Light meters

Blackness test A filter test for air or the products of combustion, in which a dust spot is formed on filter paper, the degree of reflection is determined by a light meter, and the result is related to a standard. 

Levels, tapes, thermometers, hydrometers, light meters, smoke detectors, audio-sensors. Features such as cradle rails, safety eyes and climbing irons should be incorporated into the design of the building. 

Fig. A.3. Light meter used by the author (Model 8020, Pelagic Electronics). For total light measurements, the signals are integrated with capacitors. Milliammeter reading is automatically reset at full-scale position, and the number of resets is digitally indicated below the meter. The box at the right contains a photomultiplier and sample compartment.

A designer of lighting systems was called in. He recommended surface mounted fluorescent fixtures, which he considered more efficient than the recessed ones. The laboratory operator scanned all work areas with a light meter after the job was completed. The light was even and well within recommended levels. Fiirther-more, there were never any problems with the fixtures themselves, except for an occasional change of tubes. 

Sulfur vapor consists of a mixture of species that includes S8, S6, S4, and S2 (which like 02 is paramagnetic). Because the S8 molecule is nonpolar, it is soluble in liquids such as CS2 and C6H6. Selenium also consists of cyclic molecules that contain eight atoms, and tellurium is essentially metallic in character. In their vapors, several species are found that contain 2, 6, or 8 atoms. Both are useful as semiconductors, and selenium has been used in rectifiers. Because the electrical conductivity of selenium increases as the intensity of illumination increases, it has been used to operate electrical switches that open or close as a light beam is broken. Selenium was also used in light meters, but other types of meters are now available that are more sensitive. Table 15.1 gives a summary of the properties of the group VIA elements. 

The photosensitive nature of selenium makes it useful in devices that respond to the intensity of light, such as photocells, light meters for cameras, xerography, and electric eyes. Selenium also has the ability to produce electricity directly from sunlight, making it ideal for use in solar cells. Selenium possesses semiconductor properties that make it useful in the electronics industry, where it is a component in some types of solid-state electronics and rectifiers. It is also used in the production of ruby-red glass and enamels and as an additive to improve the quality of steel and copper. Additionally, it is a catalyst (to speed up chemical reactions) in the manufacture of rubber. 

BCNO selenium in their cells, but the element is also very useful in machines such as photocopiers and light meters. Selenium metal conducts electricity much better when exposed to light, which... 

One of several units of illumination based on units per square metre. One lux = 0.0929 foot-candles, and 1 foot-candle = 10.764 lux. Relationships between lux and pE.m 2.s 1 is variable and depends on light source, light meter used, geometrical arrangement of the exposure environment and possible light reflections, so one lux = 0.015pE.m 2.s (range of 0.012 to 0.019). Synonymous term is lumen (i.e., 1 lux = 1 lumen). Volume 1(3,10). 

Wynn Bullock was a contemporary and good friend of Ansel Adams. While Wynn was renowned for his print quality, he rarely used a light meter and when he did it was in the most rudimentary fashion—aim at the subject and take a reading. Ansel was often seen coercing Wynn to learn the Zone System. Finally, Wynn acquiesced and purchased a spot meter and densitometer. Ansel told him what to do, and Wynn began testing his materials. 

Three common classes of instruments are used for measuring the amount of incident light (1) photometers or light meters, which measure the available illuminating power, a quantity related to the wavelength sensitivity of the human eye (2) quantum or photon meters, which measure the number of photons and (3) radiometers, which measure the total energy of the radiation (Fig. 4-4). 

By definition, photometers do not respond to radiation in the infrared or the ultraviolet (Fig. 4-4a). They are light meters in the sense that they mimic human vision that is, they respond to photons in the visible region, similar to the light meter on a camera. A candle is a unit of luminous intensity, originally based on a standard candle or lamp. The current international unit is called a candela (sometimes still referred to as a candle ), which was previously defined as the total light intensity of 1.67 mm2 of a blackbody radiator (one that radiates maximally) at the melting temperature of pure platinum (2042 K). In 1979 the candela was redefined as the luminous intensity of a monochromatic source with a frequency of 5.40 x 1014 cycles s-1 (A, of 555 nm) emitting 0.01840 Js-1 or 0.01840 W (1.464 mW steradian-1, where W is the abbreviation for watt and steradian... 

The terms "lumens" and "lux" were introduced into pharmaceutical photostability testing because they are units found on commercial light meters. No one ever questioned the appropriateness of the term to this field of study. It has no application in the field of pharmaceutical photostability testing. 

The extinction coefficient 17 may be calculated from measurements of I made by a light meter. The Secchi disk is another time-honored device for estimating light penetration in a lake. In 1865, P. A. Secchi developed this method, which was subsequently used aboard the papal yacht, S. S. L immacolata Concezione. The Secchi disk is about 20 cm in diameter, col-... 

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