Digital Light Meter, Hand-Held Luxmeter, Illuminance Meter Photometer 0~100,000Lx

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In practice, additional complications may arise. Many neutral test cards are far from perfectly diffuse reflectors, and specular reflections can cause increased reflected-light meter readings that, if followed, would result in underexposure. It is possible that the neutral test card instructions include a correction for specular reflections. Achieving an illuminance of 500lx might be possible in a home kitchen with a single fluorescent light fixture with an output of 12 000lumens. To light a factory floor with dozens of times the area of the kitchen would require dozens of such fixtures. Thus, lighting a larger area to the same illuminance (lux) requires a greater luminous flux (lumen).

The incident-light calibration constant depends on the type of light receptor. Two receptor types are common: flat ( cosine-responding) and hemispherical ( cardioid-responding). With a flat receptor, ISO 2720:1974 recommends a range for C {\displaystyle C} of 240 to 400 with illuminance in lux; a value of 250 is commonly used. A flat receptor typically is used for measurement of lighting ratios, for measurement of illuminance, and occasionally, for determining exposure for a flat subject. ISO 2720:1974 calls for reflected-light calibration to be measured by aiming the receptor at a transilluminated diffuse surface, and for incident-light calibration to be measured by aiming the receptor at a point source in a darkened room. For a perfectly diffusing test card and perfectly diffusing flat receptor, the comparison between a reflected-light measurement and an incident-light measurement is valid for any position of the light source. However, the response of a hemispherical receptor to an off-axis light source is approximately that of a cardioid rather than a cosine, so the 12% "reflectance" determined for an incident-light meter with a hemispherical receptor is valid only when the light source is on the receptor axis. With a slightly revised definition of reflectance, this result can be taken as indicating that the average scene reflectance is approximately 12%. A typical scene includes shaded areas as well as areas that receive direct illumination, and a wide-angle averaging reflected-light meter responds to these differences in illumination as well as differing reflectances of various scene elements. Average scene reflectance then would be The lux (symbol: lx) is the unit of illuminance, or luminous flux per unit area, in the International System of Units (SI). [1] [2] It is equal to one lumen per square metre. In photometry, this is used as a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface. It is analogous to the radiometric unit watt per square metre, but with the power at each wavelength weighted according to the luminosity function, a model of human visual brightness perception, standardized by the CIE and ISO. [3] In English, "lux" is used as both the singular and plural form. [4] Hi friends, in this article, I am going to discuss about the lux meter working principle and its application.The general observation is that the displayed values on the Sony devices and the Samsung and Nokia smartphones were well above the reference values, while as a rule the the iphones displayed values well below the reference values. The median deviation from the reference value measured by all the apps on the Android smartphones and on the Windows phones was on average 60% above the reference value. The median deviation of all values measured with all the different iphones was approx. 60% below the reference value. Westphal, Wilhelm Heinrich (1952). "Nox, Dunkelleuchtdichte, Skot". In Westphal, Wilhelm H. (ed.). Physikalisches Wörterbuch (in German) (1ed.). Berlin / Göttingen / Heidelberg, Germany: Springer-Verlag OHG. pp.125, 271, 389. doi: 10.1007/978-3-662-12706-3. ISBN 978-3-662-12707-0 . Retrieved 2023-03-16. pp.125, 271: Nox, abgek[ürzt] nx, Einheit der Dunkelbeleuchtungsstärke (Dunkelleuchtdichte), welche für zahlenmäßige Angaben und zum Anschluß der Dunkelbeleuchtungsstärke an die normale Beleuchtungsstärke 1940 von der Deutschen Lichttechnischen Gesellschaft [ de] geschaffen wurde. Bezüglich der Farbtemperatur der Strahlung und des Anschlusses von Zahlenwerten der Beleuchtungsstärke E und der Dunkelbeleuchtungsstärke E gelten analog die gleichen Festlegungen wie bei der Dunkelleuchtdichte und dem Skot (sk). Für eine Strahlung der Farbtemperatur T 1= 2360K gilt: 1nx= 10 −3lx (Lux). Für eine beliebige Strahlung bekannter spektraler Strahlungsleistung S 1 lautet die Verknüpfungsbeziehung zwischen in 10 −3lx gemessenem Zahlenwert { E} der Beleuchtungsstärke und in nx gemessenem Zahlenwert { E} der Dunkelbeleuchtungsstärke: { E} nx= (2,161± 0,001)· { E} 10 −3lx· ∫ S λ V λ,W dλ/ ∫ S λ V λ dλ, wobei V λ die relative spektrale Hellempfindlichkeit und V λ,W die relative spektrale Dämmerungsempfindlichkeit des menschlichen Auges nach Weaver [A] bedeuten. [...] Dunkelleuchtdichte. [...] Ist das Auge dunkeladaptiert, d.h. einer Leuchtdichte von weniger als 0,01 asb ausgesetzt, so gilt infolge des Purkinje-Phänomens eine von der spektralen Hellempfindlichkeitskurve abweichende, nach dem kurzwelligen Ende des Spektrums hin verschobene Empfindlichkeitskurve des Auges, die Stäbchenkurve des Dämmerungssehens. Unter Zugrundelegung dieser Empfindlichkeitskurve hat man 1940 in Deutschland die Dunkelleuchtdichte mit der Einheit Skot (sk) so festgesetzt, daß bei einem Licht der Farbtemperatur 2360° K 1sk= 10 −3asb gilt. 1948 ist von der Internationalen Beleuchtungskommission (IBK) die Bezugstemperatur auf 2046K, die Erstarrungstemperatur des Platins, festgesetzt worden. Die Bezeichnung Skot wurde von der IBK nicht übernommen, dafür soll " skotopisches Stilb" gesagt werden. Als höchstzulässiger Grenzwert für die Dunkelleuchtdichte ist in Deutschland 10Skot festgesetzt worden, um eine Verwendung der Dunkelleuchtdichte im Gebiet des gemischten Zapfen- und Stäbchensehens zu vermeiden, da in diesem Bereich die photometrischen Maßgrößen wegen der allmählich gleitenden Augenempfindlichkeitskurve ihren Sinn verlieren.

