"One factor in valuing a Flavin, however, dwarfs all others: the certificate that accompanied its production. To those who wonder what the difference is between a Flavin and the lights in their office, the certificate, more or less, is the answer.

Each of the more than 750 light sculptures that Flavin designed - usually in editions of three or five - were listed on index cards and filed away. When one sold, the buyer received a certificate containing a diagram of the work, its title and the artist's signature and stamp. If someone showed up with a certificate and a damaged fixture, Flavin would replace it. But without a certificate, the owner was out of luck. Today, Christie's won't even consider a Flavin sculpture unless it's accompanied by an original document."