How the comparison works

Every result is one of these, worked out only from the device’s own figures (or a labelled MedcoVet measurement) and arithmetic:

• Within WALT’s range: the light in the wavelength band that counts for this target falls inside WALT’s irradiance range, so it delivers WALT’s dose in about WALT’s time per spot.
• Above WALT’s irradiance range: stronger than WALT’s upper figure, and the company gives no guidance on heat.
• Below WALT’s irradiance range: weaker than the lowest irradiance in WALT’s guideline. The page shows how far below, as a share of WALT’s minimum.
• No near-infrared for this depth: for deeper joints and the spine, the device’s own specifications show no light in WALT’s 780–860 nm near-infrared band. Red light isn’t fully blocked by skin, but very little of it reaches that deep.
• Device spec conflict: the company’s own figures disagree with each other, or with MedcoVet’s measurement, so the page doesn’t say whether the device is within WALT’s range. The conflict is listed under “Device conflict” in its specs. MedcoVet will compare it once the figures agree.
• Missing specs: the company doesn’t publish the figures needed (irradiance, or the power and treatment-head area to work it out), or its figures span more than one of these bands. The reason is given for each device.
• Not for home use without eye protection: a Class 3B or 4 laser, or a Risk Group 2–3 LED, under the international eye-safety standards (IEC 60825-1, IEC 62471).

WALT’s figures are draft guidelines for veterinary treatment; WALT hasn’t approved them as formal guidelines. Results depend on irradiance as well as dose: the same dose delivered at a different irradiance doesn’t reliably give the same result (Huang et al. 2009 review). In one study, with the dose fixed at 5 J/cm², only one of four irradiances tested improved healing (Lanzafame et al. 2007). So a device below WALT’s irradiance range can’t be assumed to match WALT’s results by treating for longer, and the page doesn’t show “time to reach WALT’s dose” for those devices.

For deeper targets, light also weakens as it passes through skin and tissue, so a device that is below WALT’s range at the skin delivers even less at the joint.

Total treatment time

For each device the page also shows how long it would take to deliver WALT’s dose over the whole treatment area, so you can judge whether the routine is practical at home. It’s worked out from the device’s average power where that’s published, or otherwise from the number of placements of its treatment head. No result depends on it. The treatment areas are MedcoVet drafts, and for devices below WALT’s range the time is shown for practicality only, not as an equivalent treatment.

Which light counts

The bands are WALT’s. WALT’s draft veterinary guidelines give its doses for near-infrared at 780–860 nm, and for superpulsed lasers at 904/905 nm. It describes red at 630–690 nm as typically used for superficial tendons, skin conditions and wounds, and notes it may be unsuitable for targets deeper than 1–2 cm. So for wounds and shallow joints (paw, carpus, tarsus), red and near-infrared both count; for deeper targets, only near-infrared in WALT’s band counts. Light outside these bands, such as 875 nm or 940 nm infrared, isn’t covered by WALT’s doses, so it isn’t counted. Skin absorbs red far more strongly: a review of laser studies by Bjordal and colleagues estimated that the skin barrier absorbs about 90% of continuous red light (632 nm) and about 80% of near-infrared (820 nm). Where a company doesn’t publish its red/near-infrared split, the near-infrared share runs from all to none.

Superpulsed 904–905 nm lasers are compared against WALT’s superpulsed doses, which are lower, and combined with a device’s other light by dose fraction. They get no extra credit for penetration: an earlier claim that superpulsing bleaches the skin and lets more light through over time was not borne out when Anders and Wu tested it, and in their study continuous 810 nm light passed through skin better than superpulsed 904 nm light.

