Illumination – Self powered lamp – Flat flashlight casing
Reexamination Certificate
1999-04-12
2001-12-18
O'Shea, Sandra (Department: 2875)
Illumination
Self powered lamp
Flat flashlight casing
C362S157000, C362S184000, C362S800000
Reexamination Certificate
active
06331062
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a portable light, particularly to torches, flashlights and the like.
2. Description of Related Art
Light emitting diodes (LEDs) are well-known as light sources. While more efficient than incandescent light bulbs at converting electrical power to light, LEDs can generally emit only low intensity light. LEDs are widely used as indicator lights or warning lights in instrument panels (e.g., in aircraft or in road vehicles). Recently LEDs have also been used as light sources in bicycle lamps, serving to give warning to other road users of the presence of the cyclist, and in key-ring lights.
LEDs are thus generally used for “passive” illumination, in which light emitted from the LED enters an observer's eye substantially directly, so as to confer information to the observer about the LED (e.g. on or off). It is very uncommon for LEDs to be used for “active” illumination, in which light emitted from the LED encounters an object and is reflected or otherwise re-directed from the object to an observer, so as to give information to the observer about the object rather than the LED. The reason for is the low intensity of light emitted from LEDs, as explained above, and because of the delicate nature of LEDs which are easily damaged, e.g., by exposing the LED to a current and/or voltage which exceeds the maximum values stated by LED manufacturers (“overrunning”) the LED. It is well known to the person skilled in the art that overrunning of LEDs should be avoided because it can cause the LED to burn out or fail, or else substantially shorten the working life of the LED.
SUMMARY OF THE INVENTION
In a first aspect, the invention provides a portable electric light comprising a housing, a source of electrical power, and having as a light source an LED with a high internal resistance (i.e., at a current of ≈50 mA an internal resistance greater than 10 &OHgr;). Preferably the internal resistance of the LED is greater than 11 &OHgr;, more preferably greater than 12 &OHgr;, and most preferably greater than 13 &OHgr;.
The inventor has surprisingly found that an LED with a high internal resistance can be overrun considerably in excess of a manufacturer's stated maximum voltage or current levels without failing and without substantially reducing the working life of the LED. An LED overrun in this way is capable of emitting far more light than is conventional, such that an electric light in accordance with the invention may usefully be employed for active illumination.
Most conventional LEDs have an internal resistance which is too low (e.g., around 9 &OHgr;, at a current of 50 mA) to be useful for use in an electric light in accordance with the invention. However, a number of suitable LEDs are available for use in the light of the present invention. Preferably the LED is one which emits a broad spectrum of wavelengths. Conveniently, the LED emits light which is perceived by an observer as substantially white, or white with a perceptible blue tinge.
The human eye adapts so as to become more sensitive to blue light in the dark, so an electric light which emits at least some light in the blue wavelengths will be perceived by an observer as brighter than visible light of the same intensity of a longer wavelength.
A particularly preferred LED for use in the light of the invention is an LED Model No. NSPW 210AS made by Nichia, 491 Oka, Kaminaka-cho, Ana-shi, Tokushima 774 Japan.
The source of electrical power may comprise an AC input (e.g., from main supply) treated so as to be suitable for use with LEDs (e.g., voltage reduced by, for example, a step-down transformer and converted to a DC current). Preferably the source of electrical power provides a DC output ab initio. This may preferably comprise one or more dry electrochemical cells, such as a button cell or Lithium cell which are well known to those skilled in the art. Either a single cell, or a plurality of cells which may be arranged in series or in parallel, may be provided. Particularly preferred combinations are two or three button cells, used to drive one or two Nichia NSPW 310AS LEDs.
Preferably the electric light of the invention comprises a plurality of LEDs having a high internal resistance. Conveniently two or three such LEDs will be provided, which may be arranged in series, or preferably, in parallel.
Most conveniently, the electric light of the invention takes the form of a hand-held light, such as a torch or flashlight. The small size of the LED light source(s) and the selection of appropriate cells (e.g., Lithium cells) allows for a very compact arrangement which fits comfortably within the palm of a user's hand. In particular, a laterally flattened shape may be preferred, which can readily fit into a trouser or jacket pocket. Alternatively, the light may be provided with mounting means (e.g., a screw or hook), for mounting the light on a surface, such as a wall or shelf, or perhaps a spike for planting in the ground.
It is also preferred that the LED in the light of the invention has a threshold voltage which is higher than that of conventional LEDs. The threshold voltage is a term which is understood by those skilled in the art and refers to the voltage applied across an LED below which very little light is emitted. For most conventional LEDs, the threshold voltage is typically around 2 volts. In contrast, for LEDs of use in the light of the invention, the threshold voltage will preferably, but not essentially, be about 3 volts or higher.
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Hobden David V.
O'Shea Sandra
Price and Gess
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