Please ensure Javascript is enabled for purposes of website accessibility How Much Light is Required for Good Vision?
Dr. D. Y. Patil Vidyapeeth, Pune
(Deemed to be University)
Dr. D. Y. Patil Institute of Optometry & Visual Sciences
Pimpri, Pune-411 018 (Maharashtra) India.

How Much Light is Required for Good Vision?

How Much Light is Required for Good Vision?

Optimal Lighting for Eye Health: Balancing Comfort & Function. Discover how light affects your eyes and learn to create a vision-friendly environment.

Ms. Tanaya Dalvi (Asst. Prof.)
August, 12 2023

Have you ever faced a problem while reading or working in inadequate light? If yes, it often must have left you with a headache or eye strain after prolonged hours of work in dim light. For eye-related problems like this, light is the problem and light is the solution.

The sources of light on Earth – the sun, fire, and powered light – make up a small portion of the entire electromagnetic spectrum. Out of these, our eyes are most sensitive to the yellowish-green light of wavelength 555nm in the visible spectrum. The rest of the electromagnetic radiation gets absorbed by the cornea, the lens, and the retina. The cornea and the lens absorb the UV rays, thus only visible and Infrared A reach the retina, and more so in children than in adults.

So, what is the required amount of light for us to see?

Various researchers have defined 2000 cd/m2, 2500 cd/m2, and 2800 cd/m2 as luminance thresholds for visual comfort when an occupant's view direction is parallel to windows. A higher luminance threshold range of 2740 cd/m2 and 6000 cd/m2, or lower luminance thresholds of 1500 cd/m2, 1800 cd/m2, and 1920 cd/m2, can cause visual discomfort in the same view direction.

Any sources of glare (i.e., window location) in the eye's field of view (FOV) can also cause visual discomfort.

While reading in a room, if the screen and the surrounding light are quite different (either brighter or darker), your eyes will constantly readjust between the surrounding light and the screen each time you look away from the screen. Even if your eyes have adjusted to the screen illumination, whenever you look elsewhere, your eyes will need to readjust to this change in contrast. Therefore, when you look back at your screen, you will no longer have good sharp vision until a few minutes have passed.

It is not only the level of illumination that matters, but also the type and colour of light. Natural sunlight is always healthier than artificial lighting, regardless of the type of light bulb you use. Spending at least 10 to 20 minutes per day outside will increase the creation of serotonin and vitamin D, thus leaving you with stronger bones and clearer vision.

Your eyes will feel more relaxed in the soothing glow of yellow or warm light. This makes it a brilliant choice for reading or engaging in tasks that require mental stability. Whether it's your cozy living room or your peaceful bedroom, these spaces are perfect for unwinding and immersing yourself in a good book. The beauty of this light is that it won't disrupt your body's melatonin production, unlike cooler light. Your brain associates yellow light with the calming ambiance of a sunset, creating a sense of tranquillity and ease.

On the other hand, white light is known for its cold, energetic, and direct nature. It enhances your ability to concentrate and stay focused throughout the day, making it ideal for workplace settings or commercial spaces. Cold light can even boost your learning capabilities. If bright white light strains your eyes, a softer yellowish-white light would do just fine. However, it's important to consider that excessive exposure to intense cold light can make one feel overly alert, resulting in a decline in performance. Over time, relying heavily on LEDs can prove detrimental, leaving you feeling exhausted and irritable by the end of the day.

Unfortunately, the modern world inundates us with excessive blue light through TV screens, 6,500 K light bulbs, cell phones, and monitors. It's important to note that bluish cold light always exceeds 5,000 K. Prolonged exposure to blue light at night can disrupt your sleep cycles, while continuous exposure can even lead to permanent eye damage.

What happens in case of inadequate light?

What happens when lighting is inadequate?

Human vision is truly remarkable, thanks to its incredible adaptability influenced by both environmental and physiological factors. Have you ever noticed how your vision seems to momentarily decline when you experience eye fatigue? It appears that when you shift your gaze from a screen to a different location in a room with varying lighting, your pupils either dilate or contract, depending on the ambient light. This constant adjustment can strain the muscles in your eyes, resulting in that unpleasant feeling of eye fatigue. Furthermore, it can prolong the time it takes for your eyes to adapt to a new setting.

Moreover, directly staring at bright lights can harm your precious eyes. When the light-sensing cells in your retina become overstimulated, they release an excessive amount of signalling chemicals, ultimately causing damage to the back of your eye.

Overexposure to light can lead to dysfunction or even irreversible tissue damage, either through excessive heat or photochemical reactions. Here are a few examples:

  • Exposure to the cornea can cause reversible lesions in the corneal epithelium, as well as lesions in the corneal stroma and the Bowman membrane, which may lead to corneal opacity and potentially result in corneal neovascularization.
  • On the conjunctiva, excessive exposure can lead to the development of pterygium (a non-cancerous growth on the conjunctiva) and conjunctival neoplasms.
  • Blue light can induce photodynamic damage in lenses that have accumulated photosensitive debris or drugs, potentially leading to the development of cataracts. Cortical cataracts have also been associated with UV exposure.

If you are an avid reader or find yourself glued to screens for most of the day, here's a nifty trick to give your eyes some relief. It's called the 20/20/20 rule. Simply put, every 20 minutes of reading, take a 20-second break and focus on something 20 feet away (6 m).

Remember, it can be challenging to catch eye issues early on, as one eye can compensate for the other until it's too late. Surprisingly, regular visits to an eye specialist can prevent up to 50% of all blindness, which is especially crucial for individuals with a family history of eye disease.

Furthermore, keep in mind that as time goes by, your eyes may become weaker. So, tailor the lighting in your home to your age, particularly your reading light for bedtime if you enjoy reading before sleep.

By understanding the impact of light on our eyes and taking appropriate measures to optimize our environment, we can maintain healthier and more vibrant vision.

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