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SAD lights, PBM & Circadian Light: What You Need to Know

SAD Lights vs Photobiomodulation vs Circadian Light

Article at a Glance: 

  • Light is an extremely powerful stimulant and tool for the human body.
  • There are several types of light therapy and lighting solutions – some of which are used for healing, whereas others may be used to support the body’s natural biological rhythms.
  • As the demand for healthy lighting options increases, SAD lights, LED light therapy devices, and circadian lighting is emerging as the next frontier in LED lighting technology.
  • Before you invest in lighting technology, it’s important to understand the difference between each of these forms of light therapy, as well as how and when to use them for maximum benefit.

Confused by all the different types of light therapy? We get it, there are a lot of options and information to unpack. In some cases, the term “light therapy” is used interchangeably for completely different products and intentions. To be clear, SAD lights, PBM, and circadian lighting are all different; they each have their own purpose. Keep reading for a deep dive on the differences between them, as well as how and when to use these devices for healthier living.

What is Seasonal Affective Disorder (SAD)?

Not to be confused with Social Anxiety Disorder, SAD is a seasonal mood disorder that often causes feelings of loneliness, depression, and/or isolation. Most cases are related to winter (aka “winter blues”) when the days are shorter, and people tend to spend more time indoors instead of absorbing natural sunlight outside. Light exposure is at the heart of this disorder.  As seasons change, people may experience a biochemical imbalance in the brain and a shift in their biological internal clock or circadian rhythm that can cause them to be out of step with their daily schedule(1). It may also cause a drop in serotonin and vitamin D levels, both of which help regulate mood(2). While not everyone with SAD experiences the same symptoms, the evidence suggests that insufficient lighting is a key culprit in triggering these symptoms.

Common Symptoms of SAD During Winter Months:

  • Feelings of hopelessness and sadness
  • Depression
  • Hypersomnia, oversleeping
  • Changes in appetite, especially craving foods that are high in carbohydrates and sugar
  • Weight gain

While rare, it is possible to experience SAD symptoms during the spring or summer too as a result of adversely getting too much sunlight. Summer SAD is similar in that it disrupts biological rhythms, but the mechanism is different. Too much light essentially turns off natural melatonin production, which your body needs in order to fall and stay asleep. Many studies have linked sleep deprivation to mood disorders, as well as obesity, heart disease, diabetes, and more(3)

Common Symptoms of SAD During Summer Months:

  • Insomnia, difficulty sleeping
  • Depression and anxiety
  • Poor appetite
  • Weight-loss(4

Recent studies indicate that SAD light therapy, also known as Bright Light Therapy (BLT), is an effective treatment option for recalibrating the body’s natural clock and alleviating SAD symptoms– particularly during winter months(5). The recommended use is 20-30 minutes per day, preferably in the mornings to mimic what you would otherwise get from natural sunlight outdoors.

Before you go and purchase a SAD light, it’s important to note that there may be a bit of a catch-22. These lamps emit light at about 10,000 lux, which is far more intense than indoor lighting, and they use LEDs that primarily emit blue wavelengths. Not all blue light is bad; however, there is a difference between signaling blue – which cues circadian responses – and toxic blue – which warps your brain and body’s perception of time.  Also, overexposure to artificial blue light has been connected to macular degeneration (over time), which is the leading cause of blindness(5). So, if you purchase a SAD light, be mindful of these things:

  • What time of day do you use the device
  • Don’t stare at the light, let it reach your skin and face without directly looking into the light
Dave Asprey Using TrueLight Energy Square Red Light Therapy Device

What is Photobiomodulation, and How Does it Work?

Photobiomodulation (PBM), also known as Low-Level Laser Therapy (LLLT) or LED light therapy, is a painless, non-invasive, and drug-free treatment that delivers light to the body for a wide range of potential health benefits. This form of therapy, which was initially developed by NASA to speed up wound healing, involves placing a light source is near or in contact with the skin, where “bioactive” light energy (photons) penetrates body tissue and stimulate the mitochondria in your cells to produce more ATP (energy). Red and near-infrared (NIR) at 660nm and 850nm, respectively, are considered the most effective wavelengths for creating this physiological reaction.  Studies show that PBM may be used to assist with:

  • Increasing blood circulation
  • Boosting lymphatic flow
  • Accelerating wound healing and tissue regeneration
  • Reducing inflammation and pain
  • Improving cellular function
  • Accelerating muscle recovery
  • And more!

