The other principle, the reflective LV, works by either reflecting the light towards the target or deflecting it away. The portion of light that is reflected on the target decides the gray scale. This re- and deflection occurs many times a second. Should this happen at too low a frequency, the human eye and brain would perceive it as flickering, but due to sufficiently high frequency, a human will be "tricked" into viewing it as a continuum, a smooth shift in brightness. Examples of the reflective LV type are the digital micromirror device (DMD), Eidophor 's oil-film based system, and the grating light valve.