I believe I have the right sources for you. It took a while. They don't use this therapy so much on this side of the pond, but there has been work done with it "over there."
Light therapy isn't exactly a ridiculous concept. For instance exposure to sunlight causes the body to manufacture vitamin D. And vitamin D has proven to be one of the more important vitamins for general health, never mind bone health.
Low level laser therapy (LLLT) is light at a specific frequency, intensity, and over a specific period of time. The best I can tell is they really don't understand the mechanism for its various physiologic effects. Sooo... without firm mechanisms one does have to wonder.
Ian commented on LLLT and hair regrowth. There's actually evidence in the literature for that. It was accidentally discovered by Mester in 1967 when attempting to use lasers on skin tumors. He noted that the laser light caused shaved mice to get hair regrowth faster than the mice not exposed to said laser.
As I suspected, most of the veterinary use is with pain management. But I can't find any evidence that it will help in the case of your dog with the herniated disk. In fact, I found this meta analysis that showed no effect. I've posted it below.
Low level laser therapy for nonspecific low-back pain
Reza Yousefi-Nooraie1, Eva Schonstein2, Kazem Heidari3, Arash Rashidian4, Victoria Pennick5, Marjan Akbari-Kamrani3, Shirin Irani3, Behnam Shakiba3, Sara Mortaz Hejri3, Ahmad-Reza Jonaidi3, Soroush Mortaz-Hedjri6
1Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Canada. 2Faculty of Health Sciences, University of Sydney, Lidcombe, Australia. 3Student's Scientific Research Center, Tehran University of Medical Sciences, Tehran, Iran. 4Centre for Academic and Health Policy, Tehran University of Medical Sciences, Tehran, Iran. 5Institute for Work & Health, Toronto, Canada. 6Systematic Review Study Group, Students' Scientific Research Center, Tehran University of Medical Sciences, Tehran, Iran
Contact address: Reza Yousefi-Nooraie, Clinical Epidemiology and Biostatistics, McMaster University, 1200 Main Street West, HSC 2C7, Hamilton, ON, L8N 3Z5, Canada. firstname.lastname@example.org
Editorial group: Cochrane Back Group.
Publication status and date: Edited (no change to conclusions), published in Issue 1, 2009.
Review content assessed as up-to-date: 13 November 2007.
Citation: Yousefi-Nooraie R, Schonstein E, Heidari K, Rashidian A, Pennick V, Akbari-Kamrani M, Irani S, Shakiba B, Mortaz Hejri S, Jonaidi AR, Mortaz-Hedjri S. Low level laser therapy for nonspecific low-back pain. Cochrane Database of Systematic Reviews 2008, Issue 2. Art. No.: CD005107. DOI: 10.1002/14651858.CD005107.pub4.
Copyright © 2009 The Cochrane Collaboration. Published by John Wiley & Sons, Ltd.AbstractBackground
Low-back pain (LBP) is a major health problem and a major cause of medical expenses and disablement. Low level laser therapy (LLLT) can be used to treat musculoskeletal disorders such as back pain.Objectives
To assess the effects of LLLT in patients with non-specific LBP.Search strategy
We searched CENTRAL (The Cochrane Library 2005, Issue 2), MEDLINE, CINAHL, EMBASE, AMED and PEDro from their start to November 2007 with no language restrictions. We screened references in the included studies and in reviews and conducted citation tracking of identified RCTs and reviews using Science Citation Index. We also contacted content experts.Selection criteria
Randomised controlled clinical trials (RCTs) investigating LLLT to treat non-specific low-back pain were included.Data collection and analysis
Two authors independently assessed methodological quality using the criteria recommended by the Cochrane Back Review Group and extracted data. Studies were qualitatively and quantitatively analysed according to Cochrane Back Review Group guideline.Main results
Seven heterogeneous English language RCTs with reasonable quality were included.
Three small studies (168 people) separately showed statistically significant but clinically unimportant pain relief for LLLT versus sham therapy for sub-acute and chronic low-back pain at short-term and intermediate-term follow-up (up to six months). One study (56 people) showed that LLLT was more effective than sham at reducing disability in the short term. Three studies (102 people) reported that LLLT plus exercise were not better than exercise, with or without sham in the short-term in reducing pain or disability. Two studies (90 people) reported that LLLT was not more effective than exercise, with or without sham in reducing pain or disability in the short term.
Two small trials (151 people) independently found that the relapse rate in the LLLT group was significantly lower than in the control group at the six-month follow-up.
No side effects were reported.Authors' conclusions
Based on the heterogeneity of the populations, interventions and comparison groups, we conclude that there are insufficient data to draw firm conclusions on the clinical effect of LLLT for low-back pain.
There is a need for further methodologically rigorous RCTs to evaluate the effects of LLLT compared to other treatments, different lengths of treatment, wavelengths and dosages.