La lumière naturelle

Gabriel Dupras, Vice president of Research and Development
Contenu disponible en anglais seulement.


Daylight distinguishes itself by its daily and seasonal nuances, in which nature moves cyclically from sunrise to sunset. Sunlight’s varied gamut of transformations majestically imposes its cadence to terrestrial activity. Inspired by the synergy between living beings and natural light, Sollum Technologies created the only lighting solution that can recreate and modulate the full spectrum of natural light in all of its complexity.


The expressions “sunlight” and “daylight” are often used interchangeably. We’ve elected to use “natural light” in this document because it unifies and specifies the nuances of sunlight as it is transmitted to Earth during daytime.

Light emitted by the Sun is electromagnetic radiation. In effect, it is a kind of evacuation of excess energy transported by a ray of light. Sunlight covers a large spectrum referred to as the electromagnetic spectrum, of which only a segment is visible. The visible spectrum can be represented by a graph similar to the one presenting the Sun’s signature above.

Only a small fraction of the light the Sun emits is directed towards Earth. In the course of its motion, a sun ray is fundamentally altered by its interactions with the matter that comprises the Earth’s atmosphere. When measured in space, the Sun’s spectrum is different from the one perceived on the Earth’s surface. Indeed, different parts of the Sun’s light spectrum are reflected, absorbed, diffused or refracted in various ways by the particles, dust, water vapor, clouds and other gases that make up the atmosphere.

Solar spectrum outside the atmosphere (in black) and on the ground at 37° south (in red). [ASTM International, 2005]

The figure compares the electromagnetic radiation observed outside of the atmosphere with oneobserved within the atmosphere (in which life evolved).

The Rainbow

To better flesh out the advantages of representing light by its electromagnetic spectrum, the example of the rainbow is a useful device because it vividly demonstrates how natural light is composed of an amalgamation of different colors. The rainbow is one of the few natural manifestations of the dispersion of white light. In effect, water droplets suspended by humid weather refract the colors that comprise light in the same way a prism does.

The human eye only perceives a unified white color, but natural light is composed of a diversity of colors in distinct proportions. One observes and measures light with a spectrometer. The device represents light as a subtly segmented range of wavelengths measured in nanometers (nm). The visible range goes from 400 to 700 nm. For example, 470 nm represents a blue light whereas 630 nm represents a red light.

Change Over Time

Nature’s evolution over time is a beautiful thing to behold, and it warrants taking the time to properly understand the phenomenon. This section deals with the spectral transformations and intensity variations in natural light that engender periodic changes in Nature. The following explains the way solar fires dictate days and seasons according to latitude, which results from the Earth’s rotation and orbit.

ASTM INTERNATIONAL (2005). Astm g159-98, standard tables for references solar spectral irradiance at air mass 1.5: Direct normal and hemispherical for a 37 degrees tilted surface. Rapport technique, ASTM. 8.

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