Sleep is vital for overall health and wellbeing. Getting an adequate amount of high-quality sleep each night can help improve concentration, productivity, mood, and immune function. Many people have trouble falling asleep and staying asleep throughout the night. Researchers have been studying how different types of light, especially from electronic devices and overhead lighting, can impact the body’s internal clock and disrupt normal sleep patterns. Recently, there has been interest in using LED light bulbs that emit purple wavelengths to possibly promote better sleep.
What is purple LED light?
LED stands for light-emitting diode. LED light bulbs are energy efficient alternatives to traditional incandescent bulbs. They work by passing electricity through a semiconductor material, which emits light. The color of light that an LED bulb produces depends on the composition of the semiconductor material used inside the bulb. By using different combinations of certain elements, LEDs can be manufactured to give off different colors on the visible light spectrum.
Purple LED light bulbs have an emission peak somewhere within the purple or violet wavelengths, which range from about 380-450 nanometers. Some purple LED bulbs have a narrow emission centered around 420 nm. Other versions have a broader span of wavelengths in the purple-blue spectrum. Compared to standard white LEDs that emit a broad band of blue, green, and red wavelengths, purple LEDs have a more focused spectrum.
How does light impact sleep?
Light is the strongest external factor that influences circadian rhythms. These intrinsic 24-hour cycles govern many biological processes including the sleep-wake cycle. Circadian rhythms are regulated by an internal biological master clock located in an area of the brain called the suprachiasmatic nucleus. Light signals received through the eyes are the primary way that this master clock synchronizes to the external day-night cycle.
During the day, exposure to light suppresses production of the hormone melatonin and helps maintain alertness. At night, darkness triggers the release of melatonin, which induces drowsiness and facilitates sleep. Blue wavelengths around 460-480 nm seem to be the most potent for suppressing melatonin. Too much blue light exposure in the evening from phones, tablets, and overhead lighting can make it harder to fall asleep and reduce sleep quality.
How do different wavelengths impact sleep?
Wavelengths in the blue-green range have the biggest impact on sleep. Here is a summary of how different parts of the visible spectrum influence sleep:
| Wavelength range | Effects on sleep |
|---|---|
| Blue (450-495 nm) | Strongest suppression of melatonin, can delay circadian rhythm and disrupt sleep |
| Green (495-570 nm) | Some melatonin suppression, but not as potent as blue light |
| Yellow (570-590 nm) | Minimal impact on sleep |
| Orange (590-620 nm) | Minimal impact on sleep |
| Red (620-750 nm) | Low melatonin suppression, less sleep disruption |
Some research indicates that longer wavelengths like amber and red light have less of a sleep-disrupting effect in the evening and might even help promote sleepiness compared to blue light. There is also interest in purplish-blue wavelengths between 446-477 nm that fall between the peaks for melanopsin retinal ganglion cell stimulation (around 480 nm) and melatonin suppression (around 460 nm). Early studies have found reduced melatonin suppression from narrow-band purple/violet LED light compared to blue LEDs with similar brightness.
Does purple LED light improve sleep quality?
Several small studies have specifically investigated how exposure to purple LED light in the evening impacts sleep quality compared to blue, green, and red wavelength LEDs. Overall, they suggest that purple LED light bulbs may help create a more sleep-conducive environment at night compared to standard white or blue-enriched LEDs.
In an experiment published in Clocks & Sleep in 2020, researchers had 17 healthy adults use different LED light bulbs with peak wavelengths of 469 nm (blue), 516 nm (green), and 630 nm (red) for 3 hours before bedtime. The 630 nm red LED light increased melatonin levels at night compared to blue and green light. In a follow-up study in 2021, the same researchers tested a 420 nm purple LED in 13 healthy young adults. Using the purple LED for 3 hours before bed helped increase sleep quality and duration compared to the blue LED light.
Another study in the Journal of Physiological Anthropology in 2019 tested 470 nm blue LEDs, 520 nm green LEDs, and two different near-purple LEDs peaking at 420 nm and 440 nm in 10 healthy men. The 420 nm purple LED light increased melatonin levels at night and decreased levels of alertness before bed compared to blue and green LEDs. The researchers concluded the 420 nm purple light was significantly less likely to disrupt circadian physiology.
