Light and its phenomena

Light and its phenomena
Human vision

Light and its phenomena

Technically speaking, light can be defined as the field of electromagnetic radiation ranging between a wavelength of 380 nm and 780 nm, which reaches our brain through our visual system, enabling us to see the world around us.
Each wavelength in the field of visual radiation is perceived as a certain colour in a spectrum from violet (about 400 nm) to blue (450 nm), to green (500 nm), to orange (600 nm), to red (700 nm).
The human eye does not always respond in the same way to the individual colours in the light spectrum, nor to different illuminations. In daylight (photopic vision) it is most sensitive to radiation in the middle of the spectrum (yellow-green colour - 555 nm), while sensitivity gradually decreases and is eventually cancelled at the ends of the spectrum.
In dimmed light (scotopic vision), for instance at night, the sensitivity curve shifts by 48 nm towards violet.
As a consequence, at the same energy radiation level, a room will appear brighter if it is illuminated with a yellow light, whereas soft cold colours (blue and violet) will be better perceived than warm ones (orange and red) in dim light.
A perfect perception of colours and small details requires strong illumination. This may be achieved with light sources with a compact light spectrum, inclusive of all the visible wavelengths.

The light required for appropriate visual perception varies with age, and is not identical for all individuals. From birth throughout growth, human beings need 4 to 5 times more light than adults; this requirement recurs at an advanced age, above 50. It should be noted, however, that each individual is different. All environmental stimuli are important to visual perception; they influence vision, and thus taste in light. Such factors as the latitude at which one is born, race, and culture, as well as primeval and ingrained habits, affect us.
In the same way as we may prefer a dress, a colour, or a music according to our birth place and our culture, thus we may deem a certain light, its colour, intensity, and effects particularly pleasant.
Note that light radiation is not only transformed into visual sensations by the brain; a part of it also affects the centre controlling an individual’s psychophysical state, mood, ability to pay attention and concentrate, and behaviour; indeed, inappropriate illumination can be a source of discomfort, and even of stress.

The purpose of this manual is to provide the basic knowledge required to stimulate the reader's imagination and creativity in using artificial illumination, not just to identify the best suited evening or night illumination in the individual rooms of the home, but also to create ambiances reflecting the taste and personality of their inhabitants.
Our main focus, when venturing on the difficult task of giving a home the best possible illumination, is on the effects perceived by the eyes and the visitors. Light passes through, or is reflected by surfaces and objects in the interior of our home, and enables us to see and enjoy the beauty of the people, the furniture, and everything else around us.
Any atmosphere is the result of illumination, and any interior changes its appearance, and affects us differently, as lighting changes.
The world around us is only perceptible because it is lit, perhaps half in shade, but nevertheless illuminated. A total absence of light is profound darkness, lack of visual sensations, an immaterial world, nothingness.

The human vision

The human vision
Due to the important role of the vision of our environment in our life, our visual apparatus has developed in such a way as to function in the broadest variety of lighting conditions. Our eyes can adjust to the burning sun of the desert and the thousand reflections of a mountain glacier, as well as to the half-shade of a forest or to the full moon at night. Our world is made to be lit at all times - by the sun in the day and by the stars and moon at night.
Therefore our visual apparatus, formed by the eyes, the optical nerves, and the visual cortex of the brain, functions uninterruptedly, including while we dream.