Long lifetime, low intensity light source for use in nighttime viewing of equipment maps and other writings

A long-lifetime light source with sufficiently low intensity to be used for reading a map or other writing at nighttime, while not obscuring the user's normal night vision. This light source includes a diode electrically connected in series with a small power source and a lens properly positioned to focus at least a portion of the light produced by the diode.

The present invention relates to light sources; particularly, it relates to 
long-lifetime light source with sufficient low intensity so as to be used 
for nighttime reading of maps and documents without obscuring the user's 
normal night vision. 
One device in the prior art, which is related to the subject invention, 
uses a prism to project light of a desired color onto an object, as 
described in U.S. Pat. No. 1,810,669 to Loeb. Another known device 
discloses a flashlight which passes only light of shorter wavelengths by 
using a filter, as described in U.S. Pat. No. 2,304,742 to Officer et al. 
Another known prior art device discloses a filter arrangement for a 
photographic flash that uses only infra-red light, is described in U.S. 
Pat. No. 2,342,470 to Hunt. Still another prior device discloses a 
combination writing instrument, as described in U.S. Pat. No. 4,168,521 to 
Bajusz. There is a need at present for a device to read maps and other 
writings at nighttime without obscuring the user's normal night vision. 
For example, a person driving a car during the night may use such an 
invention to read a road map. 
This and other unique problems require a low intensity visible light 
focused very closely to the map or writing to be examined. 
It is, accordingly, a general object of the invention to provide a 
long-lifetime light source with sufficiently low intensity. 
Another object of the invention is to provide a light source with a lens 
having a suitable focal length to allow it to be used close to a map or 
writing to be examined. 
Other objects, advantages and novel features of the invention will be 
apparent to those of ordinary skill in the art upon examination of the 
following detailed description and the accompanying drawing of a preferred 
embodiment of the invention. 
SUMMARY OF THE INVENTION 
The invention comprises a light source for nighttime use, which includes a 
power source, a light-emitting diode connected electrically to that source 
in a circuit and chosen to produce a visible wavelength light in response 
to the flow of a small support across the diode and a lens with suitable 
focal length positioned adjacent to the diode to focus a portion of the 
light produced by the diode. 
An important difference between the invention and the devices of the prior 
art is the use of a light-emitting diode in a simple arrangement. This 
invention has the advantage of providing a long-lifetime light source with 
a very low intensity. Another advantage of the invention is that the 
lifetime of the light source may be increased by controlling the current 
flow across the diode with a small resistor connected in the battery-diode 
circuit.

DESCRIPTION OF A PREFERRED EMBODIMENT 
Reference will now be made in detail to the preferred embodiment of the 
present invention, example of which is illustrated in the accompanying 
drawing. 
While the invention will be described in connection with a preferred 
embodiment, it will be understood that it is not the intention to limit 
the invention to that embodiment. On the contrary, it is intended to cover 
all alternatives, modifications and equivalents, as may be included within 
the scope of the invention defined in the appended claims. 
Referring to the drawing, a small power source 11, such as a three-volt 
battery (or two 11/2 volt penlight batteries in series) is connected in 
series with a conventionally known diode 12 to produce a low intensity 
visible light 15. The light 15 may be in a desired light spectrum range, 
for example red. This light 15 will be produced in response to the passage 
of current, approximately 25 milliamperes, across a light-emitting diode 
12. To focus and direct at least a portion of the light produced by diode 
12, a lens 13 is properly positioned adjacent to diode 12 to produce a 
light beam 16. Lens 13 may have a focal length of 1 to 2 centimeters in 
order to direct the light beam 16 close to a map or other writing, 
indicated as 17, to be examined. The lifetime of the power source 11 is 
about twenty to twenty-five hours with constant use and about forty hours 
if used intermittently. The current flow across diode 12 may be reduced or 
controlled by including a small variable resistor 14 in series with diode 
12 and power source 11. However, this will reduce the intensity of the 
light 15 produced by this invention. 
The foregoing description of a preferred embodiment of the invention has 
been presented for purposes of illustration and description and is not 
intended to be exhaustive or to limit the invention to the precise form 
disclosed. The embodiment was chosen and described in order to best 
explain the principles of the invention and their practical application to 
thereby enable others skilled in the art to best utilize the invention in 
various embodiments and with various modifications as are suited to the 
particular use contemplated.