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

Product Information

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). No shadows should be allowed to fall on the light sensor during measurements, and the light sensor should be held perfectly horizontally and stationary for accurate results. How much lux do you need in a room? The next exposure meters, developed at about the same time but not displacing actinometers in popularity until the 1920s and 1930s, are known as extinction meters, evaluating the correct exposure settings by variable attenuation. [4] One type of extinction meter contained a numbered or lettered row of neutral density filters of increasing density. The photographer would position the meter in front of their subject and note the filter with the greatest density that still allowed incident light to pass through. In another example, sold as Heyde's Aktino-Photometer starting from the early 1900s, the photographer views the scene through an eyepiece and turns the meter to vary the effective density until the scene can no longer be seen. [6] The letter or number corresponding to the filter strength causing the "extinction" of the scene was used as an index into a chart of appropriate aperture and shutter speed combinations for a given film speed. [3] :72 Jones and Condit 1941). Although wide-angle average metering has largely given way to other metering sensitivity patterns (e.g., spot, center-weighted, and multi-segment), the values for K {\displaystyle K} determined for wide-angle averaging meters have remained. At best, a flat card is an approximation to a three-dimensional scene, and measurement of a test card may lead to underexposure unless adjustment is made. The instructions for a Kodak neutral test card recommend that the indicated exposure be increased by 1⁄ 2 step for a frontlighted scene in sunlight. The instructions also recommend that the test card be held vertically and faced in a direction midway between the Sun and the camera; similar directions are also given in the Kodak Professional Photoguide. The combination of exposure increase and the card orientation gives recommended exposures that are reasonably close to those given by an incident-light meter with a hemispherical receptor when metering with an off-axis light source.

It is commonly stated that reflected-light meters are calibrated to an 18% reflectance, [10] but the calibration has nothing to do with reflectance, as should be evident from the exposure formulas. However, some notion of reflectance is implied by a comparison of incident- and reflected-light meter calibration.

When to use a Lux Meter

It is not the app manufacturers' intention that a smartphone should replace a professional luxmeter. The fact that some apps work with so-called calibration functions sounds professional and smart but unfortunately it is often not possible to set the value accurately. Even if it is possible, the benefit is very small since the values outside the calibrated value are subject to extreme fluctuations. Even when using the same app in structurally identical smartphones different measuring results are achieved. Find sources: "Light meter"– news · newspapers · books · scholar · JSTOR ( September 2012) ( Learn how and when to remove this template message) The sensor will send a signal to the meter that is proportional to the amount of light that reaches the sensor after being collected by the optics and passing through the filter. The meter then converts the incoming signal (typically current or voltage) from the sensor into a reading of calibrated units such as Foot-Candles (fc) or Lux (lm/m Calibration of cameras with internal meters is covered by ISO 2721:1982; nonetheless, many manufacturers specify (though seldom state) exposure calibration in terms of K {\displaystyle K} , and many calibration instruments (e.g., Kyoritsu-Arrowin multi-function camera testers [11] ) use the specified K {\displaystyle K} to set the test parameters. to provide an exposure meter which is substantially uniformly responsive to light incident upon the photographic subject from practically all directions which would result in the reflection of light to the camera or other photographic register.

There are other types of specialized photographic light meters. Flash meters are used in flash photography to verify correct exposure. Color meters are used where high fidelity in color reproduction is required. Densitometers are used in photographic reproduction. a b Pears, Alan (June 1998). "Chapter 7: Appliance technologies and scope for emission reduction". Strategic Study of Household Energy and Greenhouse Issues (PDF). Department of Industry and Science, Commonwealth of Australia. p.61. Archived from the original (PDF) on 2011-03-02 . Retrieved 2008-06-26. {{ cite book}}: |work= ignored ( help) The corresponding unit in English and American traditional units is the foot-candle. One foot candle is about 10.764lx. Since one foot-candle is the illuminance cast on a surface by a one-candela source one foot away, a lux could be thought of as a "metre-candle", although this term is discouraged because it does not conform to SI standards for unit names.

Illumination requirement in a room depends upon its type and use. For example, in a bathroom, it is 100 lux whereas in a study room it is 300 lux. Because in a study room we need more illumination to read and write properly. You can measure the illumination level in a room at a particular place with the help of a lux meter and increase or decrease the number of light sources ( CFL or LED) accordingly. Later [ when?] meters removed the human element and relied on technologies incorporating selenium, CdS, and silicon photodetectors. Illuminance is measured with a flat receptor. It is straightforward to compare an incident-light measurement using a flat receptor with a reflected-light measurement of a uniformly illuminated flat surface of constant reflectance. Using values of 12.5 for K {\displaystyle K} and 250 for C {\displaystyle C} gives

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. 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. Lux Meter Working Principle The earliest calibration standards were developed for use with wide-angle averaging reflected-light meters

International Bureau of Weights and Measures (2019-05-20), The International System of Units (SI) (PDF) (9thed.), ISBN 978-92-822-2272-0, archived from the original on 2021-10-18 For incident-light meters, camera settings are related to ISO speed and subject illuminance by the incident-light exposure equation: Darlington, Paul (2017-12-05). "London Underground: Keeping the lights on". Rail Engineer. Archived from the original on 2018-11-16 . Retrieved 2017-12-20. Reflected-light meters measure the light reflected by the scene to be photographed. All in-camera meters are reflected-light meters. Reflected-light meters are calibrated to show the appropriate exposure for "average" scenes. An unusual scene with a preponderance of light colors or specular highlights would have a higher reflectance; a reflected-light meter taking a reading would incorrectly compensate for the difference in reflectance and lead to underexposure. Badly underexposed sunset photos are common exactly because of this effect: the brightness of the setting sun fools the camera's light meter and, unless the in-camera logic or the photographer take care to compensate, the picture will be grossly underexposed and dull. This pitfall (but not in the setting-sun case) is avoided by incident-light meters which measure the amount of light falling on the subject using a diffuser with a flat or (more commonly) hemispherical field of view placed on top of the light sensor. Because the incident-light reading is independent of the subject's reflectance, it is less likely to lead to incorrect exposures for subjects with unusual average reflectance. Taking an incident-light reading requires placing the meter at the subject's position and pointing it in the general direction of the camera, something not always achievable in practice, e.g., in landscape photography where the subject distance approaches infinity.