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Electrical Compensation of SELFOC Lens Characteristics

IP.com Disclosure Number: IPCOM000047168D
Original Publication Date: 1983-Oct-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Laff, RA: AUTHOR [+2]

Abstract

Three methods for compensating for the roll-off of light intensity caused by the characteristics of a SELFOC* (self-focusing) lens are described. In linear arrays of light-emitting diodes (LEDs), the radiated energy is projected onto a utilization medium using a SELFOC lens. Due to the lens characteristics, the outside row of LEDs in the array will project about 8% less light onto the medium. Combined with a 2.5% ripple variation, the result can be more than a 10% loss at the outside rows. Some applications require a closer tolerance on light intensity across the array. A first way to control the variation across the array is to use a film with an image pattern to filter out the nonuniformities across the array. This approach, however, results in additional power dissipation to compensate for the filter losses.

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Electrical Compensation of SELFOC Lens Characteristics

Three methods for compensating for the roll-off of light intensity caused by the characteristics of a SELFOC* (self-focusing) lens are described. In linear arrays of light-emitting diodes (LEDs), the radiated energy is projected onto a utilization medium using a SELFOC lens. Due to the lens characteristics, the outside row of LEDs in the array will project about 8% less light onto the medium. Combined with a 2.5% ripple variation, the result can be more than a 10% loss at the outside rows. Some applications require a closer tolerance on light intensity across the array. A first way to control the variation across the array is to use a film with an image pattern to filter out the nonuniformities across the array. This approach, however, results in additional power dissipation to compensate for the filter losses. A second method to provide better uniformity across the array is to design the LED driver circuits so that the inside rows of LEDs are turned off for approximately 8% of the time. Like the first method described above, this results in wasted power dissipation since the LEDs must be driven harder to produce a given output level. A third, preferred method is to design the driven circuits so that the outer rows of LEDs receive about 6% more current drive than the inner rows. This will cause the outside LEDs to produce about 8% more luminosity, and there would be no unnecessary dissipation wasted in overdr...