Patent Application
20080266665
The present invention is generally related to traffic signaling, and more specifically to a lens system adapted to direct light from an array of light emitting diodes (LEDs) in a traffic signal.
In modem traffic signals it is desirable to signal different traffic lanes and therefore traffic signals are required to independently send out signal light. In addition for power efficiency and cost reduction the new bright LEDs are being used. To make efficient use of the light from an LED array it is necessary to use a lens, typically a Fresnel lens, so that light can be collimated and sent to the street as shown in
However this lens system is not the most efficient system and for large off axis viewing distances it appears partially illuminated with a bow-tie type of pattern when the traffic signal is on.
The present invention achieves technical advantages as a traffic light compound lens system. One embodiment of the invention utilizes two Fresnel lenses to provide a more efficient lens system with better light directing capabilities than a single lens system. Advantageously, the optical power of each Fresnel lens is less than that required for the single lens system. Due to aberration reduction, the compound lens system has less geometrical aberration than a single lens system, especially over a larger field of view.
Referring to
Referring now to
Advantageously, the optical power of each Fresnel lens 202 and 204 is less than that required for a single lens system 100. Additionally, because of aberration reduction the compound lens system 200 mitigates geometrical aberration better than a single lens system, especially over a larger field of view. Moreover, first Fresnel lens 202 can act as a collector and direct light toward second Fresnel lens 204 so that a miniscule amount of light from the LED array 104 is wasted. This is especially true for off-axis LEDs. Both Fresnel lenses 202 and 204 have a positive focal length. The focal length of first and second Fresnel lenses, 202 and 204 respectively, are in the range of ratios 1/3 to 3. In one exemplary embodiment, first Fresnel lens 202 has a focal length of approximately 8 inches and second Fresnel lens 204 has a focal length of approximately 12 inches. The compound lens system 200 is nearly telecentric in the LED space.
To improve the light filling, or how it appears illuminated from the viewer's standpoint, light scattering or diffusing surface 206 can be added to the compound lens system 200. In one exemplary embodiment, light scattering or diffusing surface 206 is operably positioned in a plane between LED array 104 and first Fresnel lens 202 to improve light distribution. In a second exemplary embodiment, light scattering or diffusing surface 206 is operably coupled to the first Fresnel lens 202. In a third exemplary embodiment, light scattering or diffusing surface 206 is operably positioned in a plane between first Fresnel lens 202 and second Fresnel lens 204. In a fourth exemplary embodiment, light scattering or diffusing surface 206 is operably coupled to the second Fresnel lens 204. In a fifth exemplary embodiment, light scattering or diffusing surface 206 is operably coupled to the LED array 104.
Though the invention has been described with respect to a specific preferred embodiment, many variations and modifications will become apparent to those skilled in the art upon reading the present application. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.
