Patent Number: 047926929
Section: description

The lamp 10 shown in the drawing includes a substantially point-shaped source of radiation 11 disposed at one focus of an ellipsoidal reflector 12. The lamp 10 produces a convergent beam of radiation the angle .alpha.E of which measures about 30.degree. with respect to the optical axis 13. At or close to the second focus of the reflector 12, the entrance surface 14 of an optical waveguide 15 is dispoeed. The optical axis of the waveguide 15 at the entrance surface 14 coincides with the optical axis 13 of the reflector 12. The waveguide 15 has a crowned exit surface 16, a bent portion 17 of constant diameter close to the exit surface 16, and a portion 18 having a steeper tapering than exists between the entrance surface 14 and the bent portion 17. The portion 18 is disposed immediately before the exit surface 16. The optical waveguide 15 has an overall conical shape of circular cross-section with the following dimensions: ______________________________________ diameter d1 of the entrance surface 14: 10 mm diameter d2 of the exit surface 16: 3 mm length of the waveguide measured along approx. 100 mm its optical axis: length of the straight portion of the approx. 75 mm waveguide between the entrance surface 14 and the beginning of the bent portion 17: diameter of the waveguide in the bent 4 mm portion 17: radius of the center line of the bent 20 mm portion 17: angle of curvature: approx. 75.degree. length of the portion 18 of steeper 5 mm tapering, within which the dia- meter decreases from 4 mm to 3 mm: ______________________________________ The waveguide 15 is made of quartz having a refractive index of approximately 1.46, which approximately equals .sqroot.2. The waveguide may be formed as a solid rod or composed of a plurality of discrete radiation conducting fibers. Glass or synthetic material may be used instead of quartz. Given the above values, a beam of radiation incident on the entrance surface 14 at an angle .alpha.E of approximately 22.degree. is transmitted through the waveguide 15 to the exit surface 16 which it hits at the limit angle of total reflection, leaving the exit surface at an angle of 90.degree. with respect to the optical axis. Beams incident on the entrance surface 14 at smaller angles leave the exit surface 16 at correspondingly smaller angles. This results in an overall semi-spherical lobe of radiation from the exit surface 16. Beams incident on the entrance surface 14 within an angular range of approximately 22.degree. to 30.degree. leave the waveguide laterally before reaching the exit surface 16 substantially within that region in which the diameter is smaller than about 3.6 mm. It is therefore preferable to select the entrance angle .alpha.E greater than that value (approximately 22.degree.) at which all radiation is transmitted to the exit surface, thus ensuring that radiation of sufficient intensity is available at the exit surface 16 even under large angles with respect to the optical axis. Since the portion 18 disposed immediately before the exit surface 16 has a steeper tapering than the remaining waveguide, any radiation which does not reach the exit surface 16 will leave the waveguide very shortly before the same, thereby enhancing the useful radiation in case the rod is laterally applied. If the ratio of the refractive index of the optical waveguide to that of the environment has the above value of .sqroot.2, any beam carried by the waveguide will reach the exit surface 16, and the largest exit angle will be 90.degree.. With a smaller refractive index ratio, the maximum exit angle will be smaller than 90.degree.. If, in this case, the angle of incidence .alpha.E is increased, radiation will be emitted from the peripheral wall of the waveguide. If the refractive index ratio is made greater than .sqroot.2 part of the radiation transmitted through the waveguide will be totally reflected at the exit surface 16; while this may be avoided by reducing the angle of incidence .alpha.E, a corresponding portion of the radiation emitted by the lamp 10 will be lost, or th ellipsoidal reflector 12 must be shaped so that it surrounds the source of radiation 11 more completely with the result that the reflector must have a greater axial length, thereby incressing the overall dimension of the lamp 10. If the exit surface 16 is made planar, in contrast to the above-described embodiment, it will be seen that the radiation intensitydecreases and a dark zone is produced in a range of about 85 to 90.degree. with respect to the optical axis. This dark zone is avoided by the crowned or rounded shape of the exit surface 16.