Pain is where red light therapy has the most published trials and the least agreement about what they mean. Major treatment guidelines still do not recommend it. Several meta-analyses find a real effect. Both camps are reading roughly the same studies.
The reason they disagree is dose, and once you understand that, the literature stops looking contradictory.
The best evidence in the category
Stausholm and colleagues published a systematic review and meta-analysis in BMJ Open in 2019, pooling 22 randomized placebo-controlled trials with 1,063 knee osteoarthritis patients. It is the most careful piece of work in this space and it is worth reading the numbers rather than the headline.
Pooled across everything, low-level laser therapy reduced pain by 14.23 mm on a 0 to 100 visual analog scale at the end of the treatment period, with a 95 percent confidence interval of 7.31 to 21.14. At follow-ups one to twelve weeks later the reduction was 15.92 mm.
For context, the same paper notes that the pain-relieving effect of NSAIDs over placebo in knee osteoarthritis has been estimated at about 10.1 mm on the same scale.
The part that actually matters
The subgroup analysis is where this gets interesting. The authors split the trials by whether they used doses within the World Association for Laser Therapy recommendations.
Trials using recommended doses produced an 18.71 mm reduction at the end of therapy and 23.23 mm at follow-ups two to twelve weeks later. The effect peaked two to four weeks after treatment finished, at 31.87 mm beyond placebo.
Trials using doses outside those recommendations did not separate from placebo.
That is the whole story of this literature in one result. Underdose or overdose and you get nothing, which is exactly what the biphasic dose response predicts. Huang, Chen, Carroll and Hamblin described that curve in Dose Response in 2009 and it explains most of the apparent inconsistency across pain trials.
The doses that worked: 4 to 8 joules per treatment spot at 785 to 860nm, or 1 to 3 joules per spot at 904nm. Dosage covers how to convert that into a session length.
Neck pain
Chow and colleagues published a systematic review and meta-analysis in The Lancet in 2009 covering low-level laser therapy for neck pain. They reported pain reduction immediately after treatment in acute neck pain, and sustained benefit up to 22 weeks after the end of treatment in chronic neck pain.
That paper is often cited as though it settled the question. It did not. The authors themselves flagged variation in treatments and possible bias in the small trials included, and later methodologists criticized the use of a fixed-effects model given the heterogeneity, which would inflate the pooled effect.
Treat it as suggestive rather than definitive.
Low back pain
This is where the evidence is genuinely weak, and it is worth being blunt about it since back pain is what most people buy a pad for.
The Cochrane review by Yousefi-Nooraie and colleagues, published in 2008, found some evidence of short and intermediate-term pain relief compared with sham for subacute and chronic low back pain, but no difference from comparison groups on pain-related disability. The reviewers concluded there was insufficient data to draw firm conclusions.
Nothing since has decisively changed that picture. If a brand tells you red light is proven for back pain, they are ahead of the literature.
Muscle performance and recovery
Vanin and colleagues published a systematic review and meta-analysis in Lasers in Medical Science in 2018 on photobiomodulation for muscular performance and exercise-related fatigue in healthy people. The literature they reviewed points toward improvements in strength, repeated sprint performance and markers of muscle damage, particularly when light is applied before exercise rather than after.
Ferraresi, Huang and Hamblin covered the same territory in the Journal of Biophotonics in 2016.
The caveats are the familiar ones. Trials are small, protocols vary wildly, and the outcome measures are often laboratory tasks rather than competitive performance. The effect on delayed onset muscle soreness looks more consistent than the effect on raw output.
Why the guidelines still say no
Stausholm's own paper notes the situation plainly: low-level laser therapy is not recommended in major knee osteoarthritis treatment guidelines. The 2018 European League Against Rheumatism guidelines mentioned it without recommending it, and the 2018 Osteoarthritis Research Society International guidelines stated it should not be considered a core intervention.
Guideline committees are conservative and they weight trial quality heavily. Small studies with unclear blinding and inconsistent parameters do not move them, even when the pooled effect looks respectable.
That is a reasonable position, and it is also a reason to keep your expectations calibrated. The honest summary is that light may support pain reduction in knee osteoarthritis when the dose is right, and that this is not the same as an established treatment.
