LightUp is described as 'allows placing light sources (including IES) inside your SketchUp model and navigating the lit results in realtime. You can add reflections, panoramas, skybox and generate high resolution Movies and Still images all from inside the SketchUp window' and is an app. There are four alternatives to LightUp for Sketchup, Windows, Mac and Online / Web-based. The best alternative is Clara.io, which is free. Other great apps like LightUp are Twilight Render, SU Podium and IRender nXt.