Which Energy Helps Us To See?

Vision is the sense that allows humans and other animals to see the world around them. This incredible ability relies on visible light, which is part of the electromagnetic spectrum. The electromagnetic spectrum encompasses all electromagnetic radiation, from radio waves to gamma rays. Visible light represents a very small slice of this spectrum that human eyes can detect. When visible light enters our eyes, it makes vision possible by triggering specialized cells in the retina to send signals to the brain. The narrow band of visible light wavelengths allows us to perceive color, brightness, and images of the world around us.

The Electromagnetic Spectrum

According to NASA, the electromagnetic spectrum is the full range of electromagnetic radiation that exists, organized by frequency and wavelength [1]. It encompasses all forms of light energy, including gamma rays, X-rays, ultraviolet light, visible light, infrared light, microwaves and radio waves. While the entire electromagnetic spectrum is electromagnetic radiation, it is categorized into different types based on frequency and wavelength.

Visible light is the part of the electromagnetic spectrum that is visible to the human eye. As Wikipedia explains, visible light is usually defined as having wavelengths in the range of 400–700 nanometers (nm), corresponding to frequencies between 430–750 terahertz [2]. This range represents a tiny portion of the electromagnetic spectrum between infrared light and ultraviolet light. While visible light allows humans to see, the other types of electromagnetic radiation that exist above and below visible light are imperceptible to the human eye.

Visible Light Properties

Visible light is the part of the electromagnetic spectrum that is visible to the human eye. The wavelength of visible light ranges from about 380 nanometers to about 740 nanometers (Visible Light Spectrum, Wavelength & Frequency). The frequency of visible light falls between 430 trillion hertz and 770 trillion hertz. This range of wavelengths/frequencies is visible because it matches the spectral sensitivity of the rods and cones in the human eye.

Visible light has shorter wavelengths and higher frequencies than other forms of electromagnetic radiation like infrared, microwaves, and radio waves. For example, the wavelength of infrared radiation can be over 1 millimeter, whereas visible light wavelengths are measured in the hundreds of nanometers. The higher frequency of visible light means it contains more energy than lower frequency forms of EM radiation. This energy allows visible light to be detected by the human eye.

The Human Eye

The human eye is a complex organ capable of detecting light and converting it into electro-chemical impulses to the brain, which then interprets it as visible images. The eye has several important parts that work together to achieve this function.

Light first enters the eye through the cornea, the transparent covering at the front of the eye. The cornea helps focus light rays as they pass through. Behind the cornea is the iris, which controls the size of the pupil to regulate the amount of light entering the eye. The pupil appears black because it is an opening that allows light to enter the eye.

After passing through the pupil, light rays are focused by the lens onto the retina at the back of the eye. The retina contains photoreceptor cells called rods and cones that detect light and convert it into electrical signals. Rods work in low light conditions and detect brightness and motion. Cones work in bright light and allow us to see color. The central part of the retina is called the macula and contains mostly cones.

The conversion of light into electrical signals happens in the rods and cones. The signals are then sent through the optic nerve to the visual cortex in the brain, which processes these signals into the images we see. This allows us to see the world around us through visible light entering our eyes.

[Source: https://www.elmanretina.com/services/human-eye-anatomy/]

Light Detection

Light enters the eye through the cornea, which helps focus the incoming light. The light then passes through the pupil, which can constrict to limit light or dilate to allow more light in. The light is further focused by the lens onto the retina at the back of the eye. The retina contains two types of photoreceptor cells that detect light – rods and cones. Rods are responsible for low light vision, while cones allow for color vision. Cones are concentrated in the fovea at the center of the retina. As light hits the photoreceptors, it causes a chemical reaction that generates an electrical signal. This signal then travels through the optic nerve to the visual processing centers in the brain, allowing us to see [1] [2].

