Lightup is another 3rd party rendering extension available for Sketchup, but one with a difference. Unlike all of the others, the Lightup extension allows you to render your 3d model and then walk around the rendered environment in realtime - all within Sketchup. It is truly amazing!
Author Adam Billyard has a long history in the computer gaming industry and he has packed his realtime 3d rendering know-how into this extension. Using a fairly basic interface that works with Sketchup’s main model window, you simply place your lights, define your materials, set the background environment and press go. Well it is a bit more complicated than that and there are many different settings, but in essence it is easy to use, fast to render, and the results are very surprising.
And there are also various accompanying cross-platform viewers which can be used to view the rendered 3d models including a standalone iPad/iPhone player, as well as web players that work with the most common browsers. I did have embedded into this webpage, an example of a virtual art gallery that I created and it was working until recently, but unfortunately recent changes to internet browser security means that the web player plugin no longer works. Hopefully the author will address this issue in the near future.
EDIT 5/1/17: It does appear that internet browser security is moving away from plugins and moving towards HTML5 for embedding interactive media. It may mean that an HTML5 based solution may end up replacing these web player plugins.
Apart from the many architecture/building design possibilities, Lightup has many other applications particularly as it can export light “baked” textured models to FBX format, a common file format that can be imported by many other programs, most notably the Unity gaming engine. Lightup also boasts a bit of a following at Pixar (animated film company).
In terms of rendering quality, output is not quite up there with traditional raytrace renderers and I guess that is the trade-off of being able to walk around in a realtime 3d environment, so it is really about what your particular needs or preferences are. It is not the cheapest plugin either but very few good things are free in this world. Definitely worth a look if you do a lot of interiors and want to give your clients an interactive experience.
You can download the standalone Lightup players from HERE and download the art gallery .luca file from the link at the top of the page (where it says Download attachments: Linda's Gallery .luca file under the title of the article) which you can view with the player.