Four TetIt’s a problem a lot of music festivals seem to have around here: It’s 11:30 p.m., the mainstage headliners just shot their last cannonfuls of confetti and finished their second encore, the food carts have packed it in, and all of a sudden there’s nothing to do. If you’re out at the Gorge, you might go back to the campgrounds and look for a Canadian-flagged bus equipped with a sound system; if you’re at a festival inside city limits, you might hop in a cab and hit up any number of unofficial after-parties. These ad-hoc, atomized solutions are fine, but why shouldn’t the festival itself get in on the late-night action? That’s exactly what Bumbershoot aims to do this year, in cooperation with Decibel Festival, by hosting Bumbershoot After Dark, a separately ticketed party in the Seattle Center Exhibition Hall that will run from 11 p.m. to 4 a.m. on Saturday and Sunday nights featuring some seriously top-ranking electronic artists and DJs. Saturday night brings SF tech house dirtybird Claud VonStroke, Miami’s DJ Craze, and Toronto’s Jokers of the Scene for what should be an all-out raver. On Sunday, while Wiz Khalifa’s fans–and pot smoke–are still dissipating, L.A. synth-boogie wizard Dam-Funk will just be getting things warmed up for a show that also includes thoughtful yet blissful British beatmaker Four Tet and a yet-unannounced Low End Theorist whose glitchy jazz and hip-hop instrumentals should keep spirits Flying.The events, along with the Decibel-curated EMP Skychurch stage in the festival proper, will also serve as some fine last-minute advertisements for the electronic-oriented Decibel Festival, which follows close on the heels of Bumbershoot, over the long weekend of September 28-October 2.The sticking point here for many festivalgoers will be the idea, as well as the real-world cost, of an additional ticket. But for anyone familiar with the overhead involved in running a more or less all-ages event (16+), with alcohol (for the 21+ crowd), that runs two hours after last-call shuts down revenue-generating liquor sales–well, let’s put it this way: $22 (adv/$30 at the door) wouldn’t be that much more than you’d pay to see Four Tet and Dam-Funk under far less financially prohibitive circumstances. All in all, this is a smart move for Bumbershoot, a festival which has in recent years perhaps started to look a little stodgy and tame compared to hipper, younger festivals like Sasquatch and Capitol Hill Block Party. This year, hours after the parents have gone home with their double-wide strollers, the party will keep on raging. Nice one. Tickets are available at http://bookr.net/BumbershootAfterDarkSaturday and http://bookr.net/BumbershootAfterDarkSunday.Follow us on Facebook and Twitter.