A channel letter lighting unit according to the present invention comprises a printed circuit board having a plurality of linearly mounted light emitting elements. The yoke has a zero yoke angle and a plurality of non-zero yoke angles. The lens is disposed with respect to the digital image sensing unit such that the optical axis extends through the part of the first legally-prescribed field of view that is reproduced on the digital image sensing unit. In this manner, lock of the downstream signal to the reference clock signal may be accurately assessed in one embodiment. Positioning mechanism comprises three degrees of freedom of motion for establishing the spatial relationship of adapter to clamp assembly, two of which are in the horizontal plane.