A typical "white" LED comprises a blue source and one or more phosphors, which down-convert the high energy blue light to longer wavelengths. The resultant "mixture" of wavelengths (predominantly residual blue light from the source and yellow and red from the phosphors) produces white light. Typically, phosphors are coated directly (proximally) onto the blue source. This work differs from the conventional approach by incorporating phosphors in a secondary optic, which is remote from the source. This has the advantages of being able to recover the source LED and to change the output wavelength by stacking optics that contain different levels of different phosphors, or by mixing different phosphors into a single optic. The work has created a range of secondary optics that contain one or more phosphors at relatively low levels of addition (1%-4% by weight) in thermoplastic and thermosetting matrices including polystyrene, poly(methylmethacrylate) and silicone. The phosphors are based on a range of YAGs and nitrides. The secondary optics were manufactured by injection moulding (thermoplastics) or casting (thermosets) and were used singly or in stacked layers to down-convert light from a royal blue (450 nm) LED source to produce a range of "white" light sources. Both injection moulding and casting are relatively inexpensive and commonly encountered processes. The optical performance of these optics was measured by Spectral Power Distribution (SPD), chromaticity, Colour Temperature (CCT) and Colour Rendering Index (CRI). CCT and CRI values ranged from 3000K to 6500K and (80-95) depending on the phosphor composition. Measurements were also carried out on the long-term performance of the secondary optics and these showed little or no change after 24 months continuous and intermittent exposure.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:728008 |
| Date | January 2017 |
| Creators | Makkaoui, Ahmad |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.research.manchester.ac.uk/portal/en/theses/mechanics-and-evaluation-of-integrating-of-remote-phosphors-into-the-secondary-optics-of-luminaires-based-on-high-brightness-leds(33bbfc8b-6921-42a7-a2fe-26bac8939b8f).html |
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