[5.9.9.7] As pertaining to temporal light modulation: For a rectangular wave, the ratio length of time over a single cycle that the light modulation waveform is at a high magnitude state, as a percentage of the total cycle time. The low state can be a low value or 0.
Note: This is defined differently than in the electronics world, where the duty cycle is the percentage of
time a device operates in the ON state, while the rest of the cycle is operating in the OFF state.