[this Ryoji Ikeda piece] was laid on specially for La Nuit Blanche [edit: not sure if it's reused elements of his spectra [amsterdam] piece]. It consisted of a 8 x 8 grid of, um, spotlights pointing upwards into the sky, aimed at a spot roughly 2x the height of the Tour Montparnasse, plus a music that was around 30 minutes long that looped (yes, I braved the cold for an hour to mke sure). Absolutely beautiful stuff. It was designed to have a sort of low base tone with another that modulated based on head positioning and that would not resolve/sync at all (difficult listening!). Then, every 12 seconds, a short sonar-esque note an octave or two higher, with occasional super high Ikeda brand barely audible aural flutter and static that occasionally went percussive (faintly, briefly). Then, every 24 minutes or so, a 6 minute section of extremely low bass pulses that slowed down and back up over time (think inverted parabola) that physically chopped up anything else you were hearing (eg the public making a lot of noise). The second time it kicked in I hugged one of the 64 boxes (with spotlights and hidden subwoofers) and watched the sky - it was an incredible physical sensation.
Sadly the crowd was largely indifferent to the audio, preferring instead to try to play with the (huge, hot) spotlights or talk loudly with friends. It may have been better with concert level quiet, but that was definitely not going to happen.
Walking away from it, the secondary base tone fell away due to acoustical mathemathics leaving only the base tone that (I'm guessing) was more closely in alignment with Western tuning, which lead to a sort of jouissance or whatever, a sense of resolution and peace and calm. I did in fact tear up once we'd reached that point.
I'd give it a 10 out of 10 in terms of an Overall Artistic Experience. Way cool.
[edit: More information here: http://www.forma.org.uk/programme/public-realm-projects/spectra-paris]