By now, we all know light plays a significant role in our daily lives, controlling everything from physiology to mood! You've likely heard that getting sunlight first thing each morning is one of the most essential parts of a daily wellness routine, along with drinking water upon waking and forgoing bright blue lights in the evening.

But why is it so essential for us to get some light first thing each day? 

The answer has to do with the effects of light on our circadian rhythm. 

Today, let's dive deeper into this all-encompassing daily biological rhythm that keeps our health and lives running like clockwork. 😉

What is the circadian rhythm?

The circadian rhythm is the body's internal clock that operates on a 24-hour cycle and controls/times various biological processes: everything from our sleep and wake schedule, hormones, digestion, body temperature, and more.

Synchronized with our environment by a part of our brain's hypothalamus called the suprachiasmatic nucleus (SCN), the SCN acts as our internal timekeeper and is most influenced by signals from our eyes by the presence of light in our surroundings. (Other signals, like the timing of meals, also exist but are considered secondary signals). 

You likely intuitively understand your own personal circadian rhythm: if you wake up, sleep, and get hungry at the same time every day, that's a prime example of your personal circadian rhythm at play! 

How does light affect sleep and the circadian rhythm? 

The short answer: through the interaction of light (especially blue light!) with the eyes and brain, and the hormones melatonin and cortisol!  

The Eyes:

Apart from the rods and cones (image-forming photoreceptors in the retina of the eye that allow us to see), we also have specialized non-image-forming photoreceptors called melanopsin retinal ganglion cells that are responsible for our circadian entrainment, conveying information from our external environment to the brain's suprachiasmatic nuclei (SCN), or our brain's "master clock".

When light enters the eyes, a signal is sent to the SCN, which tells the pineal gland to suppress the secretion of melatonin. 

Visible Light: 

As we've just seen, visible white light and its constituent blue light wavelengths are the main timekeepers for the circadian rhythm. 

Activated by the presence of light, our melanopsin-containing retinal ganglion cells send signals to the brain to keep cortisol levels high during the day to promote alertness and wakefulness while suppressing the secretion of  melatonin, the hormone best known to induce sleepiness.  

While all wavelengths of light can activate this signaling system, our retinal ganglion cells and the photopigment melanopsin are primarily activated by shorter wavelengths of light, with peak absorption at around 480nm (blue light)! These wavelengths of light are present in high amounts in natural sunlight during the morning and daytime and in artificial light of a color temperature above 4000K.

While blue light wavelengths are the primary suppression signal for melatonin, if bright enough, any light can suppress melatonin secretion (even red light)!

Melatonin + Cortisol: 

Melatonin and cortisol are two hormones that release on opposing rhythms and are the primary chemical mediators providing the signals that set our internal clocks (among all their other roles!)

For this limited scope of discussion, melatonin initiates the inactive phase and increases our drive to sleep, while cortisol begins the active phase and increases alertness and wakefulness. 

Ideally, melatonin rises at night, peaking around 2 - 3 am. Melatonin will then drop with the onset of environmental light and remain low throughout the day, while cortisol will be raised in its stead, working to keep us motivated and alert.

Lighting Tips for Morning and Daytime 

Use bright white light

Aim for at least 20 - 30 minutes of daylight exposure upon waking each day (without sunglasses for optimal exposure). 

Remember, the presence of bright light signals to the brain to suppress the release of melatonin, releasing cortisol in its stead. Getting plenty of sunlight (and constituent blue light) in the morning enables our master clock to "reset" and understand this is the wakeful period.

- Open all window blinds + turn on overhead lights upon waking. Opt for light with color temperatures around 3750/4000K or above (natural white, cool white, or daylight white will work!) This R30 is our favorite for 4 or 5" recessed cans.  

- Get outside! Take a morning walk or have your morning coffee on the porch.

- Use a light therapy device to help on rainy days and during the winter. 

Lighting tips for a good night's sleep 

Use only dim, warm color temperature light

Minimize or eliminate sources of white light in the evening (device screens, overhead white lights, etc.) Keep the brightness of all light at a minimum. Any light, if bright enough, can keep you up!  

- Dim overhead lights or turn them off altogether

While a lot of attention rests on light color, brightness can be equally as important. Too bright a light triggers your pupillary reflex, which tells your brain that it's time to wake up! 

Turn off any overhead lights and use desk and floor lamps outfitted with warm white light bulbs instead. 

-Use warmer color temperature lighting in the evening

Remember that a light's color temperature can give us a clue to which color its spectrum skews more towards - blue (energetic light that is awakening), or red (soothing light that won't suppress melatonin - the sleep hormone).

We recommend using desk and floor lamps outfitted with warm white light bulbs ( anything 2700K-3500K ) or, our personal favorite - the Chromalux® 60W frosted bulb).

- Use blue light filters on devices (set screen color temperature to warm)

If you'll be using devices, set screens to a warmer color temperature using an app like f.lux or your operating system display settings. Ideally, screens should be amber or red and very dim.   

In summary, remember the following for a healthy circadian rhythm:

- Go to sleep and wake up at around the same time each day. 
- Get some sun every morning! Your overhead lights during the morning and daytime should be bright and preferably more "white" in color temperature (anywhere from 4200K-6500K).
- Set a relaxing bedtime ritual and stick to it.
- Follow the above guidelines on limiting screen time, turning on screen filters, wearing blue light blocking glasses, and dimming lights. In addition, all lights should be of a warmer color temperature in the evening (around 2700K-3500K), very dim, and optimally only used in floor or table lamps (no lighting overhead).

Best light bulbs for sleep

This article wouldn't be complete without a list of some of our favorite light bulbs for sleep! The following are some of our favorite light bulbs by Chromalux®. 

Remember, the best light color to help you sleep is anything "warm" - whether that means warm white (for LED bulbs), or any other technology of bulb that has a color temperature below 3700K or so. 

Take incandescent light bulbs for example: they are naturally warmer in color temperature and therefore skew more towards the red color in their spectrum - making them the perfect candidate for nighttime usage! Unique to Chromalux® incandescents are their special glass that enhances colors and contrast, so nighttime reading becomes even easier! 

Our favorite night time bulbs, then: 

For overhead recessed lighting: Chromalux® R25 60W flood bulb

For bedside table lamps: Chromalux® B10 medium base 25W, or Chromalux® A19 60W frosted 

💡Thanks for reading!

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