The initial phase with which the source emits waves can change over time in an unpredictable way.

The wall-mounted light sources emitted only a dim illumination.

Stationary sources emit greenhouse gases from a single point source such as a smoke stack.

But as that source can emit harmful levels of radiation, extra precautions are required.

Many sources emit radiation that is well below natural background levels.

Conventional light sources emit waves of differing frequencies and at different times from different points in the source.

A light source - say a candle - emits light in all directions.

This is because all light is in a mode, and most light sources emit into many different modes.

The light source usually emits the full spectrum of light.

Two sources, side by side, emit water into the uniform flow in a water channel.