Purple Light Therapy: What Red and Blue Light Do Together
Purple light therapy is red and blue light switched on together. There is no purple wavelength: the eye blends the two colours into purple, and the evidence behind the setting is the research on combined red and blue light for acne, where trials recorded falls of 76 to 77% in inflamed spots over 12 weeks. This article explains what each half of the light does, how "purple" differs from true violet light at 405 to 420 nm, what the trials found and how they were run, who should take care with blue light, and how to set up a red and blue session at home.
What is purple light therapy?
It is a setting that runs red and blue LEDs at the same time. It is named for the colour your eye sees, not for a wavelength.
Purple is not on the spectrum: it is what the eye reports when red and blue arrive together. So when a device lists a purple mode, check which two wavelengths it combines. The common pairing is blue at about 415 nm with red at about 630 to 660 nm, and that pairing is what the research tested. Our overview of LED light therapy colours sets purple alongside red, blue, green and yellow.
Is violet light the same as purple light?
No. Violet is a real band of light at the short end of the visible spectrum, about 380 to 450 nm, while purple on a device is a mix of red and blue.
Acne devices sold as "violet" or "high-intensity blue" emit at about 405 to 420 nm, and a 2021 systematic review notes that much of the 405 to 450 nm range usually described as blue is better called violet. Sensors, 2021 That band sits on the absorption peak of the molecules that acne bacteria produce, which is why so many trials used it. In three studies of a 405 to 420 nm source, eight sessions of 8 to 15 minutes twice a week reduced inflamed spots by 59 to 67%, and "No adverse effects or patient discomfort were noted in any of the patients." Journal of Cosmetic and Laser Therapy, 2003 In a trial of 124 people reported in the 2021 review, 407 to 420 nm light for 15 minutes twice a week over six weeks reduced spots by 76%, against 60% for 4% benzoyl peroxide. Sensors, 2021
What does the blue part of purple light do?
It targets acne bacteria. The bacteria make light-sensitive pigments called porphyrins, and when blue light excites them they release reactive oxygen that damages the bacteria.
Porphyrins absorb light from 400 to 700 nm, and 415 nm is the wavelength they absorb most effectively. Indian Dermatology Online Journal, 2015 In a laboratory study, 407 to 420 nm light cut the number of live acne bacteria by four log units, or 99.99%, after two exposures 24 hours apart, and by five log units after three. FEMS Immunology and Medical Microbiology, 2003 Blue light stays near the surface, reaching from a fraction of a millimetre to about 1 mm into the skin, where the bacteria live. The full picture of blue on its own is in our guide to blue light therapy.
What does the red part add?
Red light reaches one to two millimetres deeper than blue and is linked with calming inflammation. That is the reason for pairing them: one colour works on the bacteria near the surface, the other on the redness and swelling around a spot.
DermNet describes the combination as superior to blue alone because the two act at different depths. DermNet A 2015 review links red light with effects on the oil glands and on inflammation, by "influencing cytokine release from macrophages". Indian Dermatology Online Journal, 2015 In a mouse model of acne, 650 nm red light reduced inflammation more than 830 nm near-infrared did. Annals of Dermatology, 2016 The authors of the best-known trial proposed that the two work together, one antibacterial and one anti-inflammatory, though they did not test that mechanism.
Does purple light therapy work for acne?
For mild to moderate inflamed acne, combined red and blue light is one of the best-studied LED colour settings. Trials of red and blue together recorded falls of 76 to 77% in inflamed spots by week 12.
