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In the modern world, it’s common for people to spend huge chunks of their day staring at screens for work, essential tasks, entertainment and social interaction. Most of these screens are backlit LED screens that emit a high proportion of blue light, especially compared with older incandescent light bulbs and natural sunlight. Because people are spending so much time on computers, tablets and cell phones — often with their eyes just inches away from the screen — some eye care professionals are worried that this could cause lasting harm.

So, does blue light damage your eyes? How do blue light glasses work? Let’s explore.

Visible light is part of the electromagnetic spectrum. Within this spectrum, radio waves have the longest wavelengths and the least energy, followed by infrared light, visible light, ultraviolet light, X-rays and gamma rays, which have the shortest wavelengths and most energy. Within the visible spectrum, red light has the longest wavelengths and least energy, followed by orange, yellow, green, blue, indigo and violet. The last three colors — blue, indigo and violet — are often grouped together as “blue.”

In the eye, light travels first through the cornea and then through the lens to reach the retina in the back. The retina contains rod cells that produce images in black and white (which is essential in low-light conditions) and cone cells to detect color (which is only possible in bright-light conditions). The cornea and lens block most UV light and prevent it from reaching the retina. Excessive exposure to UV light is known to damage the cornea and cause snow blindness, according to the American Academy of Ophthalmology. This exposure can also increase the risk of cataracts in the lens, as the National Eye Institute explains. Sunglasses with quality lenses can block 99%-100% of UV light and 75%-90% of visible light and are strongly recommended for anyone in bright sunlight.

Blue light is not blocked by the cornea or the lens — despite having just slightly longer wavelengths and slightly less energy than UV light. Most flat screen devices use a blue-light LED (peak emission of ~450-470nm) coupled with a yellow phosphor (peak emission ~580nm) to produce light that appears white, as the journal Molecular Vision describes. This color distribution is very different from that of natural sunlight.

Experiments have shown that blue light — more than other wavelengths of visible light — can damage retinal cells in Petri dishes and in laboratory rodents. However, these experiments are done with levels of blue light that far exceed what would be produced by a typical screen. For example, a 2018 study published in PLoS One exposed mice to bright white light (5,000 lux) for 24 hours a day for 7 days.

“Lux” is a measurement of light per surface area. Experts recommend about 300 lux for living rooms and between 500 and 800 lux for reading areas, according to ThoughtCo. The lux provided by a computer or tablet depends on the brightness setting and the distance to the user’s eyes. According to Elemental, desktop computers can provide anywhere between 0.5 and 37.8 lux. This is far below the 5,000 lux used in the 2018 PLoS One experiment and many similar experiments. As an additional point of reference, sunlight can provide around 100 lux on an overcast day and over 10,000 lux on a very bright day, according to the Engineering Toolbox. Therefore, sunlight provides far more blue light than LED screens.

While the laboratory experiments on blue light are extreme, some of the results are concerning because the retinal cell damage is similar to what is seen in age-related macular degeneration, which is a leading cause of vision loss in older adults.

The 2018 PLoS One experiment used a special filter that blocked 94% of blue light while allowing other wavelengths to flow through. More typical filters only block 30%-50% of blue light and also block other wavelengths to some extent. These filters work in the same way as sunglasses that block UV light. Many companies now offer glasses that block blue light and filters that can be placed over digital screens to block blue light.

The American Academy of Ophthalmology does not recommend any special blue light-blocking eyewear for computer use. This is because the available evidence doesn’t indicate that the amount of blue light produced by electronic devices harms the eye. Furthermore, blue light has many positive effects. It increases alertness, memory and cognitive function, and it treats seasonal depression.

Nonetheless, some people find that blue-light blocking glasses can decrease eye strain when viewing digital devices for long periods of time. Digital eye strain commonly results in dry, irritated eyes and difficulty focusing. This is temporary and can often be prevented by following the 20/20/20 rule: After every 20 minutes of computer time, focus on something about 20 feet away for 20 seconds.

Finally, blue light is known to suppress the production of melatonin hormone, which induces sleep. Many experts recommend turning off digital screens at least 30 minutes before bedtime.

Blue light is all around us, especially as our world becomes more digitized. But taking the proper precautions can help you keep your eyes protected.

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