IEC/EN 61000-3-3

Harmonics are “non-linear” Currents or Voltages in an electrical distribution system, caused by non-linear loads (i.e. loads that draw current with a waveform that is not the same as that of the supply voltage).
Typical devices that cause harmonics are motor driven equipment, domestic appliances (TVs, microwave ovens, lighting equipment and dimmers), and office equipment (PCs, printers).

The IEC standards that deal with Harmonics are IEC 61000-3-2 for products <16 A/phase, and IEC 61000-3-12 for products <75 A/phase.
Typical equipment for Harmonics measurement should include a pure AC power source, and a Harmonics analyzing system.
Flicker is caused by rapid power supply voltage fluctuations, which results in light luminance fluctuation. Limiting flicker is achieved by limiting the voltage variations generated across a reference load.
The IEC standards that deal with flicker are IEC 61000-3-3 and IEC 61000-3-11.
The basic instrumentation used to measure flicker has the same characteristics as the harmonics analyzer, and therefore the same type of test equipment is used. However, what needs to be added to the configuration is a reference impedance, or Flicker impedance, in order to simulate the resistance and inductance of the low voltage distribution systems. Another main difference is in the measurement, as the voltage across the point of supply is measured, rather than the current drawn by it.