The key trial randomised 107 people with mild to moderate acne. Those who sat 25 cm (about 10 in) from lamps emitting 415 nm blue and 660 nm red for 15 minutes a day had 76% fewer inflamed spots after 12 weeks and 58% fewer blackheads and whiteheads. British Journal of Dermatology, 2000 A double-blind home trial in 35 people with skin types III to V used a 420 and 660 nm device for 2.5 minutes twice a day for four weeks. At week 12, inflamed spots were down 77% and blackheads and whiteheads 54%. Indian Dermatology Online Journal, 2015 By the investigators' rating, 14 of 18 treated people were clear or almost clear, against 2 of 17 using the sham device. Cochrane review, 2016
| Study | People | Light | Schedule | Result |
|---|---|---|---|---|
| Papageorgiou, 2000 | 107 (30 on red and blue) | 415 + 660 nm together, lamps | 15 min daily for 12 weeks | Inflamed spots down 76% |
| Kwon, 2013 | 35 (18 treated, 17 sham) | 420 + 660 nm together, home device | 2.5 min twice daily for 4 weeks | Inflamed spots down 77% at week 12 |
| Goldberg, 2006 | 22 completed | 415 and 633 nm, alternating, clinic | 8 sessions, twice weekly | Spots down 46% at week 4, 81% at week 12 |
| Lee, 2007 (in Ablon, 2018) | 24, all skin type IV | 415 and 633 nm, alternating | Twice weekly for 4 weeks | Inflamed spots down 77.9% |
| Sadick, 2008 | 21 | 415 and 633 nm, alternating, handheld | 8 sessions over 4 weeks | Inflamed spots down 69%, 8 weeks after the last session |
| Ershadi, 2025 | 6 trials, 216 people | Home devices, red 630 to 670 nm and blue 414 to 445 nm | 2 to 15 min twice daily | Inflamed spots 45.3% better than control |
In the 2025 analysis of home devices, inflamed spots improved by 45.3% and blackheads and whiteheads by 47.7% compared with control, with no serious side effects, and the authors noted that combined red and blue devices looked particularly effective. Dermatology Digest, 2025 The American Academy of Dermatology lists blue, red, and blue plus red devices among the lights that "can treat pimples". AAD How red light compares on its own is covered in red light therapy for acne.
Is red and blue together better than one after the other?
Both approaches have results. The two controlled trials ran red and blue at the same time, which is the true purple setting, while three open studies alternated the colours between sessions.
In the 2000 trial, red and blue together was ahead of blue alone at weeks 4 and 8, and the two were close by week 12, so the clearest gain from adding red was speed. The alternating studies used fewer, longer sessions: in one, 20 minutes of blue at 48 J/cm² and 20 minutes of red at 96 J/cm² on separate clinic visits. Journal of Cosmetic and Laser Therapy, 2006 What matters is the total time and dose, not the number of colours.
How often and how long should you use purple light therapy?
The trials used short, frequent sessions: daily or twice a day with lamps and home devices, or twice a week in clinics, for four to twelve weeks. With the panel, keep to the suggested 10 to 15 minutes per area.
The 2000 trial used 15 minutes a day for 12 weeks British Journal of Dermatology, 2000, the home-device trial 2.5 minutes twice a day for four weeks Indian Dermatology Online Journal, 2015, and the alternating studies two sessions a week for four weeks. Journal of Cosmetic and Laser Therapy, 2006 The panel is much brighter than those lamps, so stay within the suggested time and leave at least 6 hours between 30-minute sessions.
How long does purple light therapy take to work?
Expect to judge it at 8 to 12 weeks from the start. In most trials the sessions ran for four weeks and inflamed spots kept improving for weeks after they stopped.
In the handheld study, spots were still falling 8 weeks after the final session. Journal of Drugs in Dermatology, 2008 The AAD says "patients see the best results weeks after the last treatment", and that home devices are used twice a day. AAD Photos in the same light at weeks 0, 4, 8 and 12 show the trend best.
What does purple light therapy not do?
Its evidence is for inflamed spots in mild to moderate acne. Cysts and nodules are outside it, and blackheads and whiteheads usually improve less.
- Deep acne: the AAD does not count cysts or nodules among what these lights help, and adds: "Rarely can these treatments alone clear acne." AAD
- Blackheads and whiteheads: reviews describe smaller effects on these than on red spots. Indian Dermatology Online Journal, 2015
- Marks, scars and "hormonal" skin: the trials counted spots, and we found no trial behind claims that purple is a special colour for hormonal skin or scarring. Red and near-infrared for scars is a separate question, covered in red light therapy for scars and stretch marks.
