Time and the Color of Sunlight
The color of sunlight is linked to time of day. Humans have an innate sense of time based on the color and position of the sun. My design concept developed from the principle of how the color of sunlight changes throughout the day. The piece I designed works with this idea to bring a sense of passing time to artificial light.
The color of sunlight varies based on the sun's position in the sky. At midday, when the sun is most directly overhead, the light has to travel through the least amount of atmosphere and only the shortest wavelengths of light are scattered (i.e blue light) and the sun appears white. At sunset, the sun is low in the sky and the light has to travel through much more atmosphere to reach our eyes. The only wavelengths that make it through the atmosphere without scattering are the longest, orange and red. This is why the sun appears red at sunset.
This project began with material research to find or make a material that could scatter light as the atmosphere does with sunlight. To change the color of the light through scattering, suspended particles must be small relative to the wavelength of visible light. The shorter the wavelength of light, the more that color is scattered. Blue light, which has a wavelength of about 450 nanometers, is scattered first and the last to scatter is red light which has the longest wavelength at 700 nanometers. This type of scattering is called Rayleigh scattering.
Visual Properties of Rayleigh Scattering Materials
Using a PET film that exhibited Rayleigh scattering, I began experimenting. The more layers, the longer the wavelength of light that is scattered. Therefore, by increasing the number of layers of the film, the color of the light can gradually change from white to red just like sunlight throughout the day. Using this principle, I experimented with forms and orientations for the piece.
Kinetics and Arduino Control
The bulb moves up and down in the tower behind the layers of film. The movement is Arduino controlled to follow the movement of the sun.
Final prototype showing the color and position of the light changing throughout the day, from red-orange at sunrise to white at midday and returning to red-orange at sunset.