Lamp Filament Configuration for Use in a Drum Lens

Navigational lights utilizing drum lenses are being required to have increasingly greater light outputs. However, there is a maximum practical optical output which can be radiated from a unit of filament surface. In addition, vertical beam spread of light from an ideal drum lens is in direct proportion to the length or height of the lamp filament and high intensity lamp filaments often exceed the minimum length resulting in beam divergencies in an excess of the minimum value required. These problems can be overcome to some extent by utilizing multiple short filaments for increasing the optical output and narrowing the beam of light from the lens.

However, multiple filaments introduced problems of their own. One of the problems of multiple filaments is caused by shadowing. That is, it is desired to maintain an optical output from the lens in a wide horizontal direction, and therefore some of the filaments will be aligned with other filaments causing shadowing or reducing of the light output in the direction of aligned filaments. Furthermore, with a multiplicity of filaments, the filaments will not be positioned on the focal point of the drum lens thereby causing defocusing of the light and consequent undesirable beam spreading.

The present invention is directed to an improved lamp filament configuration for use in drum lenses of a navigational light in which the filaments are positioned to reduce filament shadowing and defocusing, and provide increased light output with a minimum of power.

The present invention is directed to a filament system in a lamp for use in a drum lens of a navigational light in which at least four vertically positioned similar filaments are spaced about but away from a vertical axis adapted to be placed at the focal point of the lens. The filaments are positioned in a horizontal plane relative to each other whereby no more than two filaments are aligned in any horizontal direction thereby reducing filament shadowing.

Still a further object of the present invention is the provision of a lamp filament configuration having at least four filaments in which the vertical height of the filaments is limited, such as approximately ten millimeters, thereby limiting beam spread from the lens.

Still a further object of the present invention is the provision of a multiple filament system for a lamp having four vertically positioned similar filaments in which three of the filaments are positioned at the corners of a horizontal square in which the center of the square is adapted to be placed at the focal point of a drum lens. The fourth filament is positioned outside of the unoccupied corner of the square in line with the diagonal of the square through the unoccupied corner thereby minimizing shadows of one filament by other filaments in any horizontal direction.

Yet a further object of the present invention is the sizing of the sides of the square at a minimum, such as approximately ten millimeters, thereby positioning the filaments as close as practical to the center of the square for minimizing defocusing and wherein the fourth filament is positioned approximately three millimeters from the unoccupied corner thereby reducing horizontal shadowing between the filaments without undue defocusing.

Other and further objects, features and advantages will be apparent from the following description of a presently preferred embodiment of the invention, given for the purpose of disclosure and taken in conjunction with the accompanying drawing.

FIG. 1 is an elevational view of a conventional navigational light having a drum lens in which a lamp utilizing the filament configuration of the present invention is used,

FIG. 2 is an enlarged elevational view of one embodiment of a lamp of the present invention utilizing dual filament systems of the present invention,

FIG. 3 is an enlarged top elevational view of the filament configuration of the dual filament systems of the lamp of FIG. 2,

FIG. 4 is a side elevational view of the dual lamp configurations in the lamp of FIG. 2, and

FIG. 5 is a graph showing the light output of the present invention as compared with a conventional filament.

Referring now to the drawings, and particularly to FIG. 1, the reference numeral 10 generally indicates any navigational light, which may be Model ML-300 of Tideland Signal Corporation, having a base 14 and a drum lens 16 in which a lamp 18 utilizing the present invention is placed at the focal plane 20 of the lens 16.

Referring now to FIG. 2, the lamp 18, preferably includes dual filament systems 22a and 22b embodying the present invention and is mounted on a base 24. One of the filament systems, either 22a or 22b, is positioned at the focus 21 of the drum lens 16 and when the filament in the operating position, such as 22a burns out, the lamp 18 is conventionally rotated to move the other filament system 22b into the operating position at the focal center 21 of the lens 16. The lamp 18 includes electrical contacts 25 and 26 for conducting electricity through electrical conductors 28 and 29 to the filament systems 22a and 22b, respectively.

