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How-to Guide
Smart Daily Light
Introduction
Humans evolved in the presence of natural daily cycles of light and darkness. Now, most of us spend the majority of the day, and time after sundown, under artificial light. We get less exposure to intense sunlight and less exposure to darkness at night. Light provides important signals for the body to function. This guide shows you how to get better light exposure while living in the modern world.
Principles
Mimic a pattern of natural light and darkness exposure across a 24-hour period.
- Adjust Behavior: Get time outside every day. You don’t need to be outside all day long. Do aim to be outdoors at least 30-60 minutes every day.
- Design Indoor Spaces: Make your indoor light more like the outside at that moment in the day. In the evening two hours before bed, only get light that is the tone of fire.
- Configure Devices: We spend a remarkable amount of our day staring at light-emitting screens. Adjust device settings to make the light emitted more appropriate for the time of day.
Light Types
All the different light types below have important effects on our physiology.
- Visible Light: We see light with a wavelength of about 400-700 nanometers (nm). Visible light is important for vision and the synchronization of our bodies’ clocks with the natural light and dark cycle of a 24-hour day. This synchonization affects alertness, mood, blood pressure, immune function, vision, and much more.
- Ultraviolet (UV) Light: This type of light, shorter in wavelength than visible light, is categorized into UV-A (320-400 nm), UV-B (290-320 nm), UV-C (200-280 nm), and UV-V (100-200 nm). Exposure to UV-B radiation leads to vitamin D synthesis and nitric oxide synthesis in the skin. Vitamin D is involved in numerous biological processes, including bone mineralization and immune function. Nitric oxide relaxes blood vessels helping to deliver blood throughout the body and to lower blood pressure.
- Red and near-infrared light: The type of light ranges from just inside the visible spectrum with red light (660-700 nm) to outside of what the eye can see with near-infrared light (700-1400 nm). Light in this spectrum can penetrate the skin, and among other things, may improve how efficiently mitochondria produce ATP – the energy currency of our cells.
- Darkness: Yes, the absence of visible light is also important for the human body. Environmental darkness translates into higher levels of the hormone melatonin, which signals to the body that it is dark outside. Melatonin takes part in various nighttime activities and functions including sleep induction and maintenance, antioxidation throughout the body, blood sugar control during your overnight fast, repair of DNA damage, and more.
- Virtual Darkness: When certain wavelengths in the visible spectrum, especially light in the blue-cyan wavelength (400-490 nm), but to a lesser extend the green-cyan spectrum (400-560 nm) are absent or blocked from entering into the eye (like with blue blocking glasses, for example), you can create “virtual darkness”. Your visual system can see but your circadian system is not being told it’s daytime. We can take advantage of in the evening to create a more natural light signal to the body.
Light Intensity and Temperature
Intensity
The intensity of light denotes measures of the total quantity of visible light emitted by a source per unit of time. The more photons of light emitted per second, the more intense that light source is. This can be measured in various units including lux, lumens, or candela. One lux is one lumen per square meter. One candela is the luminous intensity of one candle. Here is why this is important to know: Even though you can see perfectly fine in a well-lit room, outdoor daytime light at noon on a clear sky day is orders of magnitude more intense than bright room light. Therefore, there is a much stronger signal of daytime to the brain from sunlight than from a room well-lit with artificial light.
Temperature
The color or temperature of visible light is measured in the unit Kelvin. The color temperature of natural light changes across the day.
Measuring Light to Get It Right
A light meter is useful to assess your lighting environments
- Daytime light recommendations for indoor environments:
- 250 lux or more
- Make the light cooler in color temperature.
- Evening light recommendations for residential and other indoor environments:
- 10 lux or less
- Starting at 2-3 hours before bedtime
- Make the light warmer in color temperature.
- Nighttime light recommendations for the sleep environment:
- The sleep environment should be as dark as possible.
- The recommended maximum ambient melanopic EDI is 1 lux measured at the eye.
- During activities at night that require vision, aim to use light no stronger than 10 lux.
- Use amber or red light only.
The MT-912 Light Meter by Urceri
Illuminance measuring range: 0 - 200k Lux
Please note, that this device is measuring temperature, but it’s not color temperature. It’s actual temperature, which is valuable for photographer but not for our purposes here. The main value here for you is the measurement of light intensity.
Lighting Strategies
Confirgure indoor light and screens that matches with ;outdoor light at that particular time of day.
Morning Light
- 10 minutes outside before 10a (or within a few hours of waking): 10min before 10a is a heuristic that makes the idea easier to remember. Go for a walk, read the news, or have your coffee or tea under outdoor morning light. Doing so will improve sleep on the night you do this.
- Bright light therapy: If you live in a region where there is little daylight during the winter, consider using a bright light therapy lamp within three hours of waking. The Luminette 3 device is a very convenient options that allows you to do about your morning, making breakfast, reading news, etc, while wearing this headset device. Strategies like these are especially useful for people with seasonal affective disorder.