However, not all studies have found major differences between purple light and other wavelengths. A 2018 study in Neuroscience Letters had participants use short wavelength 437 nm purplish-blue LEDs, medium wavelength 516 nm green LEDs, and long wavelength 633 nm red LEDs at night. While the red LED light increased melatonin levels, the researchers did not find significant differences between purple and green LEDs in terms of melatonin, sleepiness, or sleep quality measurements.
More controlled human clinical studies with larger sample sizes are still needed. But overall, initial findings suggest that purple LED lighting may be a safer alternative to blue-rich lighting at night for people who are prone to sleep disturbances. Using purple LED bulbs in the hours leading up to bed in places like the bedroom, bathroom, and living areas may create a more circadian-friendly evening lighting environment.
Should I use smart light bulbs?
To optimize the sleep benefits, most experts recommend using a smart LED lighting system programmed to automatically change color and brightness depending on the time of day. Here are some reasons why smart LED light bulbs can be helpful for improving sleep:
- They can be scheduled to emit brighter, bluer light in the morning and early afternoon to boost alertness and concentration.
- The light can gradually fade to dimmer, warmer, and purplish hues as evening approaches to help the mind and body relax before bed.
- Many smart lights can be controlled remotely via smartphone or voice assistant when you are away from home so you can customize the lighting to match your sleep schedule.
- Some systems allow you to program a customized circadian rhythm lighting schedule tailored to your individual chronotype and sleep-wake times.
Look for smart LED bulbs and panels that allow tuning of correlated color temperature and provide shades in the warmer white, amber, red, and purple spectrum. The best circadian-friendly smart lights will have an option for programming a scheduled automatic circadian rhythm cycle.
Potential risks of purple LED lights
While more research is still needed, purple LED lighting appears safer for nighttime use than standard cool white or blue-enriched lighting when used properly. However, there are some potential downsides to be aware of:
- Purple LEDs could potentially cause eye strain, headaches, or other adverse effects when used for extended periods in the evening, especially at close distance. But these effects will likely be much less than blue wavelengths.
- Not all purple LED bulbs are suitable for general indoor lighting. Deep ultraviolet LEDs may be unsafe. Use products from reputable lighting brands that are designed specifically as white/color tuning bulbs for home use.
- Bright light of any color temperature can be activating. So avoid using intensely bright purple lights before bedtime. Dimmer output is better for sleep.
- Purple shades like lavender and orchid may be relaxing, but deep violet light is still more stimulating for the circadian system than warmer amber and red wavelengths.
The short-wavelength light from purple LEDs is still able to suppress melatonin at some level and impact sleep-wake cycles, especially at high intensities. But most people can likely tolerate moderate use of purple light in the evening better compared to blue light exposure. Those with high light sensitivity may still choose to use orange or red lighting at night.
Tips for using purple LED lights for better sleep
Here are some tips to use purple LED lights optimally to improve sleep quality:
- Install purple smart bulbs in table lamps, floor lamps, and overhead bedroom lighting to control the ambiance during evening hours.
- Set lights to gradually dim and shift purple/pink during the 1-2 hours before bedtime.
- Avoid using purple lights at full brightness close to bedtime. Keep bedroom lighting quite dim.
- If using electronic devices at night, install purple light filters to block blue wavelengths.
- Pair purple evening bulbs with a sunlight lamp for boosting energy levels in the morning.
- Start shifting to purple lighting 1-2 hours before your target bedtime to wind down.
- Consider your light sensitivity. Those more prone to migraines may still react to purple wavelengths.
- Use purple bulbs in combination with red and amber lights to create an ultra sleep-friendly noche-light environment.
Start with using purple lighting before bed for a few weeks to see if you notice improved sleep quality, longer sleep duration, and better mood stability during the daytime. But make sure to still prioritize good sleep habits like limiting evening screen use, avoiding caffeine late in the day, and keeping the bedroom comfortable and dark.
Conclusion
Early research suggests that purple LED light in the 430-460 nm range, especially narrow-band purplish-blue light centered around 420 nm, may have some benefits for sleep by stimulating melanopsin retinal cells less than standard blue LEDs. Using smart LED bulbs programmed to gradually shift to dimmer, warmer purple hues before bedtime aligns with the natural sunset changes in color and brightness. This could help facilitate our circadian rhythms, increase drowsiness at night, and improve sleep quality. But more controlled human studies on a wider population are still needed to determine the effects of purple light versus other visible wavelengths on sleep and health. When used properly, purple LED lighting does appear to be a safer choice for the hours leading up to bed compared to cool white or blue-enriched light.