PBM used to only be available in medical offices and salons, but today LED light therapy devices are more accessible and affordable, even from the comfort of home. This includes hand-held, full-body, and transportable devices to meet your personal needs. There are many ways to measure a light therapy device’s effectiveness. The best way is by how you feel when you use it, or the changes to your body you can measure. Measuring your Nitric Oxide/NO2 levels before and after use is an easy and inexpensive way to see the impact at a molecular level. But that means you must already own one. When you’re shopping, you’ll discover that there isn’t a standard way to compare your options.

You may see the “power” of a device listed, which seems like it could be a standard. However, it’s not as simple as measuring the power and ranking one with another. It’s important to take into consideration how many wavelengths the device uses, energy density, and the distance from the body that the “power” is measured.

The energy density, also known as the irradiance, that a light therapy device puts out is important. A high-power unit can make a device work faster, but more heat doesn’t necessarily mean that it’s more effective near/on the skin. In fact, PBM has a biphasic dose-responsive curve, meaning that using too much light can have negative effects and may even do nothing for you.

When a device is moved away from the surface of the skin, the power ratio goes down, so the irradiance is lower at that distance. A device may have mid-range power, so it can be comfortably used next to the skin for longer periods of time.

Note: The majority of TrueLight® LED light therapy devices fall into the ideal range of 10mw/cm2 when used at 4” to 6” away(6). The one exception here is the new TrueLight® Energy Baton Rouge®, which has a higher intensity because it covers a smaller surface area, and its timer is set to stay on for just three minutes at a time compared to larger devices which require 20-30 minutes of use. On the offhand, you only need 20-30 minutes each day to see the benefits of PBM. The key here is to be consistent about using your device – which could be anywhere from a couple of days to a couple of months, depending on what you’re trying to heal.

What is Circadian Lighting?

Given that people are spending more time indoors than ever before, there is a paradigm shift happening and an increasing demand for healthy [artificial] light sources. Circadian light, also known as human-centric light (HCL), is the next frontier of LED lighting technology.  This refers to lighting solutions that have dimming and color-tuning abilities that help align human bodies with their natural circadian rhythms — for better energy, mood, sleep, and performance.

During the daytime, it is essential to get exposure to healthy blue light, which signals important biological functions (e.g., hormones, body temperature, and sleep/wake cycle).  These wavelengths are naturally present in sunlight; however, conventional junk light – artificial light from LEDs and fluorescents — emits very intense amounts of toxic blue-violet light, which can lead to circadian rhythm disruption and other adverse health effects, including but not limited to:

  • Fatigue 
  • Eyestrain
  • Damage to the retinas
  • Social jet lag 
  • Stress and anxiety 
  • Sleep deprivation 
  • Weight gain
  • Mood disorders
  • Heart disease, diabetes
  • Cancer

At nighttime, lightbulbs that emit red light only are the most conducive for sleep. Their warmer color temperature essentially mimics what you would see while watching a sunset; this signals your body to start producing melatonin so that you can fall and stay asleep.

When shopping around for truly circadian lighting systems, keep in mind:

  • Daytime bulbs’ spectra should have a peak of 470-490nm (healthy signaling blue) range of light to promote better alertness, cognitive function, energy, and mood. There should NOT be a peak in the toxic blue-violet range (below 450nm).
  • Nighttime bulbs’ spectra should essentially emit NO blue light at all and focus on the red spectrum to simulate natural fire or candlelight.
  • The best-case scenario is to get a true day-to-night bulb that is dimmable and tunable to help keep your physical, mental, and behavioral changes that follow a daily cycle aligned with your natural 24-hour body clock.
  • Beware of painted or coated bulbs that claim to have circadian benefits.  These bulbs may appear yellow or red on the outside, for daytime and nighttime, respectively, but these LED bulbs still emit very intense levels of harmful blue light. The coatings also alter how your eyes perceive the light that it emits. The light will typically appear duller looking, and your brain will spend added energy trying to color-correct images that you see.  Unlike these bulbs that falsely claim to have health benefits, the TrueLight® Luna Red® Sunset bulb emits TRUE wavelengths of low/nonblue LED light at specific colors. It also provides a high CRI (color rendering index).  This means that the light you see emitted from our bulb allows you to see the real color of objects in your environment.  This, in turn, allows your brain to relax more – especially before bedtime — since you don’t have to over-process what you think colors should be.
  • Specifically, look for flicker-free bulbs. The flicker rate found in conventional LEDs can potentially cause eye strain, headaches, and in extreme cases, even seizures.



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