Tri Spherical Lens Assembly

The field of the invention is illumination and the invention is particularly concerned with a tri-spherical lens assembly for marine use.

Earlier designs of marine navigation lights were in two forms: One consisted of a fixture with a single continuous lens, the other of a "combined" fixture with a single light source and two or three separate, usually colored, lenses either joined directly together or separated by a relatively thin opaque vertical divider.

The fixture with the continuous lens, by virtue of its uninterrupted arc of visibility, could be designed to emit light over any predetermined horizontal arc simply by adjusting the angle subtended by the lens segment. The combined fixture, however, contains regions at the lens segment junctions that obscure transmission of light at those points. These designs also employed lens dividers, which comprise thin vertical screens projecting radially outward from the junction, that prevented the light emitted from one lens segment from crossing over into the region of visibility of the other lens segment. The crossing was caused by the lamp filament design, which was generally oriented horizontal and perpendicular to the vertical plane passing through the lens junction and the center of the filament.

According to the current state of the art a problem arises with the use of a single vertical filament. This is particularly true with a C-8 filament. This filament orientation is preferred in order to improve the cut-off (reduction of light emission at the ends of the horizontal prescribed arc of visibility) of the fixture. Using this technique to improve cut-off creates the undesirable obscuration at the junctions of the lens segments. The horizontally broad light source no longer exists to negate the obscuring effect of the vertical junctions. It is necessary, then, to control the transmission of light through the respective lens segments in the vicinity of the junctions in order to replace the light obscured by the junction.

Having in mind the limitations of the prior art it is an object of the present invention to avoid the undesirable obscuration at the junctions of lens segments.

This object is achieved by a reshaped optical surface on the affected lens segment in the vicinity of the junction between two adjacent lens segments.

The usual optical system that employs this invention is comprised of a single light source with a vertical filament, multiple lens segments and either a divider or opaque junction region where segments are joined together. The prior art lens segments are usually transmissive plastic of not necessarily uniform thickness throughout, but with both the internal and external surfaces concentric on any given horizontal plane.

According to the present invention the optical surfaces adjacent to the junction are reshaped to progressively refract the rays as they approach the junction area. This is accomplished by changing the optical surface adjacent to the junction so that the normal to the line tangent to the curve and the incident ray at that point form an angle. The effect is that the ray is bent toward the obstruction at the internal air/lens interface. After passing through the lens medium, the ray is again refracted since the ray is no longer normal to the external surface. The result is a ray bent significantly toward the obstruction, due to the additive effects of refraction at both interfaces (internal and external). The modified surface is curved in such a way that at the farthest distance from the obstruction (where the modified surface begins), the normal to the modified surface is coincident with the normal to the unmodified surface. The normal to the modified surface then diverges from the unmodified normal progressively, as the obstruction is approached. This creates a gradual and increasing refraction of rays as the obstruction is approached, thus reducing the effect of a sharp decrease in light emission from the area of the lens segment from which the light has been borrowed. The degree to which the modified surface is reshaped, depends upon the size of the obstruction, the thickness of the lens segment, index of refraction, and the diameter of the lens assembly; and varies from fixture to fixture.

An alternative embodiment of the invention consists of the modification of the external lens surface in the same region. In this case, the normal of the reshaped surface progressively diverges from the unmodified normal in the opposite direction from the divergence obtained by the internal modification. Refraction only occurs at the external lens/air interface, bending the rays toward the obstruction.

The present invention and its departure from the prior art are explained by reference to the appended drawings, wherein:

FIG. 1 is a plan view of a prior art lens system showing a junction between left and right lens segments;

FIG. 2 is a plan view of another prior art lens system showing a vertical divider between the left and right lens segments;

FIG. 3 is a perspective view of the prior art lens system of FIG. 2 showing the vertical divider between the left and right lens segments;

FIG. 4 is a schematic plan view of a prior art lens system showing light rays eminating from a single vertical filament and the region obscured by the lens segment junction;

FIG. 5 is a schematic plan view of the lens system of the present invention having light rays eminating from a single vertical filament with a first embodiment of the reshaped optical system adjacent the lens segment junction shown in solid lines and a second embodiment shown in dotted lines;

FIG. 6 is a detailed schematic plan view of the right lens of the present invention abutting a vertical divider or junction showing the first embodiment;

FIG. 7 is a detailed schematic plan view as in FIG. 6 but showing the second embodiment;

FIG. 8 is a detailed schematic plan view of the present invention showing light rays eminating from a single vertical filament and the refraction of the light rays by the modified surface adjacent the vertical divider or junction; and

FIG. 9 is a perspective view of the first embodiment of the lens system of the present invention.

The state of the prior art is illustrated in FIGS. 1 through 4 wherein right lens segments 2 and left lens segments 4 are separated by junctions formed with a bonding agent 6 or a vertical divider 8.

FIG. 4 shows the light pattern of rays 10 eminating from a single filament light source 12 and the region 14 obscured by the lens segment junction 16.

