There is a need for lighting apparatus which is low-cost and energy efficient. LEDs (light-emitting diodes) provide light sources which are energy efficient, and advances in LED technology are providing even greater such efficiencies over time. In addition, one advantage of using LEDs as light sources is simply that the smaller packages of such sources translate into much lower material usage within fixtures containing such sources, thus yielding the attendant cost-efficiency. As the technology advances and the cost of LED packages is reduced, such material usage cost benefits will become more important.
Typical applications for lighting systems are roadway and parking lot lighting in which there are performance requirements that light be as uniformly distributed over areas which are to be lighted while the neighboring regions should be free of light spillage. Thus, along roadways and in parking lots, there is a need to be able to direct light in a laterally-biased direction to avoid so-called trespass lighting on neighboring houses, for example, while providing uniform lighting to the roadways or parking lots.
Various LED packages have lenses, some including secondary lenses, for various purposes not related to preferential lateral directing of light. In addition, some limited efforts have been made to develop light-directing LED apparatus using small lenses over small LED light emitter packages, and utilizing lenses intended to redirect some amount of emitted light to one side preferentially. However, such lenses, utilizing lens surfaces having one or more projecting elements and extensive regions of discontinuity, fall well short of requirements to avoid trespass lighting. The measure of trespass lighting includes more than just the amount of light energy falling toward the non-preferential side but also includes how far into the area on the non-preferential that the light falls.
The requirements for avoiding trespass lighting may even indicate in some applications that it is preferable to absorb light rather than to allow it to be emitted into the area on the non-preferential side.