Radiant flux

Artificial surfaces must be resistant to cigarette bums, vandaUsm, and other harm. Fire resistance is most critically evaluated by the NBS flooring radiant panel test (10). In this test, a gas-fired panel maintains a heat flux, impinging on the sample to be tested, between 1.1 W/cm at one end and 0.1 W/cm at the other. The result of the bum is reported as the flux needed to sustain flame propagation in the sample. Higher values denote greater resistance to burning results depend on material and surface constmction. Polypropylene turf materials are characterized by critical radiant flux indexes which are considerably lower than those for nylon and acryflc polymers (qv) (11). 

Variously called, in the literature, emittance, total hemispherical intensity, or radiant flux density. 

The radiant flux can be determined as a function of frequency from Planck s distribution law for emission ... 

The sun radiates approximately as a blackbody, with an effective temperature of about 6000 K. The total solar flux is 3.9 x 10 W. Using Wien s law, it has been found that the frequency of maximum solar radiation intensity is 6.3 x 10 s (X = 0.48 /rm), which is in the visible part of the spectrum 99% of solar radiation occurs between the frequencies of 7.5 X 10 s (X = 4/um) and 2 x 10 s (X = 0.15/um) and about 50% in the visible region between 4.3 x 10 s (X = 0.7 /rm) and 7.5 X 10 s (X = 0.4 /Ltm). The intensity of this energy flux at the distance of the earth is about 1400 W m on an area normal to a beam of solar radiation. This value is called the solar constant. Due to the eccentricity of the earth s orbit as it revolves around the sun once a year, the earth is closer to the sun in January (perihelion) than in July (aphelion). This results in about a 7% difference in radiant flux at the outer limits of the atmosphere between these two times. 

Using Wien s displacement law, determine the mean effective temperature of the earth-atmosphere system if the resulting longwave radiation peaks at 11 /rm. Contrast the magnitude of the radiant flux at 11 pm with that at 50 pm. 

Irradiance The radiant flux striking a unit area of a surface. 

Reflectance A measure of the extent to which a surface is capable of reflecting radiation, defined as the ratio of the intensity of reflected radiant flux to the intensity of the incident flux. 

Radiant energy Radiant flux or power Radiant intensity... 

Radiant flux per unit solid angle in a given direction. 

Radiant flux per unit area incident on a surface. 

X-ray production by electron excitation, 5-9, 27, 28, 98-102, 176-179 X-ray radiance, definition, 6 X-ray radiant energy, definition, 6 X-ray radiant flux or power, definition, 6... 

Combustion may be induced by lower pressures by preheating the strand, by providing a sufficient incident radiant flux, by adding certain catalytic agents, and by adding small amounts of various fuels. 

Transmittance.Transmittance is the ratio of the radiant flux transmitted by a material to the incident flux. 

External radiant flux is not affected by the flame, e.g. thin flame. 

Flame incident radiant flux ( "r) and total radiant energy (XtQ) might be estimated from measurements. 

Figure 9.17 Burning rate of vertical PMMA slabs versus external radiant flux for various water application rates [19]...

If the fuel is modified such that k l-1/2, then the radiant flux for 1 small becomes consistent with conduction as q" l1/2, and the radiation heat loss goes as required, l5/2. Alternatively, if radiation is believed to dominate, it might be useful to consider k large and ignore II5 but require that... 

Surface Flammability of Building Materials Using a 8 Ft. Tunnel Furnace, 1984. Critical Radiant Flux of Floor Covering Systems Using a Radiant Heat Energy Source [NIST(NBS) Flooring Radiant Panel], 1993. 

Radiant intensity can be described as the amount of power (watt) heading in your direction, i.e., per steradian, from a light source. The total amount of power emitted by the source is the radiant flux (watt). If you integrate the radiant intensity over all solid angles, you get the total radiant flux. If it is weighted by the photopic response, then it is the luminous intensity and the luminous flux. 

---