• Change in disability assessed by Roland-Morris Disability Questionnaire (RMDQ) [ Time Frame: Baseline (Before the first application of LED) and 4 weeks after (after the last application). ]
  This scale assesses physical abilities and psychological factors of patients, inquiring about functional changes of people with low back pain. It presents 24 questions about the conditions of the patient that characterize the presented incapacity. In all questions the phrase "because of my back" is added, and when it comes to answering them, the patient signals only the phrases that best suits him or her at that moment, otherwise the patient should go on to the next sentence. The total count of the marked items can range from a minimum of zero, considered no functional impairment, to a maximum of 24, high functional impairment.
• Change in range of motion assessed by Schöber test [ Time Frame: Baseline (Before the first application of LED) and 4 weeks after (after the last application). ]
  the patient will remain in the orthostatic position while the examiner positions his thumbs at the lower margin of the posterior superior iliac spine (PSIS) and draws a horizontal line in the midline between these two structures. Then, the examiner firmly holds the tip of a measuring tape against the patient's skin on the marked line and marks a second line 15 cm above the first. The patient is then asked to flex the anterior trunk without increasing pain and a new measurement is marked between the lower and upper marks; finally, the patient returns to the neutral position. The difference between the initial distance (between the two marks on the skin in the neutral position) and the new measurement in the flexed position indicates the mobility of the lumbar spine in centimeters, with precision of millimeters.
• Change in disability assessed by Modified Oswestry Disability Questionnaire [ Time Frame: Baseline (Before the first application of LED) and 4 weeks after (after the last application). ]
  The Brazilian version of the Oswestry questionnaire allows the evaluation of the functional disability reported by the patients, based on the level of pain during different activities of daily life. This questionnaire contains ten questions about daily activities for evaluating the impact of pain on the performance of such activities. The results range from zero (minimum disability) to 100 (evident disability).
• Change in Pressure Pain Threshold [ Time Frame: Baseline (Before the first application of LED) and 4 weeks after (after the last application). ]
  The Pressure Pain Threshold (PPT) will be evaluated with the J Tech algometer (XXX). The algometer is a hand device with a 1cm² diameter rod and a rubber cover in its tip. It allows the recording, through the electronic device, the pressure applied on a surface. For this evaluation, a pressure will be applied at a constant rate of 1kg/sec to the level at which pain or discomfort is reported by the volunteer who will be lying on a stretcher. The evaluated muscles will be: gluteus medius; tensor fasciae latae; tibialis anterior; proximal ischiotibial (ischium); paravertebral muscle (lumbar L2-L5 and sacral S1-S3).

• Radiation: LED Photobiomodulation
  A total of twelve laser applications (3 sessions per week) will be provided to the patients as treatment. A LED board with wavelengths of 660nm and 850nm at 5mW of power will be used for 30 minutes, resulting in a total energy of 3J per point in each session. The application site will be the lumbar region, in contact with the skin. The LED cluster (light-emitting diodes) has 72 LEDs.
• Other: Placebo LED Photobiomodulation
  For the placebo group, the procedures will be the same, however the LED equipment will remain off.

• Active Comparator: Active group
  Thirty eight patients will be recruited from UNINOVE outpatient units and randomly allocated in the two groups.
  Intervention: Radiation: LED Photobiomodulation
• Placebo Comparator: Placebo group
  Thirty eight patients will be recruited from UNINOVE outpatient units and randomly allocated in the two groups.
  Intervention: Other: Placebo LED Photobiomodulation

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.