Understanding the Visible Light Spectrum and Color

One aspect of light that is important to understand is the Visible Light Spectrum. As the name suggests, this is the segment the human eye can see. It is a narrow band within the Electromagnetic Spectrum. While scientists continue to debate about our world view or zeitgeist, there are a number of established principles and properties that can reveal the nature of light. An examination of the various forms of light can provide you with a solid base and understanding of light, as you create light plans for your current projects.

Electromagnetic Radiation

Electromagnetic radiation is a form of energy. Electromagnetic radiation helps with plant photosynthesis and with zooplankton biosynthesis in our oceans, it can be converted into solar power, and it allows us to see a variety of colors. The human eye cannot see all forms of electromagnetic radiation. What we can see is called the Visible Spectrum.

The large range of frequencies within EM Radiation is a classification called the Electromagnetic Spectrum. You will recognize many of the various regions of the EM Spectrum. From low to high frequency range:

• Radio
• Microwaves
• Infrared (IR)
• Visible Light
• Ultraviolet (UV)
• X-Ray
• Gamma Ray

All of these frequencies are present in your daily life. Aside from LED light bulbs which sit inside the Visible Light Spectrum, you can listen to music over radio waves, your doctor performs x-rays to view broken bones, and you may have heated your lunch with the energy produced by the microwave spectrum.

The frequencies for UV, X-Ray and Gamma, which are outside the Visible Spectrum, are a harmful type of radiation to living organisms. They operate at high frequencies, which means high energy is involved. Because of the Earth’s protective atmosphere, which absorbs gamma rays, we on the planet are protected from those harmful radiation waves. This is one reason why addressing climate change, and making choices to help create a sustainable future is important.

The word “wave” often brings to mind our magnificent ocean waves. When we examine the definition of a wave, we find a wave refers to the disturbance in a physical medium or field that results in an oscillation or vibration. This is shown in the ocean with the swell or crest and then a valley or trough of water. Electromagnetic waves oscillate perpendicular to one another in a wave format unique to its specific frequency.

Electromagnetic waves can travel through a vacuum. By contrast, mechanical waves only transport energy via a medium. Energy is transported by electromagnetic waves through outer space. Vibrating an electric charge produces electromagnetic waves.

Measuring Light

How we measure light is as important as its properties. Because light travels in waves over time, similar to waves in the ocean, we can measure the distance traveled by looking at the wavelength.

The point where the wave creates a dividing line, where an equal visual weight appears on each side (crest and trough) is called the central axis. Think of the central axis of a wave as the horizontal distance. Waves crest (up) and trough (down) on either side of that central axis when shown during the passage of time. A single wavelength is measured as the distance between two consecutive toughs or crests.

Amplitude is associated with the brightness or intensity of a wave and is measured from the central axis up to the midpoint of the crest.

The frequency of a wave is the number of full wavelengths (one crest and one trough) that pass a given point in space each second. This is usually measured in cycles per second or hertz. When talking about light, we refer to the frequency in terms of color.

Electromagnetic waves within the Visible Spectrum are tiny. NASA equates these waves to the size of a virus. The energy of visible light received by your retina is interpreted by your brain as color.

Scientists use the various waves in the EM Spectrum to measure and study our universe. Each type of light tells us unique things. This is particularly useful when we examine the lightwaves captured by the Hubble telescope or even when we look at light beams here on Earth.

In the world of lighting, we look at the properties of light to define what we need in each lighting application scenario. You can download specific technical specifications about our lights to learn more detail about each one or you can view those tech specs on our individual product pages. In studying the physics of light, there are other formulas and properties we can examine.

Properties of Light in Physics

Quite a few physics formulas help us define the properties of light. One of the main ones describes the relationship between speed, wavelength, and frequency. Use this Wave Speed Formula to calculate wave speed, when wavelength and frequency are known.

There is an inverse relationship between light wavelength and frequency. Because the speed of a light wave is constant in this equation, the wavelength and frequency are the only things that change.

Wave Speed Formula:

Speed = Wavelength x Frequency

Wavelength is measured in meters or in the case of light in nanometers (nm).

Frequency is measured in hertz (Hz), the number of waves per second. With light we measure in Tetrahertz (THz).

The above formula also shows you that when wavelength increases, frequency must decrease. The same applies in reverse. This is what is meant by an inverse relationship. If your frequency (energy) increases, then the wavelength decreases.

