meter Steradian (Watt/m2 sr). Photometry Photometry is defined as the measurement of light defined as the electromagnetic radiation detectable by the human eye. It is thus confined to the wavelength ranging from 360 to 830 nanometers (nm; 1000 nm = 1 µm). Photometry is just like radiometry excluding the fact that everything is weighted by the spectral response of the eye. In visual photometry, we use the eye as a comparison detector. However, physical photometry uses either optical radiation detectors designed to mimic the spectral response of the eye, or spectroradiometer having appropriate calculations to do the eye response weighting. Typical photometric units are lumens, lux, candelas, and a host of other bizarre ones. Luminous Flux Any source of light emits energy in the form of electromagnetic waves. We speak of light energy as ‘flux’ and luminous flux is defined as the measure of the flow of light energy emitted by a source or received by a surface. The quantity is derived from the radiant flux, W (in Watts), by evaluating the radiation in accordance with the relative luminous efficiency of the ‘standard eye’ (CIE Standard Luminosity Function, V*). The unit is lumen (lm). lm = 6 83 x W (Watt) x V* Luminous Intensity Luminous Intensity defines the power of a light source. It is the quantity of luminous flux emitted in a given direction per solid angle (in steradian). Its SI unit is candela (cd). 1 cd = 1 lumen per steradian. (For practical purposes, one candela power.) Illuminance It is defined as the measure of the concentration of luminous flux falling upon a surface. It is written in lumens per unit area. Its unit is lux (lx). 1 lx = 1 lumen per square meter (lm/m2) The original non-metric British unit is the foot-candle. 1 foot-candle = 1 lumen per square foot (lm/ft2) Luminance It is also known as photometric brightness and defined as the measure of the flux emitted from, or reflected by, a relatively flat and uniform surface. Luminance may be expressed as luminous intensity per unit area. Its unit is candelas per square meter (cd/m2), or nit. The original non-metric British unit is the footlambert (fL) 1 fL = 1 candela/*ft2. We at ITC INDIA Pvt. Ltd. provide Photometry Testing Services for all kinds of LED lights and luminaries. Our Photometry Testing mainly includes testing against LM-79 and LM-80. Apart from these standards, we also provide LED and luminaire testing services against many other standards like IEC 60598, IEC 60529, IEC 60068 etc. At ITC INDIA, Medical Device Testing, Electrical/Electronic Equipment testing, Environmental testing, NDT testing and many other Testing services are also available. For more information, contact [email protected] or fill the form below to get your Testing QUOTE today. Comments are closed.
|