How low can you go?

By Jan Tunér

Like other medical interventions, PBM follows the Arndt-Schultz law, postulating that too little has no effect and too much has a negative effect. This is well known, at least to most us. But the question is then, what is too low?

In the early days, some surprisingly positive studies used very low energies, around and below 1 mW (1,2,3,4), but back then only these very weak lasers were available. Today we have access to more suitable lasers and the outcome of interventions are much more effective.

Still, knowledge about where the approximate peak of “the therapeutic window” is located is surprisingly low. Here are a few examples…

Santos et al. (5) used 660 nm to treat pain and wound healing after episiotomy (see picture).

The laser had a power of 15 mW and was used on three points, each receiving 0.15 J and a total energy of 0.45 J.  This is obviously a homeopathic amount of energy.  So why used? Well, the dose was 3.8 J/cm² and possibly to authors did not know the necessity of having energy as well as dose within the therapeutic window. It is easy to obtain a fair value for the dose just by using a thin probe. So, the outcome of the paper is negative. For good reasons.

The same problem appears in the study by Brosseau (6). The authors report a reasonable dose (3 J/cm²) but the energy per point is 0.12 J! Still these authors dare to claim that “LPT is no better than placebo at reducing pain, morning stiffness, or improving functional status for OA-hand patients”. Same problem - ignorance about reasonable parameters. Still, Brosseau has been an early Cochrane “expert” of PBM and should at least have learned a bit along the way.

Lai (7) concludes that “Within the limits of this pilot study, the use of the low-power He-Ne laser as an adjunct to non-surgical periodontal therapy in patients with moderate to advanced chronic periodontitis did not seem to provide additional clinical benefit.” And he is right, and the limit was the use of a 0.2 mW laser (zero point two mW). Why?!

The only negative study on the use of PBM to prevent mucositis comes from Cruz (8). Looking at the PubMed abstract, it seems indeed that it does not. But although the dose was 4 J/cm², the energy per point was 0.18 J. Same problem – dose and energy not trivial choices.

My final example is more puzzling. Would 0.45 mJ (millijoule!) /cm² have an effect? And which “growing number of laboratory and clinical studies” have shown positive results from “ultra low level laser irradiation”?  What did I miss?  References, please?? Still, it is worth reading the abstract from Guiliani (9) to gain insight into the world of ‘homeopathic PBM’:

A growing number of laboratory and clinical studies over the past 10 years have shown that low-level laser stimulation (633 or 670 nm) at extremely low power densities (about 0.15 mW/cm²), when administered through a particular emission mode, is capable of eliciting significant biological effects. Studies on cell cultures and animal models as well as clinical trials give support to a novel therapeutic modality, which may be referred to as ultra low level laser therapy (ULLLT). In cultured neural cells, pulsed irradiation (670 nm, 0.45 mJ/cm²) has shown to stimulate NGF-induced neurite elongation and to protect cells against oxidative stress. In rats, anti-edema and anti-hyperalgesia effects following ULLL irradiation were found. Clinical studies have reported beneficial effects (also revealed through sonography) in the treatment of musculoskeletal disorders. The present paper reviews the existing experimental evidence available on ULLLT. Furthermore, the puzzling issue of the biophysical mechanisms that lie at the basis of the method is explored and some hypotheses are proposed. Besides presenting the state-of-the-art about this novel photobiostimulation therapy, the present paper aims to open up an interdisciplinary discussion and stimulate new research on this subject

A company believing in homeopathic laser use is Erchonia. Their 7 mW red widespread beam is supposed to go through clothes and furs. See examples below. Hardly any photons will reach the skin after trying to penetrate clothes and furs, and then further penetrate the skin. Sales are good, however. If you are still in doubt, check

So the question is, how low can you go? …and yet remain serious.


  1. Walker JB: Relief from Chronic Pain by Low Power Laser Irradiation. Neuroscience Letters. 1983; 43: 339-344.
  2. Walker J B et al. Laser therapy for pain of rheumatoid arthritis. Laser Surg Med. 1986; 6: 171.
  3. Snyder-Mackler L et al: Effect of helium-neon laser irradiation on skin resistance and pain in patients with trigger points in the neck or back. Physical Therapy. 1989; 69: 336-341.
  4. Snyder-Mackler L, Bork C, Bourbon B et al. Effect of Helium-Neon Laser on Musculoskeletal Trigger Points. Physical Therapy. 1986; 66 (7): 1087-1090.
  5. Santos J de O, Oliveira SM, Nobre MR, Aranha AC, Alvarenga MB. A randomised clinical trial of the effect of low-level laser therapy for perineal pain and healing after episiotomy: a pilot study. Midwifery. 2012; 28 (5): e653-659.
  6. Brosseau L, Wells G, Marchand S, Gaboury I et al. Randomized controlled trial on low level laser therapy (LLLT) in the treatment of osteoarthritis (OA) of the hand. Lasers Surg Med. 2005; 36 (3): 210-219.
  7. Lai S M, Zee K Y, Lai M K, Corbet E F. Clinical and Radiographic Investigation of the Adjunctive Effects of a Low-Power He-Ne Laser in the Treatment of Moderate to Advanced Periodontal Disease: A Pilot Study. Photomed Laser Surg. 2009; 27 (2): 287-293.
  8. Cruz LB, Ribeiro AS, Rech A, Rosa LG, Castro CG Jr, Brunetto AL. Influence of low-energy laser in the prevention of oral mucositis in children with cancer receiving chemotherapy. Pediatr Blood Cancer. 2007; 48 (4): 435-440.
  9. Giuliani A, Fernandez M, Farinelli M, Baratto L et al. Very low level laser therapy attenuates edema and pain in experimental models. Int J Tissue React. 2004; 26 (1-2): 29-37.