Can interfere with light of different wavelengths

What is light

What is light - basic principles for your art

Light surrounds us all the time. To a large extent, it is what makes life possible in the first place.
We and our whole culture are fixated on it. It structures our life by alternating day and night. Gives us orientation and lets us recognize colors.
With the invention of artificial light sources, we have also made the night and interior usable. Whether in the living area and - especially - at work, without artificial lighting we would have to live with severe restrictions.

Light - whether artificial or natural - is a crucial component and also a factor in the practice of art. Understanding light is extremely important when creating art - whether for furnishing your studio, illuminating exhibitions or creating works of art directly.

In order to better plan and understand lighting, it is helpful to understand how light works.
In the following we have condensed the difficult topic and hope to reproduce the essential aspects.

How is light created

Light is created by converting energy. In our largest source of light, the sun, e.g. by fusing hydrogen atoms to form helium. Heat and light are emitted, both of which hit the earth and significantly shape our planet.
In artificial light sources, e.g. an incandescent lamp, a metal wire is made to glow - here, too, heat and light are given off to the environment. The LED is based on the principle of electroluminescence from a semiconductor crystal. Here, too, heat is generated (albeit to a lesser extent) and light.

The physics of light

Light is both wave and particle (wave-particle dualism)
Some properties of light can be explained as particles, others as waves, and still others with both.
Reflection and refraction can be explained as waves or particles. Interference, diffraction and polarization can only be explained with the wave properties of light.
The photoelectric effect, however, can only be explained by the particle properties of light. Here light with a (and only one) minimum energy knocks electrons out of a solid. If you increase the amount of light, more electrons are knocked out of the body. However, this does not increase the speed of the electrons - this requires light with higher energy (towards ultraviolet). This is called wave-particle dualism and it is based on Heisenberg's uncertainty principle. The position or momentum of a particle cannot be determined exactly together. E.g. if the location is determined exactly, the intensity of the impulse cannot be measured. (Further information can be found e.g. at Wikipedia)

What is important for us in lighting is the wave properties of light.
The optical light - which is decisive for lighting technology - is in the range from 700nm to 400nm. The microwave radiation and the infrared radiation lie in front of the 700nm. After the 400nm are ultraviolet radiation and X-rays.
nm stands for nanometer - the unit of the oscillation of the light wave in billionths of a meter (measured from the wave crest to the next wave crest)
The energy of the light wave decreases with increasing wavelength. That means, red light with 700nm is lower in energy than blue / violet light with 400nm.

Propagation of light

Light spreads evenly from the light source. The speed in a vacuum is c = 299,792,458 m / sec. (Speed ​​of Light)
If it hits a body, for example, its spread can be disturbed.

absorption

If light hits a black surface, for example, it can be partially or completely "swallowed" or absorbed. The absorbed radiation is converted into heat.

Reflection and body colors

If the light hits a body, it is reflected back (except for the part that is absorbed).
The angle of incidence and the angle of reflection are always the same. For lighting, among other things, it is interesting that certain wavelengths of light are absorbed by bodies and others are reflected. This creates the colors of the objects. If, for example, light in the red wavelength range is reflected back from a body surface, the body appears red. Man is talking about body colors here. We can then only perceive the red, reflected wavelengths.

It is also important for the lighting that (logically) only wavelengths can be reflected that were previously present in the spectrum of the light. This can disrupt the natural color rendering of the surfaces. If there is no red-wave light in the emitted light, the illuminated body can of course not appear red - the body appears dark. In lighting technology, one tries to reproduce this with the Color Rendering Index (CRI) or Ra. Luminaires with a high CRI (> 80) are suitable for office applications. For work areas, the CRI is specified in the Workplace Directive.

refraction

If light hits a transparent body, it is more or less refracted. This means that the entry angle is changed depending on the refractive index of the material. This effect can be observed very well with glass and especially with frosted glass.

Dispersion

A subtype of refraction in which, for example, light is broken down into its wavelengths in a prism. The different spectral colors of the light become visible.

interference

Play of light like on soap bubbles or a layer of oil on water is created by different refraction of light in wafer-thin surfaces.

Light in lighting technology

Knowledge of the behavior of light helps us to use artificial light better. Light from the LED has a relatively narrow band and is rich in energy (blue LEDs).

Broadband light or light of a different color is generated by means of a phosphor layer on the LED. Optics above the LED direct the light. The broader the light, the better the color rendering.
In the room to be illuminated, light hits the walls, floors and furnishings. It is reflected and absorbed there. This changes the lighting significantly. Daylight is refracted in the glass and reflected in the room and can thus illuminate considerable parts of the room.

Perception of light (day and night vision)

Light is absorbed by the human eye. Like a camera shutter, the pupil lets more or less light onto the retina.

If the illuminance in the room is high, the pupil lets in little light and is fully open at night. On the retina, uvula are responsible for color perception and rods for the light-dark contrasts. The suppositories only work well when there is sufficient lighting - the reason why we hardly perceive any colors at dusk.

Suppositories work best at 555nm. Colors are clearly perceived here (photopic vision). With decreasing lighting, the function of the uvula also decreases.
In twilight or at night, the rods do most of the work (scotopic vision). These work best at a wavelength of 507nm.
In the meantime (twilight) one speaks of mesopic vision.

All information is passed through the optic nerve to the brain where the information is interpreted. Low illuminance levels can also be compensated here - but this is exhausting in the long run. With increasing age, the eye can no longer adjust to different illuminance levels as quickly. You need more light for activities that were easy to accomplish when you were young and in poor lighting conditions.
The Workplace Directive attempts to specify illuminance levels for various activities that are comfortable for most people for the respective activity and that provide the best possible support for their work.