Jasper Johns asked Billy Klüver for a transparent gas-discharge letter to include in a painting. He wanted the power supply to be mounted behind the painting without any power cords attaching the painting to the wall. To do this a high voltage supply was needed, but  to stack up batteries to 1200 volts would have been messy, dangerous and impractical. Klüver's colleague at Bell Labs, Harold Hodges, solved this by the ingenious idea of  building a multi-vibrator circuit which converted the DC voltage from a 12 volt rechargable battery into AC. Transformed into 1200 Volts and then rectified, it powered the neon letter. All the technical equipment was mounted behind the painting.  Using this device they were able to provide  the blue “A” which sticks out horizontally at the top of the painting in Zone, 1962. The letter  "A" was to be blue, and could be obtained using mercury so the letter would be transparent when the letter was turned off.  With any other color, one would have to use fluorescent material on the inside of the glass tube to produce color, which would look white and opaque when the voltage was turned off.  Johns wanted the letter to be transparent. Klüver then found a neon sign maker in Newark, who could make the "A" to his specifications.

​

Johns  later asked Klüver for a red "R" for Field Painting, 1964. The glass  "R" was filled with neon which naturally became red when turned on.