The light wavelength and its temperature

Light is the part of the electromagnetic spectrum visible to the human eye. It is an electromagnetic wave and has its wavelength, or frequency, between 400 and 700 nanometers, inside which all the colours we can perceive are contained. In addition to visual perception, the colour of the light can also indicate what is the temperature of a light source, like an infrared lamp.


Perceivable colours and infrared

The colours of the light that our eye can perceive range from red to violet. Exceeding these wavelengths, we talk about infrared radiation for those with longer wavelengths or ultraviolet for those with shorter wavelengths.

The colour-wavelength relationship, however, is not two-way. In fact, if for every wavelength we can associate a colour, the opposite is not valid. So, it is not true that each colour corresponds to a precise wavelength.

This happens because the colours that we see are not just a physical phenomenon but are also created by our brain, which processes the information received from the eyes. To complicate matters, most of the light radiation that we can see is due to a mixture of radiation with different wavelengths; therefore, colours we see are the sum of other colours.

Being outside the visual spectrum, man can’t see infrared frequencies, but he can still perceive them. In fact, the infrared wavelengths of the electromagnetic spectrum can be easily perceived as heat from our body.

It should be added that almost all the wavelengths of the electromagnetic spectrum can be perceived as heat; for example, the so-called ultraviolet rays are responsible for sunburn. However, their perception is different and much less intense than the infrared frequencies: often we notice their effect only when the skin is already burned.


The light colour temperature

The bond between light and heat therefore is indissoluble, so that one can have an idea of ​​the temperature of a light source basing on its colour. In detail: the colour temperature of a light radiation is the temperature that can be associated with a light source like the radiation in question.

This is possible thanks to the correspondence between colours and wavelengths. Therefore, to red, orange and yellow shades will correspond the lowest temperatures, while for lights that approach white, blue and purple colour the correspondence is at higher temperatures.

This means that, contrary to what one may think, the warm light tones are colder than those traditionally we associate with cold colours. In fact, while to the red light of the fire, longer wavelength, corresponds a temperature of about 1500 ° C, the colour temperature of a blue-white light, source with a shorter wavelength, is about 5 times greater: 7700 ° C.


Colour temperature and infrared lamps

Let’s summarize: light, heat and colour are inextricably linked because they are 3 expressions of a single phenomenon: electromagnetic radiation. The light is practically “composed” by the visible colours, it is in fact the portion of the electromagnetic spectrum that we can see.

To a certain type of light corresponds a temperature, higher temperatures for cold lights (white, blue or purple), lower temperatures for warm lights (yellow, red and orange). Infrared radiations, although invisible to us, are easily perceived as heat.

All this put together can make us understand why we use infrared lamps to heat the environments. First, the colour temperature of an infrared lamp, even if it is of the order of a thousand degrees, is lower than that of white or coloured halogen lamps. This means that it is very difficult for an infrared lamp to “burn” us.

An infrared lamp is suitable to heating an environment also since infrared rays are the electromagnetic radiation most easily perceived by substance, by human body, as heat thanks to their wavelength.

We conclude by making an example: infrared cameras transform the heat emitted by a body into a visible image; diametrically opposed, it can almost be said that infrared lamps transform visible light into a heat which is pleasant and not harmful for human organism. This is because the radiation emitted by an infrared lamp is the most effective way in nature to transmit and make the heat feel.

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