FIG. 5 shows the present invention with left lens segment 20 and right lens segment 18 separated by junction 22 which causes obscuration. Reshaped optical surfaces 24 and 26 having repositioned optical radii 28 and 30 respectively cause typical light rays 32 and 34 eminating from single filament light source 36 to refract at surfaces 24 and 26 and converge at point 38. The radius of lens segments 18 and 20 is designated 40. The second embodiment for reshaping the lens system is shown by the dotted lines indicated at 42.

The principles involved in the present invention are explained with reference to FIGS. 6 and 7. With the light source 36 positioned at the center of the circles formed by the concentric internal unmodified surface 43 and the external unmodified surface 44 of the lens segments, a line tangent to the surfaces is always perpendicular to the incident ray emitted by the source, thus the ray is not refracted horizontally by the lens segment, since the incident ray is within a plane normal to the inside and outside surfaces. Considering horizontal refraction only (as the lens assembly may be designed to collimate or diverge the beam in the vertical plane), the law of refraction (Snell's Law) can be applied thus: n.sub.1 sin i=n.sub.2 sin r where:

n.sub.1 is the index of refraction of the first medium,

i is the angle the incident ray forms with the normal to the surface,

n.sub.2 is the index of refraction of the second medium, and

r is the angle the refracted ray forms with the normal to the surface.

In the above equation, the value of i equals 0.degree. for the incident ray; sin i equals 0 and regardless of the values of the indices of refraction, sin r equals 0 and consequently r equals 0.degree.. With no horizontal refraction of the rays, any vertical obstruction in the lens assembly causes obscuration of a corresponding segment within the desired arc of visibility of the fixture. This is the case with the vertical obstruction 46 at the junction of two lens segments.

In order to avoid this obscuration condition, the optical surfaces 24 and 42 adjacent to the junction are reshaped to progressively refract the rays as they approach the junction area. This is accomplished by changing an optical surface adjacent to the junction so that the normal 48 to the line tangent to the curve and the incident ray 50 at that point form an angle (i). The effect is that the ray is bent toward the obstruction at the internal air/lens interface. After passing through the lens medium, the ray is again refracted since the ray is no longer normal to the external surface. The result is a ray 52 bent significantly toward the obstruction, due to the additive effects of refraction at both interfaces (internal and external). The modified surfaces 24 and 42 are curved in such a way that at the farthest distance from the obstruction (where the modified surface begins), the normal 48 to the modified surface is coincident with the normal to the unmodified surface. The normal to the modified surface then diverges from the unmodified normal progressively, as the obstruction is approached. This creates a gradual and increasing refraction of rays as the obstruction is approached, thus reducing the effect of a sharp decrease in light emission from the area of the lens segment from which the light has been borrowed. The degree to which the modified surface is reshaped, depends upon the size of the obstruction, the thickness of the lens segment, index of refraction, and the diameter of the lens assembly; and varies from fixture to fixture.

In the second embodiment of the invention the modification is to the external lens surface in the same region as shown in FIG. 7. In this case, the normal of the reshaped surface progressively diverges from the unmodified normal in the opposite direction from the divergence obtained by the internal modification. Refraction only occurs at the external lens/air interface, bending the rays toward the obstruction.

The preferred method of creating the modified internal optical surface (shown in FIG. 8) is to locate a new construction center (for the modified surface) that is offset from the center of the unmodified lens surfaces, and located at the intersection of two lines, one of which is defined by the point 36 of the unmodified lens surface center and the point 56 where the modified surface begins to diverge from the unmodified surface; and the other at 54 which is defined as the normal of the modified surface where the modified surface joins the obstruction. Creating the modified external surface is accomplished by locating the construction center at the intersection of two lines, one of which is normal to the external lens surface at the point where it is desired that the normals to the modified and unmodified surfaces are to begin to diverge; the other of which is the normal to the modified surface where the modified surface joins the obstruction. In both internal and external modification embodiments, the normals adjacent to the obstruction are calculated by application of the law of refraction with respect to the desired degree of refraction to negate the obscuration of rays by the obstruction.

In FIG. 8 the internal surface 43 has a radius R.sub.1, the external surface 44 has a radius R.sub.2 and the modified surface 24 has a radius R.sub.3. The origin 58 of the radius R.sub.3 is offset a distance 60 from point 36 of the light source.

In a best mode of carrying out the invention R.sub.1 =0.681, R.sub.2 =0.776, R.sub.3 =0.577, and distance 60=0.103.

FIG. 9 shows the light source 36, right lens segment 18 and left lens segment 20 having modified surfaces 24 and 26 joined at 22.

The junction 22 can be constructed as follows:

(a) A lens divider junction which employs an opaque vertical shield that extends radially outward from the assembly; and

(b) A lens segment junction which is caused when two lens segments are physically joined together. A region is created on both sides of the junction where the bonding agent or process (chemical, ultrasonic, etc.) results in the inability of this area to transmit light through the region. The mating edges produced by ordinary tooling (such as injection molding) generally are imprecise enough to produce an obscuring junction at least as wide as the emitting surface of the filament in the light source. To a distant observer of the lighted assembly, undesirable eclipse of the filament by the junction is observed.