LIGHT – what is it?
How light is produced and why we see it
GENERAL INFORMATION ABOUT LIGHT
Light is life – it surrounds us, always and everywhere!
We orient ourselves by the day-night cycle, the seasons and, of course, the artificial lighting in our surroundings. Without the invention of artificial light, we would probably be at a complete loss in today’s world. Thank goodness for Edison!
WHERE DOES LIGHT COME FROM?
To understand light and artificial lighting, we first need to look at how it is produced and how it works.
Light is produced through energy conversion. In the sun, for example, our largest natural source of light, hydrogen atoms fuse to form helium, emitting light and heat in the process. In a conventional incandescent bulb, the filament is made to glow by the flow of electricity; here too, heat and light are produced. In LED lighting, light emission is based on the principle of electroluminescence from a semiconductor crystal.
LIGHT IN PHYSICAL TERMS – QUITE SIMPLY
It is both a wave and a particle. Its properties always consist of both. Reflection and refraction can be explained by both waves and particles, but diffraction and polarisation only by particles. This is very complex, and we are no Einsteins – after all, he did win the Nobel Prize for the discovery of the photoelectric effect. For us, the only thing that matters is this: for artificial lighting, we need the wave properties of light.
VISIBLE LIGHT – THE LIGHT SPECTRUM
The part of the light spectrum visible to us ranges from approximately 400 to 700 nanometres, so it is relatively limited! Below 400 nm, i.e. in the short-wave range, lies ultraviolet radiation up to X-rays. In the long-wave range above 700 nm, we refer to infrared light and microwave radiation.
WHAT WE PERCEIVE
Light passes through our pupil onto the retina at the back of the eye. There are receptors there that capture it: the so-called rods and cones. The rods are responsible for light-dark contrasts, the cones for color vision. We have about twice as many rods as cones. As soon as light hits these cells, biochemical reactions take place and electrical impulses are transmitted to the brain via the optic nerve. The cones only function well in sufficient light – after all, there are far fewer of them! That is why we see fewer colors in the dark and at twilight.
So the saying ‘All cats are grey at night’ is no coincidence.
The human eye is best suited to the mid-range wavelength of around 550 nm; the cones responsible for green perception are clearly in the majority. That is why we also perceive the color ‘green’ as soothing and pleasant; we do not have to strain to take it in and process it. After all, it occurs most frequently in nature in all its mixtures and shades.
Source: www.licht.de
PROCESSING IN THE BRAIN
Once all the information has reached the brain via the optic nerve, the real work begins. Brightness and colors are interpreted and evaluated. If necessary, they are also adjusted and ‘enhanced’. The older we get, the less effectively these processes function, meaning we need more artificial lighting. At the workplace, for example, or when reading. This is why the EU Workplace Directive also makes an effort to specify appropriate illuminance levels for various activities. These levels are comfortable for the respective task and designed to support the work. A surgeon needs completely different lighting to a baker, or indeed a shop assistant. The International Commission on Illumination in Vienna also conducts research on this and issues recommendations and guidelines. The influence of our perception of colors and light on our well-being and even on everyday decisions cannot be dismissed, and above all should not be underestimated.