The present invention is directed to providing a multiple filament system which provides the desired optical intensity, reduces filament shadowing, reduces beam spread, and reduces defocusing. Preferably, referring now to FIGS. 3 and 4, the filament system 22a includes four vertically positioned similar filaments 30a, 32a, 34a, and 36a. Similarly, the filament system 22b consists of filaments 30b, 32b, 34b, and 36b. Preferably, the vertical height of each of the filaments is approximately ten millimeters, as contrasted to standard high intensity lamp filaments in use of thirty millimeters, thereby confining the light beam spread through the lens 16 to a minimum. That is, the vertical beam spread of light from a drum lens 16 is in direct proportion to the length of the lamp filament. Since the maximum practical optical output which can be radiated from a unit of filament surface is limited, the use of multiple filaments of minimum lengths allow the provision of the necessary power output, but confines the power output to a narrow beam as required thereby avoiding wasting power. However, the principal problem of using multiple filaments is that the drum lens 16 is required to direct light over a wide range of a horizontal direction, generally at least 270.degree. and therefore the light output in some horizontal directions will be blanketed or shadowed as two or more filaments are aligned in some horizontal directions.

The preferred embodiment of the present invention utilizes four filaments, which is sufficient to provide the necessary power output, and which are positioned in a horizontal plane such that no more than one filament is shadowed as observed in any horizontal direction. Preferably, three of the filaments are arranged at three of the corners of a square such as filaments 30a, 32a, and 34a of system 22a and 30b, 32b, and 34b of system 22b. When in use, the filament system 22a and 22b are alternately positioned with the centers of the square 38a and 38b at the focus 2l of the drum lens 16. The dimensions of the squares are the minimum permitted by practical consideration in order to position the filaments as close to the centers 38a and 38b of the squares and thus on the focus 2l in order to reduce defocusing and consequent beam spreading by the lens 16. The fourth filament, filament 36a in system 22a and filament 36b in system 22b, is placed outside of the unoccupied corner of the square along a diagonal of the square passing through the unoccupied corner and moved outwardly far enough to avoid shadowing when viewed along a direction parallel to the sides of the square. For example, the filaments 36a and 36b are offset from each side of the square adjacent the unoccupied corner approximately two millimeters or approximately three millimeters from the unoccupied corner thereby reducing horizontal shadowing between filaments without causing undue defocusing.

While the outside filaments 36a and 36b could be placed within the squares from a configuration standpoint, this would require that the size of the square be increased thereby increasing the distance of the other filaments from the center of the square and increasing defocusing.

Referring now to FIG. 5, a graph 40 is shown showing the light output from a conventional 1000 watt single thirty millimeter high filament which was operated at a 120 volts and 8.33 amps to provide a power input of 1000 watts. Graph 50 is a graph of the output of one of the filament systems 22a or 22b positioned as shown in FIGS. 3 and 4 at 130 volts and 5.8 amps to provide a power input of 754 watts. Both of the lamps tested on the graphs of FIG. 5 were focused in a Tideland ML-300 HI drum lens and an azimuth scan of 360.degree. was taken. The average light output 42 from the graph 40 was 14,625 cd while the average output 52 from the graph 50 of the present invention was 23,975 cd. Each of the output graphs 40 and 50 had a low point, such as 44 and 54, respectively. The low point 44 in the conventional lamp was due to a large post opposite the single filament which shadowed the filament in one direction. In the case of the graph 50, the lamp tested had dual filament systems 22a and 22b whereby one of the systems would shadow the other at the low output 54. Of course, a single filament system may be used, but often navigational lights only require a horizontal output of approximately 270.degree. and dual systems are desirable for safety. It is to be particularly noted that the present invention provided an increased light output as compared to a standard lamp in addition to using only 754 watts as compared to 1000 watts for the conventional lamp.

The present invention, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned as well as others inherent therein. While a presently preferred embodiment of the invention is given for the purpose of disclosure, numerous changes in the details of construction and arrangement of parts will readily suggest themselves to those skilled in the art and which are encompassed within the spirit of the invention and the scope of the appended claims.