Red is a color that is everywhere in our world, from traffic signals to ambulance and police vehicle sirens. The reason behind this is that the wavelength of red light makes it the least scattered color for the human eye.

During my drive back home the other day, I found myself stopped at a traffic signal, waiting for the signal color to change from red. This made me wonder, why is red used? Why not blue? Or just the regular white color of an LED?

Red can be seen almost everywhere, from alarm bells to the guards’ red flags at train stations, and even the rear lights of a vehicle when the brakes are applied. It may go unnoticed most of the time, but it becomes very noticeable in important situations. So, what is it about red that makes it the universal choice for police vans, ambulances, and other warning signals?

While many associate the color red with romance, symbolizing it through roses and heart-shaped stickers, its significance goes beyond that in our daily lives. In fact, red is the color of the blood flowing through our veins and arteries, albeit in a slightly different shade.

Why is Red Unique?

Our visual perception is highly attuned to the color red. (Photo Credit: udaix/Shutterstock)

As usual, scientific inquiry will aid us in unraveling this mystery!

To begin with, it is important to comprehend that the color red is one of the components found within the visible spectrum of light, known as VIBGYOR. This spectrum is formed by the separation of white-colored light waves.

Light waves possess a characteristic known as wavelength. In accordance with the wave theory of light, the wavelength (lambda: λ) of any wave is the measurement between two consecutive crests or troughs. Wavelength is determined by multiplying the wave’s velocity with its frequency. It is widely recognized that the speed of light is 3×10^8m/s.

Understanding frequency can be a bit more challenging. Frequency is the inverse of the time it takes for the wave to travel the distance of one complete wavelength.

The different constituents of a wave. (Photo Credit: Kicky_princess/Shutterstock)

Definition of Scattering

Scattering is the process in which light is deflected from its original path when it encounters an obstacle, such as dust, gas molecules, or water vapor. This redirection of light occurs when it interacts with the particles present in the surrounding medium.

Rayleigh’s Scattering and its Law

There exists a phenomenon known as scattering, which is regulated by a principle called Rayleigh’s scattering. This principle asserts that the scattering of light is directly related to the fourth power of the wavelength of light.

The intensity of scattering is directly proportional to the fourth power of the wavelength.

Should Our Warning Signals Scatter?

Consider this… do we desire our warning signals or alarms to be easily seen from a distance? Absolutely.

Any signals that are important and need to be noticed, such as danger or alarm signals, should use a color that can be seen from far away in order to notify people and prevent accidents. Therefore, we require light that doesn’t scatter much and is within the visible range for humans; otherwise, how would we be able to perceive it?

Within the electromagnetic spectrum, the range that humans can see is referred to as the “visible range” of light. This range spans from the color blue (which has the shortest wavelength) to the color red (which has the longest wavelength). The wavelength of red light is approximately 620-750 nm. The Scattering Law states that the color with the longest wavelength will scatter the least. Red satisfies both of these conditions: firstly, it falls within the visible range for humans, and secondly, it has the longest wavelength, making it the color that scatters the least.

Even in wet and foggy conditions, it is important for distress or alarm signals to remain visible. The visibility can be affected by circumstances such as fog, rain, and smoke. In order for the signal to reach a greater distance, it needs to scatter less. To achieve this, the wavelength of the signal should be high, which is why red is commonly used. Red is able to easily pass through fog, smoke, and other obstacles. This is why red is considered to be a reliable choice in such situations.

The Impact of Red on the Human Brain

According to a study published in the journal “Frontiers in Human Neuroscience,” the color red has been linked to attracting attention in an emotional context. The human brain immediately becomes vigilant upon seeing red.

Effects of Color on Motor Responses

Motor responses refer to the reactions exhibited by the human mind and body when subjected to various forms of stimulation. A research study has demonstrated that when individuals perceive the color red prior to or during a motor response, the intensity and speed of the response are enhanced. Nonetheless, a separate investigation has revealed contrasting results, indicating that exposure to the color red before engaging in a motor task actually impedes motor responses. The researchers propose that this inhibition is attributed to the evocation of fear.

Furthermore, there is evidence to suggest that the color red has the ability to evoke emotions. Studies have indicated that individuals often connect red with negative emotions, as it is commonly associated with fire, blood, anger, and occasionally with poisonous or hazardous creatures. (Source)

As a result, the human mind is immediately activated or alerted when it perceives this color. It has been established that signaling is one of the primary functions of a color. Therefore, the color red should be able to grab our attention, especially in emotional situations. Based on the aforementioned research, it appears that red effectively fulfills its role in the human brain.

Impact of Red in the Wilderness

In the wilderness and broader world, red is easily noticeable. (Photo Credit: twenty20)

When examining the effects of this color in the natural world, we discover that it is equally significant in terms of signaling. It can be easily seen against the blue backdrop of the sky and amidst green foliage. Prey can recognize a red-colored predator approaching them. Similarly, it is effortless to spot a red-hued prey moving or crawling near green leaves. Additionally, we can attribute most of the red flowers, which are highly valued in cultivation, to bird pollination. Birds are often attracted to the color red. Conversely, insects are drawn to white, yellow, and blue colors. It seems like the natural world has already conducted its own study of physics…

To attract our immediate focus, significant notifications are displayed in the color red

To summarize, although we often underestimate the significance of the red color in everyday situations, it is rarely disregarded in critical or urgent circumstances. Therefore, the next time you come across a traffic light, pay attention to your reaction to the color red, even if you don’t consciously notice it!