Midday Light
- 30-60 minutes outside daily: Spend at least 30-60 minutes outdoors during daylight each day: This is typically easy to accomplish during non-work days, but it can be tricky on work days. To get around this, try the following:
- Commute: Walk, ride a bike, or scooter for all or at least part of your commute.
- Lunch: Spend your lunch break outdoors.
- Meetings: Take walking meetings or simply sit outside.
- Windows: Sit near windows during daylight hours when you can.
Evening and Night Light
- Evening Lighting:
- Dim the intensity all artificial light sources.
- Use warmer color temperature bulbs or filter out the blue light from all light sources by wearing blue-filtering glasses:
- Night Lighting: Sleep in darkness. Any light emitted from clocks or other electronics should be deep amber or red light only. Before bed ensure your path to the bathroom is unimpeded at night. And when going to the bathroom or engaging in other activities, use as little light as is necessary, being particularly careful to avoid exposure to blue light. Sleep in darkness and block white light from alarm clocks and other sources. Light can penetrate closed eyelids and affect your body clock timing.
LED Light Blocking Stickers from Jieheng
Take the right sized sticker and put it over the light-emitting electronic. The nice thing about these stickers is that then dramatically dim the light but you can also still see that the device is on and working. Sometimes, you might need to use two of these stickers on top of each other if the light is particularly bright.
- Shift your body clock earlier: If you usually wake to an alarm clock and want to fall asleep earlier, increase your exposure to light in the first three hours after waking by spending time in daylight or using bright light therapy. Then, be diligent about reducing your light exposure in the three hours before your planned bedtime. This is especially relevant to teenagers who must wake up early for school because their biology makes them way to stay up later and wake up later which causes friction with school schedules.
- Shift your body clock later: If you go to bed and wake very early, reduce your exposure to light in the first three hours after waking by wearing blue-blocking glasses (or sunglasses if outdoors). This is especially relevant to elderly people who are prone to waking up very early.
See our How-to Guide on reducing jet lag for more details on how to shift your body-clock timing.
Light Solutions
Bulbs
- Turn off lights: In the evening after sundown, turn off unnecessary lights that you are not using in your home. Turn off lights in rooms that you are not in and look to have only one light on in the room you’re in.
- Dimmers: Ideally, all lights in your home have dimmer switches so you can lessen the intensity of any light you have on. As your evening advances from earlier to later, progressively dim your lights so that they are very dim 90 minutes before bed until you turn the lights off.
- Daytime Lamps, Nighttime Lamps: One excellent strategy is to use different lamps for different times of day. Here is an example scenario. In John’s bedroom, he has lamps he only uses in the morning and during the day. These lamps have LED bulbs that emit full-spectrum white light ranging in temperature from 4000-6500 kelvin. On his bedside table, however, he has other lamps he only uses in the evening and before bed. These lamps have LED bulbs that emit warm tones of light ranging from 3500 kelvin or lower. You can replicate this example scenario throughout your home.
- Bulbs that change color and intensity: The most sophisticated and best option is to have lamps that can have the temperature of color change according to the time of day. Those types of bulbs are now widely available and can usually be controlled with smartphone apps that pair with the bulbs. They can also integrate with voice control services (eg., Amazon, Google, Apple) so that you can program or tell your lights to be a certain tone and intensity at a certain time of day.
New lighting technology allows you to change the color of the light from an app. Other types of new bulbs are cooler in temperature at full brightness and then warmer in temperature as they are dimmed. Many people, however, face having to choose one temperature light for their homes. If that is your situation, what temperature lights should you choose to buy? Many people are outside of their homes during the day and are at home using indoor light in the morning before work and in the evening after work. If you have to choose one temperature bulb, go with a warmer bulb around 3000-3500 Kelvin. It is a compromise that prioritizes warmer light in the evening which is better for the circadian system.
Color rendering describes how a light source affects the appearance of an object's color to the human eye and its ability to reveal subtle color variations. The Color Rendering Index (CRI) measures this capability on a scale from 0 to 100 percent, comparing the light source to a standard reference. Higher CRI values indicate better color rendering: a CRI of 85 to 90 is considered good, while 90 or higher is excellent, ideal for tasks requiring precise color discrimination.
Note that CRI is independent of color temperature. For example, a 2700K incandescent light has a CRI of 100, whereas two 5000K fluorescent lights can have CRIs of 75 and 90, respectively.
Blue-Filtering Strategies
Regardless of what bulb strategy you choose to go with above, consider adopting some of these other blue-filtering strategies, as well. Interestingly, fully blocking blue light in the evening is very pleasant for the eyes but it’s not necessarily pleasant for our visual system, which prefers images with a full spectrum of color. Do your best and know that some blue filtering is better than none at all.
- Glasses: Blue filtering glasses can range in how much blue they actually filter (i.e., transmittance). You can use lower-filtering glasses earlier in the evening and higher-filtering glasses starting 90 minutes before bed until you turn the lights out for sleep.
