It can signify anything and nothing, this found pop object; Johns called it a “thing the mind already knows.” Your kids understand it, and probably your dog, too. It’s either on or off but never in between. It’s in a state of being, not becoming. So long as there’s current, it simply exists. And in opposition, there’s just darkness.Artistic obsessions can run too far (see: Henry Darger, children) or just far enough (Monet, water lilies). The Light Bulb series by Jasper Johns belongs to the second camp. He began sketching bulbs in the late ’50s, then created multiple versions in sculpture, crayon, and paint for the next 20 years. As in his famous Target series, there’s something about the simple, utilitarian shape that invites iteration. The bulb, socket threads, switch, and cord are so unadorned, so neutral in their meaning. The humble glowing orb suggests the genius of Thomas Edison and the cartoons of George Booth.Henry Art Gallery, 4100 15th Ave. N.E. (UW Campus), 543-2280, henryart.org. $6-$10. Sat.-Sun., 11 a.m.-4 p.m.; Thurs.-Fri., 11 a.m.-9 p.m. Through Oct. 25.