What Even Is Light?
By definition, light is a form of electromagnetic energy. Electromagnetic energy is the result of an excited source and it radiates in waves.
I know... we are getting crazy with the science talk... let's break it down a bit.
Electrons change from one state to another when a radiant source is excited, releasing photons. These photons are tiny particles of energy radiating from that source in a straight direction but pulsating in a measurable wave. The distance over which the wave completes a full cycle is known as the wavelength and is typically measured in nanometers (nm).
The light we can see is a small range of electronic energy, from around 380nm to 700nm (also called the visible spectrum). Most electromagnetic energy is not visible, such as X-rays, radio signals, infrared light, cosmic rays, etc. Check out below the full range of measured wavelengths.
Seeing "White" Light
The sun (and who knows what else is out there) is constantly dumping loads of radiant energy onto our planet. Our atmosphere absorbs much of it, keeping the planet's surface inhabitable. One sliver of energy that is allowed through happens to be the visible spectrum. The presence of all of the billions of different wavelengths within the visible range combines into what we perceive as "White Light" around us. You can reverse engineer this and refract sunlight through a prism to see a rainbow - or all of the different wavelengths of the visible spectrum spread out.
Our eyes are developed to make sense of the radiant energy our atmosphere lets pass through. In our retinas are millions of cones ready to receive and react to a limited range of visible wavelengths within the visible spectrum. There are three different kinds of cones in our eyes:
L (long) - responds to wavelengths around 570nm
M (medium) - responds to wavelengths around 540nm
S (short) - responds to wavelengths around 430nm
These cones respond to a narrow range of wavelengths. It is no accident that these wavelengths are centralized around some pretty significant colors in the world of light and color: Red (L), Green (M), and Blue (S). So let's say you glance at a fruit, and when you do, your L cones respond strongly, but your M and S cones don't... you might be looking at a delicious red apple. 🍎
Color & Your Brain
Typically when we think about color, we assume the color is characteristic of the object. In reality, color exists only in your brain.🤯 Let's talk about what is happening when you're looking at that delicious red apple.
Let's assume we are looking at this apple outside - with perfect sunlight and the entire visible spectrum around us. For an apple to appear red to us, it must absorb all the green and blue wavelengths from the sunlight and reflect the reds. The red wavelengths are received by the cones in our eyes, giving us the perception of the apple appearing red.
Rods & Cones
All human vision systems are similar but not identical. We each have nearly 4.5 million cones arranged uniquely - like a fingerprint. Additionally, personal and cultural associations may alter how an individual perceives specific colors. For both reasons, each person's reaction to the color of any object is unique.
In addition to the three different types of cones in our eyes, a fourth type of cell detects the brightness around us. These are called rods. We have about 90 million rods in each eye, making our ability to perceive brightness much more detailed than color. Rods are very susceptible to energy; they can even react to as much as a single photon.
The rods, unlike their color-sensitive counterparts known as cones, are specialized cells that excel in low-light conditions. They act as the unsung heroes of our visual perception, allowing us to navigate dimly lit spaces and appreciate the subtleties of shadow and contrast. When you find yourself in a darkened theater, awaiting the curtain to rise, it's the rods that take center stage, whisking away the darkness and paving the way for the spectacle to unfold.
On average, a human eye typically contains around 120 million rods. These rods are primarily concentrated in the peripheral areas of the retina, which is why our peripheral vision is more sensitive to changes in brightness and motion detection. The central part of the retina, known as the fovea, contains a high concentration of cones, which are responsible for color vision and visual acuity. However, it's important to note that the exact number of rods can vary from person to person, making everyones experience with luminance unique.