It first appeared on Halloween: a concrete parking lot dressed up as an unkempt grassy field twinkling and flashing under the moon. Taking part.

Then, on the night of November 9, it reappeared in another form (the original, intended form—the manufacturers made a mistake and provided rods the wrong lengths at first): a grid about 65 by 110 feet with fluorescent rods cut to various heights (from 2 1/2 to 8 feet tall) and arranged specifically to form multiple, giant sine waves. It's called Oscillating Field and it's by Dan Corson. (He also has an installation at Suyama Space.)

Walking by it now, especially at night, is an exercise in not knowing what you're seeing, which is a brain treat. Here are the common questions: How are the rods stuck in the concrete? (They're just set there, in tiny holes made by a roto-hammer.) Are the rods electrical? (No, they're just yellow-orange fluorescent fiberglass rods with tops painted with construction orange paint.) So where is light coming from? (Two green lasers at two corners of the grid.) How's it powered? (A computer plugged into a generator tells the lasers what to do; City Light for unknown reasons wouldn't let the artist plug into the Christmas lighting poles.) What's the choreography? (Nine patterns that run in a 32-minute loop.)

Even when you know all the answers, your eyes cannot pin down what's going on when you're out there. First of all, the light is continuously moving. Second, you're walking. And any place you stop, you have only one vantage point. Your brain wants to know things: I see this here, but how does it look from over there? Your brain wants solid form but this is an environment built on gaps in space and time, full of air, never adding up to a solid form. Plus, you're looking at it through the curls and lines of a chainlink fence, and even if you don't know for sure, you have to assume that something this fragile is temporary. (Oscillating Field will, in fact, only be up until construction starts on the Capitol Hill light rail station after the first of the year.)

There are plenty of ways to read it as imitation. When the lasers move vertically, the rods look like reeds growing in time-lapse. Or like illuminated rain coming down. Clumps of rods isolated from the grid look like patches of weeds. That's nice. But I like the simple fact that it stays in transit.