Discuss your entity or other experiments here. I'll start!
I've been experimenting with some Lightning effects in Source and initially I had a lot of light entities, brightness 3000, scattered around this room. These were triggered by a relay which also triggers some sound files (selected randomly, logic_case) and fires a small env_shake. Now when I test-fired this relay, there's a bright white flash. Obviously, right? But there are a few areas that don't get light and as such remain pitch black - There's a huge white flash encompassing the room and two surfaces remain pitch black as they normally are when the room is not in lightning state (for .4 of a second.)
Additionally, the room pretty much turns fullbright and as a result of this state some things get buggy - Notably some culling effects on transparency (railings) and the game lags for abit. This is just like being in a mat_fullbright state.
As a result I toned down the lighting (the regular ambience in here is ~75 anyway so some 600 brightness lights will do. Outdoors it can be brighter but we're inside anyway.) Also, I filled in the darker areas that werent being lit with some more point lights. I surmise that the reason these did not get lit is that they're initally dark and the initally dark lights don't get a proper lighting calc for surfaces, as the regular pass does.
Post some of your recent or interesting Source experiements, their issues, solutions (if you fixed it) or leave it open to discussion and answer by others if you can't figure it out yourself!