Dr. Andrew Huberman, Ph.D. is a Professor of Neurobiology and Ophthalmology at Stanford University School of Medicine. His lab focuses on neural regeneration, neuroplasticity, and brain states such as stress, focus, fear, and optimal performance.
In this episode, Andrew Huberman describes the mechanisms by which different wavelengths of light impact the cells, tissues, and organs of the human body, and how specifically timed light exposure of specific wavelengths can be used to improve sleep, and enhance alertness, modulate hormone levels, and improve mood.
Host: Andrew Huberman (@hubermanlab)
Light is electromagnetic energy
Light travels in many different wavelengths and affects the brain, body, environment, etc.
There are wavelengths of light that are not visible to the human eye (e.g., UV light)
Light impacts us at different levels, i.e., wavelengths
Different wavelengths of light can penetrate tissues to different depths
Shortwave light (e.g., blue, green, UV light): doesn’t penetrate tissue easily beyond the top surface of the skin
Longwave light (e.g., red): can penetrate way beyond the top layer of tissue and maybe even down to bone or bone marrow
Time of exposure to different types of light can change the way the cells and organs of the bodywork
Every cell in the body will have an altered function (for better or worse) when accessed by light
The impact of light on the body is uniquely important – more so than drugs, sounds, food, touch, anything: particular wavelengths of light can be used to stimulate the function of particular organelles within particular cells within particular organs of the body
Absorption of light energy: certain pigments in object receiving the light energy are going to absorb particular wavelengths of light
Absorbance properties of surface receiving the light indicative of whether light penetrates or bounces off
Rods in the eye are used to see in low light conditions
Cones in the eye see color (baring colorblindness) and can absorb different wavelengths
Surprisingly, rods and cones demand the most energy out of all the cells in the body
Skin pigment melanocytes absorb UV light and create changes in skin pigmentation
A calorie is essentially food’s light energy: the heat at which a certain food burn gives you a sense of how much energy it can provide your body (i.e., calories)
Impact of light can be direct (e.g., light onto skin or photoreceptors in the eye) or indirect (e.g., light hits photoreceptors then starts a domino effect to downstream organ or cell) – but all starts with a particular wavelength of light being absorbed
Example of the rapid effect of light on the body: if you go into a bright room or are exposed to bright light shortly after waking, it mimics the wake-up effect similar to that of being dunked in very cold water
The body takes in information about light and slowly changes the way biology works
Even one exposure to UVB light changes hormones release
On longer days or in bright light environments, we tolerate pain (nociception) better
Circannual rhythm: rhythms that exist within the body and hormone release throughout the day and night as an indicator of where you are in the 365-day calendar
The light activates cells which shut down the production of melatonin
  • On short days: melatonin release is longer
  • On longer days: melatonin release is shorter
On average, melatonin is an indicator of how much light is in the environment
Endogenous melatonin has two categories of effects: (1) regulatory effects; (2) protective effects
Regulatory effects of melatonin: positively impact bone mass by the production of osteoblasts, maturation of gonads and ovaries, effects on the central nervous system in terms of waking up or making us sleepy  
Protective effects of melatonin: activate the immune system, potent antioxidant properties
It’s critical to get the proper amount of sunlight to our eyes each day
Light powerfully inhibits melatonin – but our bodies are accustomed to the natural changes in melatonin in relation to the natural calendar rhythms
Avoid melatonin supplementation! Try other approaches to regulating sleep before consuming over the counter melatonin because the amount in the supplement is several times our natural, endogenous level
Melatonin inhibits testosterone and estrogen output from the testes and ovaries which is critical to the desire to mate
Skin is a hormone-producing and hormone influencing organ: skin exposure to shortwave light (e.g., blue, UV) can trigger increases in testosterone and estrogen and the desire to mate
People from places with lower light throughout the year or lighter skin experience more significant increases in testosterone with light exposure
Seasonal effects of testosterone: testosterone levels appear lowest in the winter months and highest in June, July, August, September
Our bodies are better at combating infection during the summer & spring months because the increased UVB light enhances spleen function
Getting as much UVB light in the eyes and on the skin early in the day is critical to sleep, wakefulness, and mood
Bright light at the wrong time in the 24-hour cycle can make your mood worse: dopamine output drops, “happy hormones” reduce output
UV exposure in the morning and day is important but avoiding light exposure at night is equally critical
Avoid shortwave light (blue, UV) exposure between 10 pm and 4 am – or even 8 pm onward if you suffer from depression
Even just one night of dim light exposure during sleep (even if it doesn’t wake you up) may impair cardiometabolic function such as increased insulin resistance and decreased heart rate variability
During a night of healthy, deep sleep our body transitions through various forms of metabolic function – disruption will affect cardiac function and metabolic light
Redlight therapy & LLT can improve acne and skin lesions by penetrating through the skin and triggering certain biological pathways in a deeper layer which replace damaged skin
Light activation drives pathways that either stimulate the death of cells or stimulation of healthy cells that restore youthfulness
Important note: LLT for skincare treatments should be hot enough to penetrate the skin but not burn it; therapy should also be targeted and illuminate only patches seeking repair
The ability to keep retinal neurons healthy is extremely important – we don’t generate more neurons throughout life
Red light may reverse age-related vision loss: exposure to red light within three hours of walking, at a safe distance for a few minutes each day may improve visual acuity and function, particularly rescuing the function of rods and cones
Tip for shift workers or people awake at night for childcare, etc.: if you need to be awake at night, red light is the best choice because it will not inhibit melatonin or increase cortisol
The exciting potential of wavelength brain stimulation: a pattern of flashing light delivered to the eyes creates a pattern of neuronal firing that triggers molecular which reduce markers and the causes of age-related decline in the brain – and – up-regulation of biological pathways that lead to enhancement of neuronal function
Skin exposure to UVB light induces a skin-brain-gonad axis and sexual behavior (Cell Reports)
Skin Exposure to Ultraviolet B Rapidly Activates Systemic Neuroendocrine and Immunosuppressive Response (Photochemistry and Photobiology)
A visual circuit related to the periaqueductal gray area for the antinociceptive effects of bright light treatment (Neuron)
Light exposure during sleep impairs cardiometabolic function (Proceedings of the National Academy of Sciences)
Light-emitting diodes in dermatology: A systematic review of randomized controlled trials (Lasers in Surgery and Medicine)
Low-level laser (light) therapy (LLLT) in skin: stimulating, healing, restoring (Seminars in Cutaneous Medicine and Surgery)
Weeklong improved colour contrasts sensitivity after single 670 nm exposures associated with enhanced mitochondrial function (Scientific Reports)
Red light: A novel, non-pharmacological intervention to promote alertness in shift workers (Journal of Safety Research)
Gamma Entrainment Binds Higher-Order Brain Regions and Offers Neuroprotection (Neuron)