The 49-strong column of light is visible from far across town, even way out into the suburbs, shooting up into the sky (and probably hitting the clouds, which makes for a mysterious Bat Signal-like effect).
It was ridiculously busy alongside the Palace of Westminster last night, with hundreds of Londoners filing expectantly towards Victoria Embankment Gardens (but thankfully there were no queues).
You could spot the foreign tourists in Parliament Square last night, they were the folk still pointing their cameras towards Big Ben rather than the temporary blue column of light erupting from behind the Victoria Tower.
To enter the square platform and hear the sinewave soundtrack, climb the ramped edge and step inside the 7×7 grid of mega-powerful spotlights (it gets more dense with people the closer to the centre you go).
5) Look up
From anywhere within the grid the beams look very different to outside, not a magnified single beam but severalthreads rising like a maypole to a crown of light diffusing into the clouds.
Stand right beside one of the spotlights and you can easily peer into it should the fancy take you, to see a clean bright white light erupting from within (but that's your night vision buggered).
A number of visitors seem to think it's a good idea to sit down on the floor within the grid of lights and stare upwards (and no doubt it is, until someone whose night vision is buggered trips over them).
A better place to hit the floor is outside the grid within the main body of the Gardens, where reclining Spectra-worshippers form a ring around the electric henge (some have even brought a picnic).
No modern art event is possible without the taking of countless digital images and their dispersal via social media. Nigh everybody has a phone out (usually for a beam shot, but sometimes for a Spectra selfie).
If you thought this was a special one-off commission to commemorate WW1 you'd be wrong - Ryoji Ikeda's lightwork has already adorned the skies in Paris, Barcelona, Buenos Aires, Hobart, the UAE, etc.
A lady from Artangel is standing by the entrance to Victoria Embankment Gardens counting every visitor with a click. She's going to be damned pleased with her total by the end of the weekend.
12) Hurry Spectra is a seven-day event, firing up from dusk to dawn for seven nights only. And last night was number six, so you only have tonight to get down and experience the column of white light at close hand.