Reel to Reel Institute’s logo is a model of carbon arc lamp, light source of the earliest film projectors, which had been used until the late 1960s. In a carbon arc lamp, the electrodes are carbon rods in free air. To ignite the lamp, the rods are touched together, thus allowing a relatively low voltage to strike the arc. The rods are then slowly drawn apart, and electric current heats and maintains an arc across the gap. The tips of the carbon rods are heated and the carbon vaporises. The carbon vapour in the arc is highly luminous, which is what produces the bright light. The rods are slowly burnt away in use, and the distance between them needs to be regularly adjusted in order to maintain the arc. The length of those carbons was about 20 minutes which also dictated the length of the reel. Prior to the 1960s, projectionists used a ‘change over system’. The carbons and film reels in one machine would be refreshed while the other machine was running. It is also the meaning behind ‘Reel to Reel’, in the notion of impetus, preservation and inheritance.