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Supplemental lighting is necessary for winter greenhouse tomato production, and optimised spectra must consider both yield and energy use. In a 20-week winter greenhouse experiment, two common commercial tomato cultivars–‘Merlice’ and ‘Brioso’–were grown under four LED spectra with 38%, 63%, 81%, and 95% red photons. As the percentage of red photons increased, the blue and green percentages decreased (not at the same ratio). Stem length, specific leaf area, and dry mass partitioning were not significantly affected by spectra in either cultivar, but increasing the red percentage from 38% to 95% decreased harvested fruit fresh mass by 13%, total plant dry mass by 7.1%, and fruit dry mass by 9.5% in ‘Merlice’. There were no significant differences in these parameters for ‘Brioso’. The yield kWh−1 increased with increasing percent red in both cultivars because LED fixtures with higher fractions of photons from 660 nm red LEDs have higher photon efficacies (µmol J−1). The efficacies of the lamps in this study were estimated to range from 2.6 to 3.6 µmol J−1. Growers must consider tradeoffs that can occur between yield and efficacy in some cultivars, and how these factors apply to their situation, when choosing the spectrum for their greenhouse.

This thesis is divided into three parts. In the first, some aspects of the theory and methods of X-ray Crystallography are introduced and briefly discussed. The second and final parts are concerned with the applications of these methods in the elucidation of the crystal structures of four molecules. Accounts of the structural analyses of triphenyl-bismuth, (C6H5)3Bi, and triphenylbismuth dichloride, (C6H5)3BiCl2, are contained in Part II. It has been established that the triphenylbismuth molecule is pyramidal with virtually no hybridisation of the 6s and 6p orbitals of the bismuth. The expected symmetry has been destroyed by the asymmetric rotations of the phenyl groups about the Bi-C bonds. The proposed trigonal bipyramidal structure for triphenylbismuth dichloride has been confirmed by a crystal-structure analysis. The more electronegative chlorine ligands occupy the apical positions with the phenyl groups attached equatorially to the central bismuth atom. Again the molecule possesses no overall symmetry as a result of the unequal rotations of the benzene rings with respect to the equatorial plane. Part III describes the analyses of two caryophyllene rearrangement products, viz., caryophyllene 'iodonitrosite' and the mono-p-bromobenzenesulphonyl ester of the diol derived from pseudoclovene-A. The former belongs to the relatively new class of stable aliphatic nitroxide radicals, and has an N-O bond length of 1.308 A which corresponds to a three-electron bond. The absolute stereochemistries of both derivatives have been established by means of Bijvoet's anomalous dispersion method. Fairly detailed accounts of the conformations of these molecules are given and the ways in which they have undergone distortions, to avoid the severe inherent strain associated with these species in their classical conformations, are discussed.