Lambertian radiator

For InjO mode reflectometers, a non-Lambertian radiation source may introduce a measurement error. Wood et al. (31) described a typical cavity blackbody source that exhibits a monotonic drop in emitted radiance (52) with angle. The percentage decrease in radiance from the normal incidence value is 3 to 4% at 45° and 6 to 7% at 70°. Beyond 80°, the falloflf is very rapid due to direct viewing of the cavity wall near the exit aperture of the source. If a Lambertian sample is illuminated with radiance having an angular dependence L 6), where L(0) = 1, then the ratio of the measured reflectance to the true reflectance will be given by... 

FIGURE 2.5. Normalised electroluminescence radiation patterns of die 2-D patterned device measured in die x-(filled circles) and y-directions (filled squares) are shown along with die average of die two (black line, no symbols). The radiation pattern of an unpattemed device is also shown (filled triangles) along with radiation pattern obtained from the lambertian emission (dashed line, no symbols). 

Fig. n.l3 The angular radiation characteristic of the multilayer OLED of the type shown in Fig. 11.9 in comparison to a Lambertian source. The agreement is nearly perfect. 

Initially, we will focus on the mesoscopic description associated with the radiative transfer equation. Then, we will introduce the single-scattering approximation and two macroscopic approximations the PI approximation and two-flux approximation. AH of these discussions are based on the configuration shown in Fig. 6. Collimated emission and Lambertian emission wiU also be considered in the discussion later they correspond to the direct component and the diffuse component of solar radiation, respectively. Throughout our study, the biomass concentration Cx is homogeneous in the reaction volume V (assumption of perfect mixing), and the emission phenomena in V are negligible. The concentration Cx is selected close to the optimum for the operation of the photobioreactor the local photon absorption rate. 4 at the rear of the photobioreactor is close to the compensation point A.C (see Section 5 and chapter Industrial Photobioreactors and Scale-up Concepts by Pruvost et al.). 

Reflectance spectroscopy concerns the measurement of four distinct types of materials and their interaction with light. Specular materials reflect the predominant amount of radiation at an angle equal and opposite to the incident radiation. Diffusely reflective materials scatter light over a wide range of angles, with the perfectly diffuse (or Lambertian) scatterer exhibiting a cosine response to the incident radiation. Gonioapparent... 

Seeliger (in 1888) derived a diffuse reflectance law based on the assumption that the radiation striking the surface of a powder will penetrate into the interior of the powder sample and thus does not represent a perfect remitting (Lambertian) surface (Fig. 6). 

For 2nlQ mode reflectometers, an inverted CPC can be used in front of cavity radiation sources (46, 54) in order to reduce the non-Lambertian properties of such sources at larger angles. The HDR 100 hemiellipsoidal reflectometer from Surface Optics Corporation uses a reflective cone above a cavity radiation source (55). 

Some radiation reflected from the sample in the Bjln mode may be lost out of the entrance port when external optics are used or off of the focusing mirror or lens and its support structure when internal optics are used. This effect can result in an error in the measured reflectance. Similarly, for 2nl6 mode reflectometers, the optics used to collect reflected radiation from the sample reduces the radiant power striking the sample and may affect the measured reflectance. If the sample is a Lambertian reflector and the illumination (0/27i) or viewing (2ti/0) is near normal, then the fraction of radiation intercepting the sample optics is given by... 

The effective reflectance of the detector can be further reduced by using Paschen s (11) method. In particular, an inverted CPC, when positioned in front of a detector (9/2it) or source (2ti/0) to reduce variations from ideal angular response as described in Section V,C, will also enhance the effective absorptance. Radiation reflected from the detector or source at angles larger than the CPC s critical angle is reflected back to the detector or source. If the detector or source is a Lambertian reflector and if the illumination of the CPC is Lambertian, then the effective reflectance of a CPC-detector combination is given by... 

Figure 2.4 shows some types of refractive microlenses that can be fabricated utilizing the standard microfabrication procedures in materials convenient for the MWIR and LWIR ranges. Most of them are loosely based on the solutions for microlenses used in fiber optics to improve coupling between laser sources and fibers [98]. These immersion lenses were thus intended for the operation with coherent and monochromatic radiation, while most of the microlenses in the field of IR detector technology are intended for incoherent, mono- or polychromatic Lambertian sources and, of course, they operate in different atmospheric windows. 

On the contrary, if there are clouds, the discrepancy between flie observation and the model is large in general, and the cause of uncertainty is thought to be the contribution of albedo of clouds. When the actinic flux f tot is divided by direct radiation component Fq, and downward and upward diffusive radiation component Fj, and F, respectively, assuming a Lambertian surface i.e. a virtual completely diffusive surface for which radiance is constant being independent of the direction of observation (isotropic scattering),... 

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