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Proceedings Paper

Impact of light coherence on depth of focus of wearable retinal displays
Author(s): Marc von Waldkirch; Paul Lukowicz; Gerhard Troester
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Paper Abstract

This paper discusses the impact of light coherence on the defocusing properties of a novel retinal projection display. The display is based on a liquid crystal display (LCD) illuminated by partially coherent light from a LED which projects the LCD-image directly onto the eye's retina. It is shown that the increase of the coherence level of the illumination light enhances on the one hand the contrast of a defocused image. On the other hand, however, the perceived image quality is affected by the occurrence of intermediate defocusing peaks as well as by coherence effects, such as edge-ringing. Measurements of both the modulation transfer function (MTF) and of the text readability when defocusing are presented using a bench model of the display system. The experimental results reveal that for text readability the best DOF can be achieved not for fully coherent illumination, but for partially coherent light of a coherence level σ ≈ 0.35-0.5. Further, it is shown that the optimum σ-level depends slightly on the targeted text size.

Paper Details

Date Published: 12 November 2003
PDF: 10 pages
Proc. SPIE 5186, Design of Efficient Illumination Systems, (12 November 2003); doi: 10.1117/12.505814
Show Author Affiliations
Marc von Waldkirch, ETH Zurich (Switzerland)
Paul Lukowicz, ETH Zurich (Switzerland)
Gerhard Troester, ETH Zurich (Switzerland)

Published in SPIE Proceedings Vol. 5186:
Design of Efficient Illumination Systems
R. John Koshel, Editor(s)

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