- Gels: Gels are plastic films that photographers use on their work sets. We recommend that everybody gets one set of red gels - that you can cut into smaller pieces - to put over any light-emitting device, like a bedside clock, that emits white light. They’re also great to bring with you when traveling to put over clocks and other light sources that won’t turn off while you were trying to sleep.
- Software: F.lux is a software program that you can install on your computer that automatically detects the time of day and starts to filter out the blue light as the sun goes down. It will continue to increase the amount of blue pulled out from your monitor as it gets closer to your bedtime. Independent of this software adjusting the temperature of your screen, you should also reduce the brightness of your screen manually.
- Travel Ideas: Purchase amber-toned or red-toned string LED lights. Store them in large Ziploc bags and bring them with you while traveling. Keep one set of string lights for the main room and one set for the bathroom for your hotel room. Use these lights, and these lights only, 90 minutes before bed.
- Device Settings: Users of Apple iPhones can use “Night Shift” mode, which enables you to filter some blue light from your iPhone or iPad at night. However, altering the color tint of the screen allows you to filter even more blue light from your screen to create an even better dark mode for these devices.
For Android Users, see below for the product called Twilight
First, you’ll adjust the settings for Color Tint , then you’ll set a trigger so that you can easily turn it on and off.
Set Up Color Tint
Step 1: Set the color tint
- Settings app → Accessibility → Display & Text Size
- Enable ‘Color Filters’
- Set Intensity to Maximum
- Slide Intensity all the way to the right
- Slide Hue all the way to the left.
Step 2: Set the trigger
- Settings app → Accessibility → Scroll to the bottom of the page.
- Set “Color Filters” to on.
Step 3: Add Color Tint to Accessibility Shortcuts
- Settings app → Accessibility → Accessibility Shortcuts:
- Check “Color Filters” in menu of items.
Step 4: Set up Control Center
- Settings → Control Center → Customize Controls.
- Add “Accessibility Shortcuts” to control center.
Activating Color Tint on Your Phone
Step 1: Open Control Center
- First Way:
- Slide your finger down from the upper right of your screen.
- Click “Acccessibility Shortcuts.”
- Click “Color Filters” on or off.
- Second Way:
- Tripple click right side button on phone.
- Click “Color Filters” on or off.
Related Resources
Light Measurement
- Urceri Light Meter: This device measures light strength from 0 to 200,000 Lux and ambient temperature with a high accuracy. A useful device to test whether the light in your spaces is suitable for the time of day.
Smart Lighting
- LIFX: Using a LIFX smart lighting system, you can wirelessly tune your indoor lighting to your exact preferences using the associated app, voice assistants (e.g., Amazon Alexa), and other smart home technologies. LIFX bulbs are easy to use and don't require a hub, and we find the user experience intuitive.
Light Therapies
- Verilux: If you struggle with a seasonal affective disorder or simply seek intense indoor lighting because you cannot spend much time outside during daylight, some light therapy devices emit 10,000 lux of light, which is far stronger light than typical room lighting.
- Luminette 3: A portable, wearable headset that allows uers to enjoy light therapy sessions anywhere, even while exercising, traveling, or working. The Luminette 3 emits a blue-enriched white LED light at 3 different intensities (500, 1000, and 1500 lux) that have been clinically proven to effectively treat winter blues and improve sleep schedules. An independent clinical trial demonstrated the Luminette device provides equivalent benefits to a traditional light therapy box. Each charge lasts for 5-10 light therapy sessions. They are compatible with contact lenses and glasses, making them easy to use.
- Lumus.tech: This sleep mask pulses perfectly timed light into your eyes while you sleep to shift your body clock while you sleep so that you can adjust to a new timezone more quickly while traveling. You can learn more about this mask and the technology behind it in Dan’s podcast conversation with Professor Jamie Zietzer from Stanford
Travel String Lights
- Novelty lights (Amber, Red ): These lights emit a gentle amber or red light (depending on the type you get) that provide enough light to see at night without being alerting and while having a minimal effect on shifting your circadian rhythm.
Alarm Clocks
- Sunrise Alarm Clock by LaBell: This relatively inexpensive alarm clock has many useful features, including simulated sunset and sunrise, multiple alarms, and more.
- Sleep and Wake-up Light Therapy Lamp by Phillips: This alarm clock has a host of useful features, including simulated sunset and sunrise, a breathing tool to help you fall asleep faster, and much more.
Blue-Blocking Glasses
Light-Covering Gels
Eye Masks
Blackout Blinds
Apps
- F.lux (for macOS and Windows). When the sun is down wherever you are, f.lux gives your laptop or PC screen a reddish hue, which should reduce the negative effects of light exposure from your computer at night on your body’s clock and sleep.
- Twilight (for Android phones only). This does much the same thing for Android phones as f.lux does for computers. (iPhone users can enable Night Shift mode for similar effects.
TEDx Talk
- How to Optimize Light for Health - by Dan Pardi, MS, PhD