As mentioned, there are quite a few formulas you can review that affect light. We will dive more into the wave properties of wavelength, amplitude, and frequency in future detailed blogs about light. We can now examine the narrow band of the Visible Light Spectrum.

The Visible Light Spectrum

Our understanding of light continues to expand as humanity studies the properties of light and color. Electric lights were built upon the foundations of the principals discovered by scientists over the centuries. As our comprehension of the physical world became more refined over time, we adjusted and developed even more complex lights, such as LEDs.

The modern scientific study of light began with Isaac Newton’s experiments with a prism, which revealed the refraction of sunlight into what he saw as a rainbow. Newton stated that light was comprised of colored particles. About twenty years later, a Dutch physicist and astronomer proclaimed his theory that light was a wave. It wasn’t until almost a century after Newton that James Clerk Maxwell discovered that light was a form of electromagnetic radiation (EM). In early 1905 (prior to his special relativity announcements), Albert Einstein proposed the quantum theory of light and photons. In it, he proposed the idea that light is a flow of elementary particles or tiny packets. It wasn’t until 1926 that Gilbert N. Lewis coined the phrase photon that is now associated with Einstein.

Let’s examine the early studies of light, then learn more about the properties of the Visible Spectrum.

As Sir Isaac Newton showed in his optics experiments back in the 1660s, when you disperse sunlight through a prism, white light will separate into different wavelengths. His experiments laid the groundwork for studying color in a scientific manner and represents the geometrical model of light.

Newton’s experiment demonstrated the composition of light in seven visible colors in the form of a rainbow. As a mnemonic, we refer to the order of these rainbow colors as ROY G BV in America and in Britain you use “Richard Of York Gave Battle in Vain.”

Red (R) Orange (O) Yellow (Y) Green (G) Blue (B) Violet (V) *

[* NOTE: In modern science, indigo is not classified as its own color. This sequence used to be ROY G BIV. Indigo was removed since many people cannot distinguish it visually as its own color. It is now a tertiary color and the wavelengths are wrapped into the Violet range.]

Each of these colors represents an individual wavelength. We perceive a specific color when that particular wavelength strikes the retina of our eye. This process involves a stimulation of the retina, which our brain then interprets as a color.

Each color is unique and has its own properties. In a 1665 experiment, Newton showed that depending on the wavelength of the color, each color refracts at a slightly different angle.

High frequency waves are closer together and considered as short, due to the time involved to view one wave. Low frequencies are long and the waves appear to spread out more, visually.

Here are the wavelengths at the edges of the visible region of the Electromagnetic Spectrum:

• Red Light (the longest wavelength)
• Violet Light (the shortest wavelength)

If the Visible Light Spectrum is a rainbow, where does sunlight appear?

Sunlight appears in what we call 'white light'. In LED lighting, we refer to it as Daylight (5000K). This is white light that is equal to the quality of light you would see during a sunny day. However, white light is not a color. It is a combination of all colors in the Visible Spectrum. The color temperature assigned to match sunlight is 5000° Kelvin. The Kelvin scale measures Correlated Color Temperature (CCT). This is a way to measure a light’s appearance in the warmth or coolness of the light emitted. We’ll discuss this further in next week’s blog about the Color of Light. You can learn more about color temperatures in our Lighting 101 page.

Black does not fall on the Visible Light Spectrum. Black is a lack of light. Each color we perceive from the VLS is unique, as is its wavelength and frequency. 

Color Wavelengths and Frequencies

Where one color starts and another begins, when comparing the colors that make up the visible spectrum, has been debated often in scientific communities. The color chart below lists approximate measurements, since these numbers vary slightly depending on the report consulted.

The wavelength of each color is measured in nanometers.

Frequency is shown in terahertz.

[NOTE: Indigo is a subset of violet in this representation. It falls with an approximate wavelength around 425-450nm and an approximate frequency of 670-700 THz.]

Understanding color and light quality will help make you a more informed consumer, whether purchasing for your home or your office. Color can affect our perception of how an object is seen. That is one reason why a high CRI is important when considering which LED light to purchase. A high CRI provides an accurate color rendering of the items in your office or home. If you have a fascination with light and want to know more about Light Quality & You, check out our early blog on the subject.

Our next blog will cover the Color of Light and CCT.