That bright blue LED light, found on many electronic devices, may be the cause of eye strain, headaches and even sleep disruption.

Blue light causes more trouble for the eye than other colors. That is because it is harder for the eye to focus blue sharply. Different wavelengths of light (i.e. different colors) have different refractive indexes as they pass through the eyeball to the retina. Our eyes can easily focus on fine details in red or green light.

But our retinas can’t handle blue light very well. Blue light scatters more widely within the eye and tends to be focused in front of the retina, making it appear slightly out of focus. What we notice is a kind of halo around bright blue lights. They also seem to produce more glare. So blue light can lead to eye strain and headaches as your eye muscles strain to bring fine details into focus.

The problem is compounded when the light source is an LED. Because of a difference in the manufacturing process, blue LEDs are different from other colors. They can be up to 20 times brighter than traditional red or green LEDs.

Blue lights are more noticeable in the dark or in dim light because the rods (a type of photoreceptor in the retina) are most sensitive to greenish-blue light. And since there are more rods in the outer edge of the retina, blue lights appear brighter in our peripheral vision in low-light conditions. That’s why a tiny blue LED can be so distracting in a dark room, even if it’s in your peripheral vision.

But beyond being a distraction, blue lights are known to affect our circadian rhythm and sleep patterns. Exposure to blue light suppresses the production of melatonin. Melatonin is known as the “sleep hormone” and is produced by the pineal gland, a pea-sized gland in the middle of your brain. You sleep when melatonin levels are high and awaken when melatonin drops.

Even a very low level of blue light, such as that produced by a single bright LED, can suppress melatonin levels, leading to wakefulness. This means anything with a blue LED in your bedroom has the potential of disrupting your sleep cycle. This can be the tiny blue light on your phone charger, the power button of your laptop, or accessories such as speaker lights. If this is the case, try unplugging the device, removing it to another room, or covering the LED so you can’t see the light. You may sleep better for it.

Delia Treaster, Ph.D., is a certified professional ergonomist and writes on various ergonomic issues, drawing on decades of experience in occupational ergonomics. She has been an ergonomic contractor with Humantech, one of the largest workplace ergonomics consulting firms in the United States. Prior to working for Humantech, Delia was an ergonomic consultant for the U.S. Postal Service, a senior ergonomic specialist with Travelers Insurance, and a research scientist at Battelle Memorial Institute. She has a master’s degree in human factors engineering and a Ph.D. in biomechanics from Ohio State University.

E-mails to Delia can be sent to

Editor’s note: “Ergo Corner” is part of a series of guest spots by industry experts that will appear regularly on ASSEMBLY’s blog page. Check back frequently to read more commentaries from Delia, as well as contributions on product testing, automated assembly systems, electronics assembly and robotics.