Winter brings shorter days and less sunlight, leading many people to notice changes in their mood and energy.
As a medical student in the late 1980s, I researched seasonal affective disorder (SAD) during my psychiatry rotation. I’ve followed the science of light therapy for nearly 40 years, watching it grow from an incipient treatment to a standard medical intervention offered through light therapy lamps.
How Light Therapy Lamps Work in Your Body
Our bodies run on internal clocks called our circadian rhythm. Almost every protein and bodily function follows precise timing, including our emotional state and energy levels.
When days grow shorter, with later sunrises and earlier sunsets, we get less morning light to start our day. Many people feel they never fully “wake up,” experiencing decreased mood and energy from living out of sync with their circadian rhythm.
SAD’s medical definition includes a seasonal pattern of fatigue, oversleeping, weight gain, decreased mood, and reduced interest in activities. The condition affects between 0.5% and 10% of people, depending on latitude — from 1% in Florida to 9% in Alaska. However, many more people experience milder symptoms during darker months without meeting the full diagnostic criteria.
Understanding Light and Your Body Clock
Scientists use the German word “zeitgeber” (meaning “time giver”) to describe the environmental cues that reset our internal clock. Light is the strongest zeitgeber, reaching us primarily through our eyes.
Our eyes process light through several pathways. The retina contains rods (for black and white vision in low light) and cones (for color vision in bright light). We also have specialized non-visual cells called intrinsically photosensitive retinal ganglion cells (ipRGCs). These cells contain melanopsin, a molecule sensitive to blue light at 480 nanometers, and they send signals directly to our brain’s master clock: the suprachiasmatic nucleus.
Source: The Evolution of Light Therapy Lamps
Traditional light therapy lamps have proven effective at resetting our circadian rhythm, reducing SAD symptoms by 40%–60%. The standard approach involves sitting in front of a light therapy lamp that produces 10,000 lux of whitish-blue light first thing in the morning.
To put the brightness of a light therapy lamp into perspective:
- A typical indoor light bulb produces about 150 lux.
- A cloudy day outdoors reaches around 1,000 lux.
- Direct sunlight at noon can hit 100,000 lux.
- A standard light therapy lamp delivers 10,000 lux (it is a bright light!).
The Science of Sunrise and Sunset
Research from the University of Washington uncovered another way light affects our internal clock.
We have three types of cone cells:
- S cones detect blue light.
- M cones detect green light.
- L cones detect red light.
These researchers discovered that our cones respond to specific blue-yellow color contrasts occurring at sunrise and sunset. This second pathway helps regulate our internal clock independently of the melanopsin system. This makes sense from an evolutionary point of view. Our ancestors watched sunrises and sunsets, naturally synchronizing their circadian rhythms with their environment.
Beyond Traditional Light Therapy Lamps
This understanding led to the TUO light bulb.
Unlike traditional light therapy lamps that require dedicated morning sessions, this smart bulb cycles through sunrise and sunset colors at speeds too fast for conscious perception. While appearing as white light, it creates the exact color combinations that help synchronize our internal clock — and does so at just a few hundred lux instead of the intense 10,000 lux of standard light therapy lamps.
Image Credit: The TUO Life
The TUO system includes:
- Wi-Fi-enabled bulbs (about $50 each)
- Smartphone app for custom timing
- Three light modes:
- Wake mode for morning activation
- Calm mode with reduced blue light for evenings
- Neutral mode for midday
While randomized controlled trials haven’t yet confirmed the TUO bulb’s effectiveness for SAD (the technology is too new), the underlying science suggests it should work.
While traditional light therapy lamps remain effective for SAD treatment, new technologies offer different approaches. Standard light therapy lamps deliver intense light in focused sessions, while newer smart bulbs like TUO provide gentler, timed light exposure throughout the day.
Beyond SAD: Social Jet Lag
SAD affects a small portion of people during specific seasons. But “social jet lag” impacts most of us year-round.
Before the advent of artificial lighting, humans woke with the sun and slept after sunset. This pattern matched our evolved biology. Today, few city dwellers follow these natural rhythms.
Living out of sync with our internal clock impairs both our emotional and physical health. New lighting technology lets us create artificial sunrises and sunsets indoors, helping restore natural patterns even in modern life.
Setting Up Your Light Therapy System
I use these new light therapy bulbs in my own home. Most people have a “delayed phase” sleep pattern — their internal clock runs longer than 24 hours, making morning wake-up difficult. These people benefit most from morning exposure to a light therapy lamp or smart bulb system.
For optimal results with TUO bulbs, place them where you spend time in the morning:
- Bedroom
- Bathroom
- Kitchen
The latest smart bulbs can automatically adjust throughout the day, providing energizing light in the morning and reducing blue light before bed. They’re more convenient than traditional light boxes while working with our body’s natural light-sensing mechanisms.
Talk with your doctor about whether light therapy makes sense for your situation. With proper timing and implementation, it can restore your body’s natural rhythm and improve your mood and energy not only during the darker months but throughout the year.