The earliest calibration standards were developed for use with wide-angle averaging reflected-light metersThe peak of the luminosity function is at 555 nm (green); the eye's image-forming visual system is more sensitive to light of this wavelength than any other. For monochromatic light of this wavelength, the amount of illuminance for a given amount of irradiance is maximum: 683.002lx per 1W/m 2; the irradiance needed to make 1lx at this wavelength is about 1.464 mW/m 2. Other wavelengths of visible light produce fewer lux per watt-per-meter-squared. The luminosity function falls to zero for wavelengths outside the visible spectrum. Selecting luxmeters or light meters requires certain performance specifications include photocell, illumination range, Lux resolution, operating temperature and foot candle resolution. Special features include low battery Indicators, low voltage, alarms, remote light sensors, built-in memory, auto power off, zero function etc.

Low-Light Performance Calculator". Archived from the original on 2013-06-15 . Retrieved 2010-09-27. difference algorithm, where lights are switched on at a lower light level than they switch off, thus taking ensuring the difference between the light level of the 'on' state and 'off' state is not too bigFor incident-light meters, camera settings are related to ISO speed and subject illuminance by the incident-light exposure equation: Lux meters are used to measure levels of light in schools, hospitals, production areas, laboratories. They are also used to monitor light-sensitive displays in museums, art galleries etc. Illumination (symbol E) The earliest exposure meters were called actinometers (not to be confused with the scientific instrument with the same name), first developed in the late 1800s after commercial photographic plates became available with consistent sensitivity. These photographic actinometers used light-sensitive paper; the photographer would measure the time required for the paper to darken to a control value, providing an input to a mechanical calculation of shutter speed and aperture for a given plate number. [3] :69 They were popular between approximately 1890 and 1920. [4] Extinction types [ edit ] Dremo extinction meter [5]