Radiant exposure

ISO 9370, Plastics - Instrumental determination of radiant exposure in weathering tests - General guidance and basic test method, 1997. 

The general requirements for accelerated weathering apparatus are given in ISO 4892-1 [29], whilst ISO 4892 Parts 2-4 [26-28] deal more specifically with xenon arcs, fluorescent tubes and carbon arcs respectively. ISO 4892 refers to ISO 9370 [30] (Instrumental determination of radiant exposure in weathering tests), and CIE publication 85 (Solar spectral irradiance) [31]. 

Figure 12.3 Examples of the weathering performance of (a) a stabilised HDPE nonwoven and (b) a polyamide/polyester nonwoven deliberately unstabilised against ultraviolet radiation. Both were exposed to artificial weathering using three different types of apparatus and to natural weathering in two locations. All results are plotted against radiant exposure (total ultraviolet light energy...

Fluence is used in photochemistry to specify the energy delivered in a given time interval (for instance by a laser pulse). This quantity may also be called radiant exposure. 

Radiant exposure (H) The irradiance, E, integrated over the time of irradiation (f Edt, simplified expression H = E t when the irradiance is constant over the time considered). The SI unit is J mT. For a parallel and perpendicularly incident beam not scattered or reflected by the target or its surroundings fluence (Hq) is an equivalent term. 

S refers to the area of the radiating element for the term radiance, and to the area of the irradiated element for the term irradiance and (radiant) exposure e is the angle between the normal to the surface and the direction of the radiating beam, whic is assumed to be confined to a narrow solid angle. 

The output from the lamps can vary between the tubes and also along the length of the tubes. The UV and VIS levels should therefore be mapped across the test chamber to ensure that the samples are placed at points of equal irradiance, 10%. The specimens should be placed only in the exposure area where the irradiance is at least 90% of the maximum irradiance unless the exposure time is increased. It can also be useful to reposition the samples during the exposure period to ensure that each specimen receives an equal amount of radiant exposure. If a combination of UV and VIS is used (i.e.. Option 2, also allowed in Option 1), it is important to make sure that the sample is exposed to both radiation components independent of its location in the chamber. 

Level of Irradiance on Sample Area and Radiant Exposure in... 

Description and recommendation of methods and devices for determining irradiance and radiant exposure as well as for measuring temperature... 

Development of specific measuring devices for irradiance/radiant exposure and surface temperature... 

ISO 9370 (Table 5.1) contains valuable information and recommendations on important characteristics for the instruments used and provides a guide for selection and use as well as calibration procedures of these radiometers. The guide includes natural and simulated exposure testing. Instrumental techniques include the continuous measurement of irradiance in specific wavelength bands and the accumulation (or integration) of instantaneous data to provide a total radiant exposure (dosage). 

Figure 5.12 Measurement of irradiance and radiant exposure (bandpass) on sample area (principle).

LEVEL OF IRRADIANCE ON SAMPLE AREA AND RADIANT EXPOSURE IN PHOTOSTABILITY TESTING... 

The level of irradiance and the radiant exposure are two important parameters for conducting reliable photostability tests. The level of irradiance should be specified on sample level and the measurements (irradiance, radiant exposure) must be done on this sample level (where the drug, e.g., is exposed to the light source). 

Radiant exposure (H) The irradiance, E, integrated over the time of irradiation. SI unit is J nr2. 

Let us take another angle in this consideration and predict which values of acceleration factors can be anticipated, using direct comparisons of UV radiant exposures in the weathering box and the real world. 

TABLE 16.3 The annual UV radiant exposures (295-385 nm) in Homestead, FL (latitude 25°27 North, longitude 80°30 West, elevation 7 ft) and Buckeye, AZ (latitude 33°23 North, longitude 112°35 West, elevation 1055 ft), 45° south exposure... 

Table 16.3 shows examples of the annual UV radiant exposure (295-385 nm) in Florida and Arizona. 

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