Why 248 Scientists Now Say Yes

By Dr. Martin Moore-Ede, MD, PhD
Co-discoverer of the suprachiasmatic nucleus, the master biological clock in the human brain. Founder of the Laboratory for Circadian Physiology at Harvard Medical School.

In 2023, 248 scientists who study light and health reached a consensus on twenty-five statements: the blue-rich LED lighting now standard in homes, offices, schools, and hospitals carries real health risks, and people have a right to be warned. The science behind that statement is no longer in serious dispute among the researchers who know it best. What is missing is not evidence. It is action.

I was one of those 248, and I want to explain plainly why a group of scientists, who disagree on many subjects, agreed on this.

What the consensus actually says

For most of the last few decades, the science of light and health looked messy from the outside.

Thousands of papers, some of them apparently in conflict, made it easy for anyone who preferred the status quo to say the jury was still out. But that messiness was the normal process of a young field sorting itself out, and it took about twenty years to resolve. What emerged on the other side is a clear scientific consensus: the spectral makeup, the brightness, and above all the timing of the light we live under have profound effects on human health. Bright blue-rich light during the day supports health. The same light after dark undermines it. That is the agreement the 248 of us reached.

So when someone tells you the science is not settled, they are describing the field as it looked twenty years ago, not as it is now.

Why a warning is justified

The case for warning people rests on a simple comparison that I do not make lightly.

We have been here before with other products that were sold for decades as harmless while the evidence of harm quietly accumulated. Tobacco. Asbestos. In each case the science arrived well before the regulation, and a great deal of avoidable harm happened in the gap between knowing and acting. Blue-rich light at night sits in that same uncomfortable space today. The World Health Organization has already classified the circadian disruption that night work causes as a probable human carcinogen. The links to breast and prostate cancer, to obesity, diabetes,
and heart disease, are documented in a large and independently replicated body of work. And yet you can buy the lighting that drives that disruption, by the armful, with nothing on the box to tell you.

A warning label would not ban anything. It would do what warnings do: let people make an informed choice with their own eyes open.

Why the lighting we have is stuck

If the science is clear, you might reasonably ask why nothing has changed. The answer is not mystery. It is inertia.

Our lighting is held in place by a deeply embedded status quo, by outdated laws, building codes, and lighting standards that were written around how a light looks and how cheaply it runs, never around what it does to the people beneath it. That framework gives us the same unchanging blue-pump LED light everywhere, all day and all night, and it resists change the way large embedded systems always do. The industry's favorite argument is that we should wait until the science is complete before changing the products. But science is never complete, and that is not a reason to keep selling something we already know causes harm. We know more than enough today to do better today.

There is even a problem inside the standards meant to measure healthy light. The most widely used metric was built partly on studies of people in the dark, which exaggerate the role of green light. In normal indoor conditions, once your eyes adjust, that green effect fades within a couple of hours. The metric is slowly being corrected, but because it is baked into existing standards and calculators, it lingers. Good science has to keep pushing against its own outdated versions, not only against industry.

What healthy lighting would look like

The hopeful part is that the fix is not exotic. We already know how to build it.

Healthy lighting means light that changes across the day the way daylight does: bright and blue- rich in the morning and working hours to keep your body clock strong, and blue-depleted after dark to protect the night. It means specifications written around the light source and its effect on the body, not just the lumens it emits or the watts it draws, reviewed and updated as the science advances. Manufacturers can build this. Much of the technology already exists. What has been missing is the demand, the standards, and the public understanding to pull it into the market.

That last piece is where you come in. The fastest way this changes is for enough people to know what their lights are doing and to start asking for better. The 248 of us can lay out the evidence. We cannot create the demand. Only you can do that, one informed choice at a time.

The lighting industry has known about this for years. Regulators have been slow to act. But you do not have to wait for either of them to change the light in your own home.

About the Author

Dr. Martin Moore-Ede, MD, PhD co-discovered the suprachiasmatic nucleus, the master circadian clock in the human brain, and founded the Laboratory for Circadian Physiology at Harvard Medical School. He is one of 248 scientists who contributed to the Frontiers in Photonics consensus paper on the health risks of blue-rich LED lighting. For more on the science and the campaign for healthy light, visit circadianlight.org. His book The Light Doctor: Using Visible and Invisible Light to Boost Health, Improve Sleep, and Live Longer sets out the full case.