Binary holograms have become more interesting since spatial light modulators, capable of binary phase modulation, were developed. The primary restriction of these dynamic elements when used with the Fourier transform is the symmetry of the hologram reconstruction. I describe a new type of hologram that uses the Hartley transform instead of the Fourier transform. Despite their binary form, Hartley holograms offer maximal efficiency (theoretically 100%). Thus they can be presented as high diffraction-efficiency programmable elements. For practical reasons, I also propose a modified version for Hartley holograms that is easy to use. A theoretical analysis as well as experimental results are given.