Light source using large area LEDs
A printing apparatus ( 100 ) for printing digital images onto a photosensitive medium ( 140 ) employing, for exposure energy, a light source ( 20 ) that uses various arrays of LEDs ( 32 ). The printing apparatus ( 100 ) may form the print image using sequential modulation, one color at a time, or by applying all colors simultaneously. Arrangements of discrete LEDs ( 32 ) may include high-intensity devices configured with collector cones ( 41 ) arranged as a multicone structure ( 141 ), with parabolic reflectors ( 65 ), or collimating lenses ( 36 ). Large area LEDs ( 46 ) may alternately be used, arranged on an angled mounting surface ( 64 ), for example.
1. An improved light source for providing an illumination beam along an illumination axis, comprising:
(a) a plurality of large area LEDs, mounted on a base, for generating emitted light;
(b) a collector structure for collecting said emitted light from said plurality of large area LEDs to form the illumination beam, the collector structure comprising:
for each LED, a light guide for collecting, at an input, said emitted light received from said LED and directing said emitted light to an output, along said illumination axis, said light guide comprising:
(i) a collimating element near said input for collimating a portion of said emitted light to direct collimated light in the direction of said illumination axis;
(ii) a guide element for directing some of the other said emitted light at said input to said output and along said illumination axis; and
wherein, said output of at least a first said light guide has at least one flat edge for butting against said output of at least a second said light guide.
2. An improved light source according to claim 1 wherein said large area LEDs have more than one color.
3. An improved light source according to claim 1 wherein said light guides are cone segments, narrower at the input end.
4. An improved light source according to claim 1 wherein said light guides are fabricated from glass or plastic.
5. An improved light source according to claim 1 wherein said base is curved.
6. An improved light source according to claim 1 wherein said base comprises a plurality of angled surfaces.
7. An improved light source according to claim 1 further comprising at least one additional LED not having a corresponding light guide.
8. A method for forming a collector structure for directing illumination from a plurality of LEDs along an illumination axis, the method comprising:
(a) providing, for each LED, a light guide having an input side for collecting light from the LED and an output side for directing light along the illumination axis, the light guide comprising:
(i) a collimating element for collimating a first portion of the LED illumination incident to said element along the illumination axis;
(ii) a guide element for directing a second portion of the LED illumination along the illumination axis using total internal reflection;
(b) trimming at least two adjacent said light guides along their corresponding said output sides, to provide an abutting edge for said at least two adjacent said light guides.