The term radiation refers not only to a mechanism of heat flow, but a type of energy, electromagnetic radiation . There are other important types as well. Thus, ultraviolet light is more energetic. This is why it can cause sunburn, but an ordinary lightbulb does not. We can see only a tiny fraction of the light in the EM spectrum, but we can build instruments to detect colors in the entire range.
Water vapor is water in a gaseous state.
Water can be transformed among these states of matter by such familiar processes as freezing, melting, evaporation, or condensation. Humidity is the amount of water vapor in the air. The maximum amount of water vapor that air can hold depends on the temperature. The higher the air temperature, the more water vapor that it can contain. When air contains all the water vapor that it can hold, it is saturated .