Is purple light therapy safe for darker skin?
Red light caused no darkening in the study that compared the two colours, while blue can darken medium and darker skin. Start gently and watch for marks.
In a randomised study of volunteers with skin types III and IV, 415 nm blue light caused dose-dependent darkening that was still present three months later, while 630 nm red caused none. EMJ Dermatology, 2016 The response depends on skin type: in a study of visible light, types IV to VI developed darker, longer-lasting pigmentation from visible light than from UVA1, and type II showed none. Photochemical & Photobiological Sciences, 2020 On the other side, in the 2007 alternating study of 24 people with type IV skin, 14 reported a brighter skin tone. Dermatology Times
- Types III and IV: start with blue at a low setting, keep sessions short, try a small area first, and ask a dermatologist before starting if you are prone to melasma or dark marks.
- Daytime: a tinted sunscreen with iron oxides protects against visible light as well as ultraviolet.
- Types V and VI: our precautions advise against using the panel.
Does purple light therapy have side effects?
In the main trial, side effects with red and blue light were mild and uncommon. Dryness or itch affected 3.3% of users, against 32% of those using benzoyl peroxide.
A flare of spots and a rash were each reported by 6.6% and headache by 3.3% British Journal of Dermatology, 2000, and the 2025 analysis of home devices found no serious side effects. Dermatology Digest, 2025 Medium and darker skin needs a gentler start with blue, as set out above.
Do you need eye protection, and when should you use it?
Yes, keep your eyes covered or closed and never look into the diodes. Use red and blue sessions in the morning or afternoon rather than late in the evening.
The International Commission on Illumination places the peak of light's photochemical risk to the retina in the blue, at about 435 to 440 nm, and links the risk to staring into bright sources. CIE, 2019 Keep your eyes closed or covered during blue light sessions. More on this in is red light therapy safe for eyes. Blue light also signals daytime to the body clock, as set out in red light therapy morning or night.
Purple, blue or red: which should you choose?
For inflamed spots, red and blue together. For fine lines and skin texture, red with near-infrared.
Blue alone also has good acne evidence, and purple's edge in the 2000 trial was a faster start. Red suits skin where spots are not the main concern. For both goals, use separate sessions or a device that lets you choose its wavelengths.
Can you do purple light therapy with a Kivorla device?
On the panel, yes: you can run its blue and red together. The mask has no purple mode.
The 9-Spectrum Red Light Therapy Panel has 480 nm blue and 630 and 660 nm red among its nine wavelengths, and each one dims from 1 to 100% on its own, so blue and red can run in the same session. That is the same red and blue pairing a purple setting uses. Most acne trials used blue at 415 to 420 nm, a shorter wavelength than the panel's 480 nm. To set up a session:
- Wavelengths: raise 480, 630 and 660 nm, and turn the others down to their lowest setting.
- Start low: the panel is much brighter than the lamps in the 2000 trial, so short sessions and a lower blue setting are a sensible start.
- Distance and time: about 12 in for the face or back. Set the timer with the controller.
- Eyes and timing: wear the supplied goggles, and keep blue sessions to the morning or afternoon.
The 4-Wavelength Red Light Therapy Mask works differently. The red mode is 665 nm red with 850 and 1064 nm near-infrared, and the blue mode pairs 460 nm blue with 850 nm near-infrared, so its blue setting runs with near-infrared rather than red. The red and blue results above come from red and blue light, so we do not apply them to the mask. The mask has an eye opening with no diodes over the eyes.
Read the precautions before using either device: neither is for use during pregnancy, with epilepsy, a thyroid condition or thyroid medication, photosensitising medication, or on broken skin. Standard shipping to the US, UK and Germany is free. Under our returns policy, you have 30 days: a device that is unopened with its seals intact is refunded less a 10% restocking fee, and one that has been opened but is undamaged and complete is refunded less 20%.
Kivorla devices are general wellness devices, not medical devices. The acne figures above come from published trials of other devices. If you have moderate to severe, cystic or scarring acne, or use prescription acne medication, speak to a dermatologist before adding a light device.