Lumbar pain, or low back pain, may be defined as pain or discomfort located from the lower portion of the costal margin to the gluteal folds, with or without referred pain in the legs. This pain is classified as non-specific lumbar pain when its cause is unknown, as well as chronic when it persists for longer than three months with the appearance of disabilities for activities of daily life. Treatments for low back pain are usually pharmacological, focusing on analgesics, muscle relaxants and anti-inflammatories. Although protective factors, such as exercise, healthy diet and functional training may mitigate the evolution of pain, physical disability due to pain and functional loss reduce quality of life. Photobiomodulation (PBM) can be defined as the therapeutic use of light sources to reduce inflammation and relief pain. In this context, the objectives of this study are to develop and evaluate the effectiveness of an application protocol of an LED cluster for the treatment of chronic low back pain in a randomized, double-blind clinical trial that will be conducted in the outpatient facility of Universidade Nove de Julho (Uninove). Patients with chronic nonspecific low back pain, who signs the Informed Consent Form approved by the Uninove Institutional Review Board will be included in the study. Treatment sessions will be performed with a LED cluster three times a week for 4 weeks (totaling 12 sessions) in the lumbar region, and the outcomes will be measured with the following evaluations: VAS - Visual Analog Scale; Roland-Morris Disability Questionnaire (RMDQ); Schöber test; Modified Oswestry Disability Questionnaire and Algometry.

Inclusion Criteria:

• Clinical symptoms of vertebral pain that do not respond to symptomatic treatment with anti-inflammatory drugs for at least 3 months;
• Moderate to severe pain measured by Visual Analogue Scale (VAS> 4);
• Diagnosis of chronic nonspecific low back pain (as previously defined);
• Signed Informed Consent Form to participate in the study and availability to visit the clinic for treatment and evaluations.

Exclusion Criteria:

• Presence of other osteomuscular and rheumatic diseases;
• Presence of symptoms and signs of osteomioarticular disease, even if without known diagnosis;
• Clinical signs and complaints of osteomioarticular pain in the lower limbs (hips and ankles), as well as in spinal region;
• Use of Photobiomodulation up to 90 days before the inclusion;
• Clinical signs of neuropathy, including radiculopathy and peripheral nerve injury;
• Presence of systemic inflammatory diseases (rheumatoid arthritis, Reiter arthritis, spondylitis ankylosing, generalized polyarthritis, neoplasia);
• Presence of metabolic or endocrine diseases;
• Presence of Fibromyalgia;
• Presence of serious psychiatric disorders with demands for specialist care;
• Use of steroids injections up to 48 hours before inclusion;
• Infection or tumor in the area of Photobiomodulation application;
• Presence of severe blood dyscrasias;
• Presence of blood clotting disorders (including local thrombosis);
• Use of oral anticoagulant;
• Presence of Affective Psychotic Disorder that hinders adherence to the treatment;
• History of lumbar surgery;
• Patients who submit to government benefits due to low back pain.

In the placebo group, the laser application will be simulated in the same way as the active group, but the device will be turned off.

The outcome assessor will not know to which group the patients belong.