The Lumped Element Kinetic Inductance Detector (LEKID) is a single layer superconducting detector which provides a simple and elegant solution for producing large format, multiplexed arrays of background limited detectors for ground based astronomy. The LEKID design incorporates both the detecting element and absorber of an array pixel which does not require feed-horns or antennas to couple in light from a telescope. In order to achieve good optical efficiency across an atmospheric window, the geometry and material choice of the LEKID need to suit the observing band of interest. In addition to this, the geometric and frequency spacing of LEKIDs in an array needs to be optimised to limit crosstalk between pixels and make full use of the bandwidth of the multiplexed readout electronics. In this paper we discuss each of these design aspects of the LEKID and present results for LEKID pixels designed to work at 200 um and 2mm.