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The transmitting characteristics of high-transparency double-layer metallic meshes with submillimeter period were analyzed using an analytical model, which was established using angular spectrum propagation theory and verified through experiments. It was found through analysis that rotating misalignment has significant effect on the distribution of diffraction spot intensity. Large period and small linewidth can be used to obtain high transmittance and low levels of stray light. Substrate thickness has little effect on transmitting characteristics of mesh, and so it is a variable free to choose in optimizing shielding characteristics of mesh. We think, together with other ways and means of optimizing shielding characteristics of mesh, the model can also be used for the optimization of a high-pass mesh filter. OCIS codes: 350.2460, 050.1970, 220.3740.

An optical-digital method has been developed to obtain the Wigner distribution function of onedimensional complex fields. In this technique an optical setup is employed to experimentally achieve the Radon-Wigner spectrum of the original signal through intensity measurements. Digital tomographic reconstruction is applied to the experimental spectrum to reconstruct the two-dimensional Wigner distribution function of the input. The validity of our proposal is demonstrated with experimental data, and the results are compared with computer simulations. OCIS codes: 070.1170, 100.6950.

Algorithms for selecting LEDs to imitate a group of daylight spectra, instead of fixed-spectrum lighting, are based on minimizing two indices. The first index related to the LEDs only is minimized for determining LED candidates. Minimizing the second index obtained by applying the daylight spectra to the candidates achieves a minimax solution. The sum of the second indices of the daylight spectra can be well approximated by that of the average spectrum of the daylight spectra and is treated as a target spectrum for the LED selection. A pruning process is followed to delete redundant LEDs. OCIS codes: 230.0230, 230.3670, 070.4790, 300.6170.

The average spectral power distribution of a set of measured daylight spectra, [E.sub.av] ([lambda]), is used for preliminary screening to select optimal sensor sets for daylight recovery. Spectra quite different from [E.sub.av] ([lambda]) are applied to the screened sets to obtain minimum total spectral error, which is closely related to recovery metrics but not to the coefficient of error. All basis functions should be utilized to make these two errors equal, to predict precisely the best sensor set, and to extend a set of few sensors to a set of many sensors. These are not acquirable by an exhaustive full search method. OCIS codes: 120.0280, 120.6200.

The technique used by Leonardo da Vinci to paint flesh tints--the sfumato--has never been scientifically depicted until now. From 100,000,000 reflectance spectra recorded on Mona Lisa, a virtual removal of the varnish is first obtained. A unique umber pigment is then identified in the upper layer and an exceptional maximum of the color saturation is underlined, both characteristics of a glaze technique. The modeling calling upon the radiative transfer equation confirms this maximum of saturation, the identification of an umber in the upper layer, and moreover underlines a mixture of 1% vermilion and 99% lead white in the base layer. Finally, the modeling, using the auxiliary function method, explains the spectacular maximum of saturation by the multiple scattering. OCIS codes: 300.6550, 110.4234, 030.5620, 290.4210, 330.1690.

The SMARTS spectral model can advantageously be used to predict clear-sky irradiance spectra on surfaces of any tilt and orientation, e.g., for the simulation of spectrally selective technologies like photovoltaic devices or coated fenestration systems. To evaluate the intrinsic accuracy of the model, its current version undergoes here a three-step validation exercise, involving reference radiative transfer codes, and two series of sophisticated spectral and ancillary measurements performed at different locations. Provided that the most important inputs are known with sufficient accuracy, it is concluded that the model performance is very high, with typical differences of 1-2% when compared to reference models, and uncertainties largely within the overall experimental error ([approximately equal to]5%) when compared to spectroradiometric measurements. The effect of imprecise spectral reflectance data of the foreground on the diffuse irradiance incident on shaded vertical surfaces is discussed. Keywords: Irradiance; Spectral; Solar radiation; Spectrum; Validation; Model; Atmosphere; Spectroradiometer; Spectrometry; Direct irradiance; Diffuse irradiance

An analytical solution to the attenuation of flux within an integrating sphere due to spherical integrating source coating, exit port escape, and atmospheric absorption is derived employing a geometric probability distribution of completed sphere transits. This is used to determine the mean number of completed sphere transits and its variance. Equations that provide the attenuation ratios for the three extinction mechanisms are derived using the energy balance and summation of refection methods. The mean length of a transit of the sphere and its variance are presented and used to derive expressions for the mean and variance of photon path lengths in the sphere. OCIS codes: 000.4430, 120.0280.