A lighting unit including a light-reflecting reflector, a plurality of cold cathode tubes disposed inside the reflector and an optical waveguide connected with an open end of the reflector to guide the light emitted by the cold-cathode tubes. The reflector has a reflective surface that reflects the light having been emitted by the cold-cathode tubes in the direction nearly perpendicular to the wall of each tube, and only in a direction in which the light reflected does not re-enter the cold-cathode tubes. In another embodiment, the lighting unit may include a second optical waveguide disposed in the space between the cold-cathode tube and the reflector, wherein a space is formed between the cold-cathode tube and the second optical waveguide.
1. A lighting unit comprising:
a light-reflecting reflector;
a plurality of cold-cathode tubes disposed inside the reflector; and
an optical waveguide connected with an open end of the reflector to guide the light emitted by the cold-cathode tubes;
wherein the reflector has a reflective surface that reflects the light having been emitted by the cold-cathode tubes in the direction nearly perpendicular to the wall of each tube, and only in a direction in which the light thus reflected does not re-enter the cold-cathode tubes; and
further wherein the reflective surface includes at least three adjacent concaved curve segments, with each of the adjacent concaved curve segments having a curvature center and a constant radius, with the constant radius of at least one of the concaved curve segments being different from the constant radius of at least one other concaved curve segment.
2. The lighting unit as claimed in claim 1 , wherein the reflective surface is so disposed that the surface reflects the emitted light at an angle at which the reflected light runs through the space between the cold-cathode tube and the reflector adjacent thereto or between the neighboring cold-cathode tubes.
3. The lighting unit as claimed in claim 1 , wherein the reflective surface is so disposed that the surface reflects the light emitted by one cold-cathode tube at an angle at which the reflected light runs through the space between the one cold-cathode tube and the other cold-cathode tube and that the surface reflects the light emitted by the other cold-cathode tube at an angle at which the reflected light runs through the space between the one cold-cathode tube and the wall surface of the reflector.
4. The lighting unit as claimed in claim 1 , wherein the plurality of concaved curve segments include a first set of segments with a first constant radius and a second set of segments with a second constant radius, where the second constant radius is different from the first constant radius.
5. The lighting unit as claimed in claim 4 , wherein the first set of segments are symmetrically arranged with respect to upper and lower sides of the reflector, and the second set of segments are also symmetrically arranged with respect to the upper and lower sides of the reflector.
6. A lighting unit comprising:
a light-reflecting reflector;
a cold-cathode tube disposed inside the reflector;
a first optical waveguide connected with the open end of the reflector for guiding the light emitted by the cold-cathode tube; and
a second optical waveguide disposed in the space between the cold-cathode tube and the reflector and having two ends that both face an end of the first optical waveguide,
wherein a space is formed between the cold-cathode tube and the second optical waveguide.
7. The lighting unit as claimed in claim 6 , wherein the profile of the surface of the second optical waveguide that faces the outer surface of the cold-cathode tube is analogous to the profile of the outer surface of the cold-cathode tube.