If we install lights at a certain height then how much light will be on the surface will be calculated by following equation.

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Measures both lux and foot-candles at a rapid sampling rate of 0.4 seconds. Display update rate is adjustable to 1 or 2 seconds.

Digital UVX Radiometer connects to one of the three interchangeable sensors (sold separately) to measure 254nm, 365nm or 302nm UV wavelengths

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A LED light bulb with a narrower beam angle may also seem brighter but the overall total luminous flux (Lumen) will be the same as the same LED light bulb with a lens which produces a wider beam angle. The brighter light is created by focusing the light within a more localized area, much like a magnifying glass can be used to focus the light of the sun. This is sometimes referred to the angular intensity of the light.

Digital UVX Radiometer connects to one of the three interchangeable sensors (sold separately) to measure 254nm, 365nm or 302nm UV wavelengths

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As light travels away from the point source it spreads both horizontally and vertically and therefore intensity decreases. In practice this means that if an object is moved from a given point, to a point double the distance from the light source it will receive only a ¼ of the light (2 times the distance squared = 4).

The 10 degree beam will be brightest in the center; however, the lux drops very fast away from the center. Thus, it totally is wrong to conclude that 10 degree beam is brighter than the 60 degree beam and hence10 degree beam is a better light.

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Photovoltaic J-Series UV meters for taking accurate and repeatable readings of UV light sources in either the 365nm or 254nm UV range

This is phenomena is called the inverse square law of illumination where the illuminance falls to a quarter of its value if the distance is doubled.

If the Lumens and distance between working plan and lamp is the same for all the four lights having beam angle of 10°,28°,38° and 60°.

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But all artificial light are affected from various factor and when the distance increases from the light source then the illuminance reduces according to distance.

Digital UVX Radiometer connects to one of the three interchangeable sensors (sold separately) to measure 254nm, 365nm or 302nm UV wavelengths

The inverse square law describes how the intensity of a light is inversely proportional to the square of the distance from the light source (the illuminator).

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Large LCD shows separate readings for lux and foot-candles in 1.375 in. H digits, plus selected source (daylight, tungsten, fluorescent or mercury).

Digital UVX Radiometer connects to one of the three interchangeable sensors (sold separately) to measure 254nm, 365nm or 302nm UV wavelengths.

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The amount of Lux at working plan is different. At narrow beam angle 10° it is more Lux at the center of Light (1390 Lux) and it will be reduce as we move from the center. While for wide angle 60° it is less Lux at the Center (39 Lux).

Taking this theory further, if an object at 10m from a light source receives 100 LUX, moving the object to 40m, it will receive only 1/16th of the light (4 times the distance, squared = 16) resulting in the object receiving only 6.25 LUX.

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As the luminous flux (Lumen) travels away from the light source the area over which it spreads increases, therefore the illuminance (lux) must decrease. The relationship is called as the inverse square law.

The LT45 LED light meter is useful for measuring and optimizing environmental light levels in a wide range of environments, including office buildings, manufacturing plants and warehouses, university campuses, schools, hospitals, and many other locations. OSHA regulates workplace lighting because illumination must be adequate for assigned tasks, and light meters are used to verify regulatory compliance, as well as state and local public safety codes and ordinances. Use of LED lighting is on the rise because it is more efficient to operate, it emits stable, high quality illumination, and the technology is dropping in price. The LT45 comes with a 9-volt battery, protective sensor cover, hard case, and user manual.

If we use a narrower beam angle, we will increase light intensity but reduce the size of the area being illuminated for the same height.

This compact, rugged light meter features Peak mode to capture your highest readings and relative mode indicating change in light levels for added flexibility. The min/max feature stores maximum and minimum readings on the large LCD with analog bargraph. Unit measures in lux or footcandles, and provides cosine- and color-corrected measurements.

The 60 degree beam has low center lux because it has more light spread over a larger area. The 10 degree beam is good to provide spot lighting. The 60 degree beam may be good for different lighting ambiance.

Digital UVX Radiometer connects to one of the three interchangeable sensors (sold separately) to measure 254nm, 365nm or 302nm UV wavelengths