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KEYBOARD LIGHTING BY ABUNDANT FLUX OF THE LCD DISPLAY BACK LIGHT

IP.com Disclosure Number: IPCOM000013434D
Original Publication Date: 2000-May-01
Included in the Prior Art Database: 2003-Jun-18
Document File: 2 page(s) / 106K

Publishing Venue

IBM

Abstract

KEYBOARD LIGHTING BY ABUNDANT FLUX OF THE LCD DISPLAY BACK LIGHT Abstract It is possible to use excess light of a LCD back light for illuminating a keyboard instead of an additional light source. At the edge of the back light guide, intensity is very high, but the flux of those light are not used efficiently. Detail of Invention During keyboard operation of the notebook PC in a dark, a keyboard is too dark to identify its key top nomenclature, but required luminosity for the keyboard operation is not so much. A few luxe is enough. Assuming a cold cathode fluorescent lamp has L [nt] surface intensity, and an aperture with w [m] width l [m] length leaks light flux, then the surface luminosity E [lx] at keyboard with d [m] width located h [m] below from the center of the aperture, (see Figure 1)

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KEYBOARD LIGHTING BY ABUNDANT FLUX OF THE LCD DISPLAY BACK LIGHT Abstract

It is possible to use excess light of a LCD back light for illuminating a keyboard instead of an additional light source. At the edge of the back light guide, intensity is very high, but the flux of those light are not used efficiently.

Detail of Invention

During keyboard operation of the notebook PC in a dark, a keyboard is too dark to identify its key top nomenclature, but required luminosity for the keyboard operation is not so much. A few luxe is enough. Assuming a cold cathode fluorescent lamp has L [nt] surface intensity, and an aperture with w [m] width l [m] length leaks light flux, then the surface luminosity E [lx] at keyboard with d [m] width located h [m] below from the center of the aperture, (see Figure 1)

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Figure 1

     wlE = L %(h2+d2) % h h2+d2 . To get E=1 [lx] from an aperture w=1 [1 mm] by l=200 [mm] at d=200 [mm] and h =20 [mm] , the surface intensity of the lamp L is less than 2,000 [nt]. To condense the leakage flux efficiently, locating the lamp at a focal point of a short focus lens makes a parallel flux. Also light beam can be shaped any width and directed to any direction if a convex curvature of the lens is formed appropriately. Since LCD back panel is thin, it is very difficult to use regular lens. A Fresnel lens or lens array with short focus small lenses can be used.

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