Coat

Fur changes how much light reaches the skin, often by more than the difference between devices. WALT’s doses assume an unclipped light coat, so a light coat is the baseline. WALT’s guidelines don’t mention shaved skin or dark or black coats. For those, the figures on this page are MedcoVet’s estimates, not WALT’s, made by adjusting WALT’s light-coat range using Hochman-Elam and colleagues’ study of 47 dogs (2020), which measured light passing through the skin of white, brown and black dogs before and after shaving:

• Shaved: about 2.2 times the light of a light coat. The study’s statistical model gives about 2.2 times if it used a natural logarithm, or about 6.5 times if it used base 10; the paper doesn’t say which, so the page uses the lower figure. The real benefit may be larger, especially for darker coats.
• Dark (brown) coat: about one-third of the light of a light coat, from the study’s median measurements (0.3% vs 0.9%). The adjusted model suggests the loss may be smaller, so this is the cautious figure.
• Black coat: the median light through unshaved black coats was zero, so the page doesn’t compare devices for black coats and suggests shaving first. The authors recommend shaving before treatment, especially for darker dogs.

Fur-parting devices: a device that parts the fur at the point of contact, such as the Luma’s optical comb, reaches the skin and gets around the fur, so the coat no longer applies: it’s treated like shaved skin (about 2.2 times a light coat) whatever the coat’s thickness or colour, black included. This is MedcoVet’s assumption, not a measured figure: no published study has tested devices that part the fur. It applies to any device that parts the fur, not only MedcoVet’s. MedcoVet plans to measure it and publish the method and results.

Where the study’s figures are uncertain, the page uses the one that gives less light, so it doesn’t overstate what reaches your pet. The study used near-infrared lasers (810/980 nm and 904 nm) pressed onto the coat. Melanin absorbs red light more strongly, so coat likely matters even more for red light, and the study didn’t test devices that part the fur. Coat length wasn’t a significant factor in its results. Wounds are clipped, so coat doesn’t apply to them.

Figures and labels

Each figure is labelled with where it comes from: Seller’s figure MedcoVet measurement (interim) Arithmetic Research estimate MedcoVet assumption. MedcoVet’s solar power meter reads LED light high, so each of its readings is shown as a range, from the reading ÷ 20 to the reading ÷ 13. A power stated as “up to” or not stated as average is treated as an upper bound only. The treatment areas used for the whole-area times are MedcoVet drafts.

The headline results are for WALT’s 50 lb reference dog. The cat results use WALT’s 10 lb cat chart (2.7 J/cm² at 30–100 mW/cm², or up to 250 for the hip).

References

1. WALT Veterinary Dosage Recommendations Task Force. Draft veterinary photobiomodulation dosage guidelines (canine and feline stationary cluster charts), 2019. Draft for veterinary treatment; not approved WALT guidelines.
2. Hochman-Elam LN, Heidel RE, Shmalberg JW. Effects of laser power, wavelength, coat length, and coat color on tissue penetration using photobiomodulation in healthy dogs. Can J Vet Res 2020;84(2):131–137.
3. Bjordal JM, Couppé C, Chow RT, Tunér J, Ljunggren AE. A systematic review of low level laser therapy with location-specific doses for pain from joint disorders. Aust J Physiother 2003;49:107–116.
4. Anders JJ, Wu X. Comparison of light penetration of continuous wave 810 nm and superpulsed 904 nm wavelength light in anesthetized rats. Photomed Laser Surg 2016;34(9):418–424.
5. Huang Y-Y, Chen AC-H, Carroll JD, Hamblin MR. Biphasic dose response in low level light therapy. Dose-Response 2009;7:358–383.
6. Lanzafame RJ, Stadler I, Kurtz AF, et al. Reciprocity of exposure time and irradiance on energy density during photoradiation on wound healing in a murine pressure ulcer model. Lasers Surg Med 2007;39:534–542.
7. Hode L. Penetration of light into living tissue (review essay, citing Norris KH in Smith KC, ed. The Science of Photobiology, 1977).

Conflict of interest: MedcoVet publishes the WAIT Test and makes the Luma, one of the devices compared here. The Luma is compared in exactly the same way as every other device, as it ships today (1,010 mW, of which 606 mW is near-infrared). A higher-power version is being tested and will be added once it ships and has been measured.