The gap between the trials and your panel
Here is the part almost nobody mentions. Most of the pain trials in these meta-analyses used clinic laser probes held in contact with the skin, delivering a defined number of joules to each of several marked treatment points around the joint.
Standing four feet from a wall panel is not that. Irradiance falls off sharply with distance, and the light also spreads over a much larger area, so the joules per square centimeter landing on your knee capsule is a fraction of what the protocol specified.
This is the strongest practical argument for contact devices in pain applications. NovaaLab publishes a distance curve for its Deep Healing Pad showing roughly 150 mW/cm2 at contact, 120 at one inch, 45 at three inches and 25 at six inches. Six inches costs you about five sixths of the intensity.
A wrap that touches the joint, or a strap-mounted device using 808nm laser diodes such as Kineon's MOVE+ Pro, maps far more closely onto what the trials actually did. Panel, mask, wrap or cap goes through this in detail.
Near-infrared also matters more here than anywhere else in the category, because visible red light does not reach a joint capsule. Wavelengths covers which numbers to look for.
What is reasonable to expect
The defensible claim is that a correctly dosed near-infrared device applied in contact with a painful joint may reduce pain over a course of several weeks, with the effect appearing to build after treatment ends rather than during it.
The claim it does not support is that any of this repairs cartilage, reverses arthritis or replaces medical care. No published trial shows structural change in a human joint.
If you are considering this for a diagnosed condition, talk to whoever is managing it. Safety covers the situations where you should check first.
FAQ
How many sessions before I would know? The trials ran courses of several weeks, and the Stausholm analysis found pain relief peaking two to four weeks after the course finished. That means judging it during week one is meaningless, and it also means the benefit may keep improving after you stop.
Panel or contact wrap for a bad knee? Wrap. The dose that matters is what lands on the joint, and contact devices deliver several times the irradiance a panel does at normal standing distance.
Are there side effects? The Stausholm meta-analysis reported no adverse events across 22 trials. That is reassuring, though it also reflects short trials with limited follow-up.
Is this a substitute for physical therapy or medication? No. Exercise therapy has substantially better evidence for knee osteoarthritis than light does, and nothing in this literature supports stopping a prescribed treatment.
Sources
- Stausholm MB, Naterstad IF, Joensen J, Lopes-Martins RAB, Sæbø H, Lund H, Fersum KV, Bjordal JM. Efficacy of low-level laser therapy on pain and disability in knee osteoarthritis: systematic review and meta-analysis of randomised placebo-controlled trials. BMJ Open. 2019;9(10):e031142. https://pubmed.ncbi.nlm.nih.gov/31662383/
- Chow RT, Johnson MI, Lopes-Martins RA, Bjordal JM. Efficacy of low-level laser therapy in the management of neck pain: a systematic review and meta-analysis of randomised placebo or active-treatment controlled trials. The Lancet. 2009;374(9705):1897-1908. https://pubmed.ncbi.nlm.nih.gov/19913903/
- Yousefi-Nooraie R, et al. Low level laser therapy for nonspecific low-back pain. Cochrane Database of Systematic Reviews. 2008;CD005107. https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD005107.pub2/abstract
- Vanin AA, Verhagen E, Barboza SD, Costa LOP, Leal-Junior ECP. Photobiomodulation therapy for the improvement of muscular performance and reduction of muscular fatigue associated with exercise in healthy people: a systematic review and meta-analysis. Lasers in Medical Science. 2018;33(1):181-214. https://pubmed.ncbi.nlm.nih.gov/29090398/
- Ferraresi C, Huang YY, Hamblin MR. Photobiomodulation in human muscle tissue: an advantage in sports performance? Journal of Biophotonics. 2016;9(11-12):1273-1299. https://pubmed.ncbi.nlm.nih.gov/27874264/
- Huang YY, Chen AC, Carroll JD, Hamblin MR. Biphasic Dose Response in Low Level Light Therapy. Dose Response. 2009;7(4):358-383. https://pubmed.ncbi.nlm.nih.gov/20011653/