The Physics behind “Reflection with Color”

Color, Light, & the Human Eye

In 1672, Isaac Newton discovered that light can be split into different colors by a prism. In his experiment, he passes sunlight (which is essentially “white light”) through a glass prism, which produced a rainbow array of colors. He then passed the sunlight through a second prism and joined the two rainbows and produced white light once again. The colors produced by light penetrating the prism the first time (the rainbow) are arranged in a certain spectrum known as “ROYGBIV” where the letters each represent a color of the rainbow hue (red (R), orange (O), yellow (Y), green (G), blue (B), indigo (I), and violet (V)).

Each color possesses a different wavelength between approximately 400 and 700 nanometers (400 nm is around 15.74 x 10^-6 inches and 700 nm 27.56 x 10^-6 inches). When looking at the different colors of the rainbow, our eyes perceive many different wavelengths. Red light possesses longer waves (approximately 700 nanometers). Yellow light possesses a short wavelength (approximately 590 nanometers). When all wavelengths of visible light strike the eye all at once, white light appears.

Sensitivity of the Human Eye

Inside the human eye, there are special cells called cones and rods that sense brightness and color of visible light. Cones observe color and rods are only sensitive to a low amount of light, such as night vision. Our eyes are most sensitive to the colors between yellow and green. When a photon penetrates the human eye, the cones translate the photon’s energy into a nerve signal in your brain that tells you what color you perceive. Our cones are separated into three different types of photoreceptors that are most sensitive to the colors red, green, and blue. The different cones are called cone R, cone G, and cone B. Cone R is most sensitive to red-orange light, cone G is most sensitive to green-yellow light, and cone B is most sensitive to blue light.

How Fluorescent Tubes Work

When the lamp is turned on, the electrical current passes through the pins to the electrodes. Electrons then move through the inert gases found in the glass (which can include from neon, krypton, and argon). The current causes some of the mercury in the bulb to change from liquid to gas. Some of the electrons then collide with the gaseous mercury atoms causing the atoms to become excited which means the electrons move to a higher energy level. When the electrons return to their ground state, photons of ultraviolet light are emitted. These UV photons cause the atoms in the phosphor to become excited. When the phosphor atom returns to its ground state, photons of visible light are emitted. This process of converting invisible UV light to visible light is called fluorescence. The light is emitted in narrow spectral bands. Because the light triggers all three of our cones (cone R, cone G, and cone B) equally, we perceive white light.

Light Absorption, Transmission, & Scattering

The light tubes in this art piece are not colored themselves, but are white tubes placed in plastic sleeves. When light from the fluorescent tube hits the plastic sleeve, light is either absorbed, scattered, or transmitted. The incident rays hit the tube and some of the light’s energy is absorbed into the plastic material. Red or yellow light is then transmitted, which means that the light is emitted through the plastic sleeves onto the wall. It moves in the same direction as the incident light which is the light that hits the plastic. There is also other light that is emitted, which is called scattered light, which sends light out in different directions than the incident light.