Visual Processing

The visual signals received by the eyes must be transmitted to the brain for processing into the images we see. The optic nerves carry signals from each eye to the optic chiasm, where some fibers cross over to the other side of the brain. From there, signals travel via the optic tracts to the lateral geniculate nuclei in the thalamus, which act as relay stations. The thalamus then sends the signals to the primary visual cortex located at the rear of the brain. From the primary visual cortex, two pathways transmit signals to higher cortical areas for further processing:

The ventral stream (also called the “what pathway”) travels into the temporal lobe and is associated with object recognition and form representation. The dorsal stream (or “where pathway”) goes into the parietal lobe and is involved in guiding actions visually and processing spatial locations. In the visual processing areas, the brain analyzes patterns, movement, color, and depth to build up a coherent picture of the surrounding environment. Focus, attention, and memory functions also facilitate visual processing and interpretation of incoming signals.[1]

Although raw visual data starts in the eyes, complex processing in multiple areas of the brain transforms simple signals into the seamless, detailed images we perceive. The visual system essentially reconstructs the visual world from limited sensory inputs.[2]

[1] https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Book%3A_General_Biology_(Boundless)/36%3A_Sensory_Systems/36.15%3A_Vision_-_Visual_Processing

[2] https://www.readworks.org/article/Visual-Processing-in-the-Brain/b9f8c73c-38a5-4ca9-b81b-dd51a8c149f7

Color Vision

Color vision allows us to see the different wavelengths of light and discriminate between objects based on their color. This ability is enabled by special photoreceptor cells in the retina called cones. Cones contain light-sensitive pigments that are tuned to be most sensitive to specific wavelengths of light corresponding to red, green, and blue (1). There are three main types of cones:

  • L-cones that detect long wavelength light like red
  • M-cones that detect medium wavelength light like green
  • S-cones that detect short wavelength light like blue

The brain processes signals from the three different cone types to perceive a wide array of colors. This trichromatic theory explains how the combination of signals from cones sensitive to red, green and blue (the primary colors) enables us to see the full spectrum of visible colors (2). The relative activation of the different cone types allows the brain to differentiate between millions of colors.

Common Vision Problems

Many people experience vision problems at some point in their lives. Some of the most common vision disorders include:

Refractive Errors

Refractive errors occur when the shape of the eye prevents light from focusing directly on the retina. This results in blurred vision. Common refractive errors include:

  • Nearsightedness (myopia) – objects far away appear blurry
  • Farsightedness (hyperopia) – objects up close appear blurry
  • Astigmatism – blurred vision at any distance due to an irregular cornea

Refractive errors can often be corrected with prescription eyeglasses or contact lenses.

Color Blindness

Color blindness is the inability to distinguish certain shades of color. The most common type is red-green color blindness where people have trouble differentiating between reds, greens, browns, and oranges. Color blindness is generally an inherited condition and more prevalent in males than females.


A cataract is a clouding of the normally clear lens of the eye. As cataracts develop, vision becomes increasingly blurry. Cataracts typically develop slowly and can eventually lead to blindness if left untreated. Cataracts are very common, especially in older adults.

Cataracts are treated through surgery to remove the clouded lens and replace it with an artificial lens implant to restore vision.

Protecting Vision

There are several ways to help protect eye health and vision. Getting regular eye exams is crucial to catch any potential vision issues early. Comprehensive eye exams can detect eye diseases like glaucoma or cataracts before major vision loss occurs (Ocuvite > Home).

Wearing proper eyewear like prescription glasses or sunglasses is also important. Sunglasses that block 99-100% of UVA/UVB rays can help reduce sun damage to the eyes that can lead to cataracts or macular degeneration later in life (5 top tips for protecting eye health).

Following a healthy diet rich in eye-boosting nutrients can support good vision. Foods like leafy greens, citrus fruits, nuts, seeds, eggs and fatty fish provide key antioxidants like lutein and zeaxanthin that may help lower risks of age-related eye diseases (Protecting Eye Health and Possibly Reducing Your Risk for Developing Macular Degeneration).

Reducing eye strain from digital devices is another way to protect vision. Using the 20-20-20 rule (looking away every 20 minutes for 20 seconds at something 20 feet away) gives eyes a break. Adjusting screen brightness, increasing text size, and using blue light filtering lenses can also minimize fatigue and irritation.


In summary, visible light energy allows humans to see through a complex process involving the eyes and brain. Light waves in the visible spectrum, with wavelengths of 400-700 nanometers, enter the eye through the cornea and pupil. The lens focuses this light onto the retina, which contains photoreceptor cells called rods and cones. Rods detect low light levels and motion, while cones detect color and fine details. The retina transforms the light into electrical signals that travel through the optic nerve to the visual cortex in the brain. Here, the signals are processed into the images we perceive. Factors like lighting conditions, eye health, and visual pathway function all contribute to normal color and sharp vision. Understanding the biological mechanisms behind sight reinforces the wonder of our ability to visually interpret the world around us.

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