How does light therapy work?

Light interfaces with cycle and hormone biology through two complementary routes:

• Circadian & neuroendocrine signaling: Timed bright light influences central clock outputs that regulate melatonin, cortisol, and reproductive axes. In women with late luteal phase dysphoric disorder (LLPDD/PMDD), bright light shifted hormonal rhythms (e.g., cortisol/prolactin) and improved symptoms in crossover trials (Parry et al., 1994; Parry et al., 1989; Lam, 1999). Wavelength composition also affects HPA-axis dynamics in humans (Robertson-Dixon et al., 2023).

• Photobiomodulation (PBM) for localized comfort: Red/near-infrared (≈630–850 nm) PBM can modulate cellular metabolism and nociceptive pathways. Randomized trials and syntheses report reductions in primary dysmenorrhea pain with LLLT compared to sham or active comparators (Hong et al., 2016; Shin et al., 2012; Thabet et al., 2021; Ang et al., 2025).

Together, these mechanisms suggest a practical pattern: morning bright light to strengthen circadian alignment and targeted red/NIR PBM for local comfort—kept within an informational, wellness context.

Applications for cycle & hormone balance

Light strategies can be woven into daily routines to support comfort and rhythm across the cycle or during transitions (e.g., perimenopause):

• Premenstrual mood & timing: Bright light protocols during the late luteal phase improved depressive/tension ratings in PMDD/LLPDD (Parry et al., 1989; Lam, 1999; see also systematic review Krasnik et al., 2005).

• Cycle comfort (dysmenorrhea): Local red/NIR PBM reduced menstrual pain in randomized and controlled studies (Hong et al., 2016; Shin et al., 2012; Thabet et al., 2021; Ang et al., 2025).

• Follicular-phase support: In women with slightly lengthened cycles, morning bright light in the follicular phase increased pituitary reproductive hormones and ovulation rates (Danilenko et al., 2007).

Key benefits at a glance

• Supports circadian alignment relevant to hormone timing and mood in PMDD/LLPDD (Lam, 1999; Parry et al., 1994)

• Local comfort for primary dysmenorrhea with red/NIR PBM protocols (Hong et al., 2016; Thabet et al., 2021; Ang et al., 2025)

• Evidence that wavelength composition can influence human HPA-axis outputs (cortisol) (Robertson-Dixon et al., 2023)

Note: Effects vary with spectrum, intensity, timing, and individual sensitivity; findings for PBM in mood/hormone contexts are evolving.

Who can benefit?

Individuals seeking to stabilize daily rhythms, support comfort during cyclical phases, or structure light for wellbeing. This page provides general information only.

How to use it in practice

Morning circadian support: Bright light soon after waking on most days; consider luteal-phase timing for PMDD protocols as studied (Lam, 1999).

Local comfort (dysmenorrhea): Short sessions of red/NIR PBM directed to the lower abdomen or low back, following parameters similar to clinical studies (Hong et al., 2016; Thabet et al., 2021).

Follicular-phase routine: Morning bright light during the follicular phase in individuals with slightly lengthened cycles (Danilenko et al., 2007).

Consistency is more impactful than intensity; align use with daily schedules and sensitivity.

Scientific context

Bright light therapy has shown benefits for premenstrual mood disorders and can shift related neuroendocrine rhythms in controlled studies (Parry et al., 1989; Parry et al., 1994; Lam, 1999; Krasnik et al., 2005). Independent work shows wavelength-dependent effects on the human HPA axis (Robertson-Dixon et al., 2023), while local red/NIR PBM has RCT-level evidence for primary dysmenorrhea (Hong et al., 2016; Thabet et al., 2021) and meta-analytic support (Ang et al., 2025).

These findings inform wellness-oriented light routines; they do not constitute medical claims for redtreat devices.

Why redtreat

We focus on research-informed light patterns—bright light tools for mornings and gentle red/NIR options for local comfort—designed for ease, consistency, and high build quality.

• Timing-first design: morning bright-light options; evening low-blue options

• Targeted PBM (≈630–850 nm) for localized comfort routines

• Swiss engineering for precision and reliability

Disclaimer

References are provided for educational and informational purposes. They summarize general research on light exposure, circadian systems, PMDD, and dysmenorrhea. They do not constitute therapeutic or clinical claims for redtreat products. Products are not intended to diagnose, treat, cure, or prevent any disease. Individuals with ongoing symptoms or medical conditions should consult a healthcare professional.

Scientific references

• Parry, B. L., et al. (1989). Morning vs evening bright light in late luteal phase dysphoric disorder. Psychiatry Research.
• Parry, B. L., et al. (1994). Neuroendocrine effects of light therapy in LLPDD. Psychiatry Research.
• Lam, R. W. (1999). Controlled crossover study of bright light in LLPDD. Psychiatry Research.
• Krasnik, C., et al. (2005). Systematic review: bright light therapy for PMDD. Am. J. Obstet. Gynecol. (Cochrane-style summary)
• Danilenko, K. V., et al. (2007). Morning bright light stimulates pituitary reproductive hormones and ovulation in women with slightly lengthened cycles. Chronobiology International.
• Robertson-Dixon, I., et al. (2023). Influence of light wavelength on human HPA-axis (cortisol) regulation. Scientific Reports.
• Shin, Y. I., et al. (2012). Skin-adhesive LLLT for dysmenorrhea (acupoint approach). Lasers Med. Sci.
• Hong, G. Y., et al. (2016). RCT: self-applied LLLT in primary dysmenorrhea. Int. J. Gynaecol. Obstet.
• Thabet, A. A., et al. (2021). HILT vs LLLT for primary dysmenorrhea: randomized trial. J. Phys. Ther. Sci.
• Ang, L., et al. (2025). Systematic review & meta-analysis: light therapy for primary dysmenorrhea. Photodiagnosis Photodyn. Ther.