Light measurement units

The standard unit of light measurement (the light flux) is the lumen, which is the amount of energy (power, watts) emitted or received (Joules per second). At 555 nm, 1 lumen = 0.00147 watts = 0.00147 J.s-1. This is sometimes called a lightwatt . 

Scattering Coefficient measure of the ability of particles to scatter light measured in number proportional to the "amount" of light scattered per unit distance. 

A laser-based detection system for NO2 gas (which is an industrial hazard and common environmental pollutant) was developed by Koybayashi et al.4. This was achieved by splitting light, from an Ar-ion multi-line laser, into two paths, one passing through a measurement gas, and the other being transmitted directly to the measurement unit as a reference signal. The detection unit contained two filters to separate the two chosen laser lines, and these were then detected on separate optical receivers. One of these chosen laser lines coincided with a strong absorption line in the NO2... 

The formal similarity between Equations (27) and (39) helps us understand somewhat better the physical significance of the Rayleigh ratio Re. It is directly proportional to the attenuation of the light per unit optical path, measured as absorbance, when the attenuation is due to scattering alone. In this case absorbance is more properly called turbidity. 

The units of light intensity are so numerous that we often become confused. But we have only one which we can measure, it is the luminosity, which is the same as the above luminous intensity of light. Other units are derived from the luminosity. The new unit of luminosity is the candela and 1 candle power equals 1.0l8 candelas. 1 candela means... 

The black plate is used to compensate for a variation in the quantity of inner stray light of the optical measurement unit (the inner stray light means the light which is detected at the measurement of a completely black plate without invading light into the optical measurement unit from the outside). 

In the visible region, the terminology is somewhat different it is called photometry and is based on the human response to visible light. The unit of source intensity is the candle and the radiance of the source becomes the brightness, while the irradiance is called the illuminance (measured in lux) or the illumination (measured in footcandles). The lumen is the unit of power (in watts) while lux is the power per unit area, expressed as lumen m-2 or watts m-2. Note that the units of photometry relate to standardized human perception. Thus, a monochromatic UV source may have high irradiance but zero illuminance because none of the energy can be perceived by the human eye. However, many sources of UVR are also powerful visible light sources and are rated by manufacturers in photometric terms. 

While light measurement or any deeper involvement with the optical aspects of pyrotechnics is not contemplated in this book, a short review of units of measurement is indicated. That the profusion and confusion of units must be bewildering has been plaintively noted in the book by Middleton. The books on optics by Sears and Hardy and Perrin, the discussion of the subject by Shidlovsky, and informative papers and tables from Temperature have been consulted. Units of special interest are ... 

Fig. 4.15 The optical measuring system of ISO-box 1 position of filters during calibration 2 illumination unit 3 window cleaning device 4 measuring area 5 light detection unit. Dimensions in mm Reprinted with permission of ISO. See footnote of Fig. 3.3...

At the level of 177 kg per cubic metre and more, rubber is in a very high concentration. For example, the level of 236 kg per cubic metre will have a volume of 0.18 cubic metre, and take about 25% of the total volume. Considering the air the rubber will bring in, rubber concrete at this level will be very light. In a few cases, the measured unit-weight values of rubber concrete at this level are as low as 1600 kg per cubic metre. Applications may include outdoor sports and recreational facilities like tennis courts, basketball courts, walkways, etc., with a design strength of 14 MPa or less. 

Illumination is the quantitative measurement of light. The watt is the measurement unit of light power. Light can also be measured in terms of the luminance of light as it encounters the eye. Units of luminance include lumens, candela, and apostilb. 

Sensitivity The signal current developed per unit of incident light, measured in micxoamps per lumen. 

---