19 Dec Is Blue Light Bad For Our Eyes?

Is blue light harmful to our eyes? In short, no. Although, it is much misunderstood. Natural daylight has a very high proportion of blue wavelength light at much higher intensities than we would normally be exposed to from our electronics and indoor lighting sources. Blue light by day is crucial for the correct working of our body clock, which governs the functioning of every tissue in the body. It is absorbed by specialised photoreceptors in the retina that transmit the time-of-day message to the master pacemaker in our brain. From there, the brain sends the message to every cell, similar to conducting an orchestra, so that all of our tissues and organs play to the same beat. This stimulation by blue light keeps our body clocks working in synchrony with the environment and keeps us healthy.

Recently there was some speculation that certain types of blue light could be associated with macular degeneration and other retinal issues. This related to very short wavelength light of approximately 410 nanometers (dark blue) and needed to be perceived by the sensitive retinal cells in very high intensities to cause damage. These results came from studies in mice and the jury is still out as to whether it is a cause for concern in humans (recently published papers contradict).

A much more important issue in relation to the perception of blue light is not the damage it might do to the retina, but the impact it has on our internal body clock when perceived at inappropriate times of day. As humans, we evolved over millennia continuously exposed to the 24 h light/dark cycles provided by a rotating planet. Our bodies have learned to use the regular transitions at dawn and dusk, blue-enriched light by day and darkness at night to keep our immune system, rest/activity cycles, heart rate, blood pressure, body temperature and almost all physiological functions working rhythmically with a 24 h (circadian) rhythm. Blue light may not be harmful to our eyes, but inappropriate exposure to blue light at night is harmful to our bodies. Shift workers, air stewards and frequent transmeridian travellers are often exposed to lighting at the wrong time of day and all experience disruptions to the normal functioning of their body clocks. This circadian disruption is known to contribute to the development of diabetes, cardio-vascular disease, mental health disorders, and even cancer.

In contrast, blue light used appropriately between the hours of dawn and dusk can help alleviate symptoms of depression and seasonal effective disorder – similar to the positive mood-lifting feeling you get on a sunny day. Similarly, for night shift workers, bright light exposure through the night, which is important for alertness and cognitive function, must be balanced with extended periods of darkness by day to facilitate rest and help keep the body clock functioning, but in the opposite phase to the environmental light cycle. “Nightshift workers who can work in environments with high-intensity light, or in light with a high colour temperature [more blue], will be more alert and perform better during night shifts. They will also sleep better once the night shift is over,” says Professor Ståle Pallesen, a leading researcher investigating methods to mitigate the negative consequences of shift work at the University of Bergen in Germany.

So the question of whether blue light is harmful really depends on the time of day that you are exposed to it, and, unless you are sitting in front of a very high-intensity lamp that emits dark blue light peaking around 410 nm, then the retinal cells in your eyes will be just fine. Soft blue light blinkers that provide extended daily light to horses for enhancing fertility and health are often worn for months at a time and emit 470 nm wavelength light. Scientific trials show no detrimental effects on the animals’ eye health from this following sustained use.

Blue filtering lenses may have their place when screen time is required at night, as they help to reduce the stimulating effects on the brain of LED light and allow the body to prepare for rest and sleep – a function that requires dim lighting within the yellow/red spectrum to allow the sleep-inducing hormone melatonin to rise. However, even these are not recommended by the American Academy of Opthalmology as blue light also has important benefits that contribute to general eye health. The best option for maintaining good health and sleep/rest rhythms is to provide yourself with at least 6 h of darkness or dim red light at night, while ensuring you are exposed to bright daylight or blue- containing artificial lighting during daytime or active hours. So, the next time you look up and appreciate the blue sky on a clear day, know that your body is thanking you too.

– B.A. Murphy, PhD