Many existing indoor localization systems have achieved applaud-able performance through comprehensive modeling of its envisioned working scenario. However their real life deployment are often prohibited by high deployment overhead and performance degradation in dynamic environments. This paper presents SmartLight, a 3D digital indoor localization system based on LED lighting infrastructures. It adopts a novel design philosophy of shifting all the complexity into modifying a single LED lamp and maintaining minimum complexity on the receiver to reduce the hassle on system deployment/calibration. With a single modified LED lamp, the system is capable of localizing a large number of light sensors in a room. The underlying technique is to exploit the light splitting properties of convex lens to create an one-to-one mapping between a location and the set of orthogonal digital light signals receivable at that location. Advanced designs are also introduced to further improve the system accuracy and scalability beyond the hardware capability. In evaluating the design, we build an experimental prototype with a 60hz projector, achieving average localization around 10cm and 90 percentile error of 50cm.