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'. 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 (Paid), SU Podium (Paid) and IRender nXt (Paid).
Clara.io is a full-featured cloud-based 3D modeling, animation and rendering software tool that runs in your web browser. With Clara.io you can make complex 3D models, create beautiful photorealistic renderings, and share them without installing any software programs.