White Paper: Clinical Studies on Pulsed Vs Continuous Red Light

Below is a white paper summarizing 9 studies comparing pulsed and continuous red light. 6 of 9 studies found pulsed light to be more effective than continuous red light. 1 study found them equally effective and 2 found continuous red light to be slightly more effective. The Cocoon has Continuous Red Light and 2 frequencies of Pulsed Light modes so that both forms of red light therapy can be applied. 

Most scientists that study pulsed red light hypothesize that pulsed red light is able to penetrate more deeply into the tissue than continuous light as one cause of the heightened efficacy for certain therapeutic effects.

resource NIH National Library of Medicine: https://pmc.ncbi.nlm.nih.gov/articles/PMC2933784/ 

STUDIES COMPARING CW AND PW

In this review thirty-three studies involving pulsed LLLT were examined. Of these studies, nine of them directly compared continuous wave (CW) with pulsed wave (PW) light, as recorded in Table 1. Six of these nine studies found PW to be more effective than CW. One study comparing CW and PW found both modes of operation to be equally effective, with no statistically significant difference between the two. Only two of the nine articles reported better results with CW than PW, although in both of these studies PW treated subjects were found to have better outcomes than placebo groups. One of the recurring limitations of the papers in this review was that like for like irradiation parameters were not used. For instance, Gigo-Benato et al. [23] found CW superior to PW in nerve regeneration, but is this because of the mode of operation (CW or PW) or because the CW laser used 808 nm and the pulsed laser used 905 nm?

Of the six studies that found PW to be more effective than CW, four of them involved the use of LLLT to cure the following pathologies in vivo: wound healing, pain, and ischemic stroke. The two remaining studies reported pulsing to be beneficial in vitro; in the first such study, PW promoted bone stimulation more so than CW. The other in vitro study comparing CW and PW found the latter mode of operation better able to penetrate through melanin filters, indicating that pulsing may be beneficial in reaching deep target tissue in dark-skinned patients.

In the wound healing study, Kymplova et al. [24] used a large sample size of women to study the effects of phototherapy on wound repair following surgical episiotomies (one of the most common surgical procedures in women). A pulsed laser emitted light (wavelength of 670 nm) at various frequencies (10, 25, and 50 Hz). The pulsed laser promoted wound repair and healing more so than the CW light source.

In the pain study, Sushko et al. [25] investigated the role of pulsed LLLT to attenuate pain in white male mice. The same wavelength of light was used as in Kymplova et al.’s study (670 nm), with the frequencies of 10, 600, and 8,000 Hz. Both modes of delivery (CW and PW) reduced the behavioral manifestations of somatic pain as compared to controls, but pulsed light (10 and 8,000 Hz in particular) was more effective.

The two studies involving pulsed LLLT and stroke were both done by Lapchak et al. [26]. Ischemic strokes were induced in rabbits, and a pulsed laser with a wavelength of 808 nm was used. In the first study, two frequencies of pulsed light were used (100 and 1,000 Hz), both of which reduced neurological deficits more so than CW. Accordingly, pulsed LLLT may play a major role in the management of stroke patients. Lapchak et al.’s second study attempted to prove the hypothesis that LLLT’s neuroprotective effect following stroke was a result of enhanced mitochondrial energy production (increased ATP synthesis) [27]. As with the previous study, LLLT was administered following stroke induction. CW radiation raised cortical ATP levels but was unable to bring them back to baseline. PW radiation, on the other hand, not only mitigated the effects of stroke on cortical ATP levels, but was able to raise cortical ATP levels to higher than those found in healthy rabbits (those in which stroke was not induced). This study provides valuable insight into one of the potential cellular and molecular mechanisms behind the enhanced neurogenesis (and improved clinical outcomes) observed in subjects receiving transcranial LLLT following stroke.

One of the nine studies reviewed found CW and PW to be equally effective in the promotion of wound healing. This study compared the effects of a CW laser (632.8 nm) and a PW laser (904 nm) on the promotion of wound healing in rabbits. Both lasers improved tensile strength during wound healing, but did not significantly improve wound-healing rates. A combined laser (CW+PW) was also tested. All three of the laser regimens improved tensile strength to a similar extent.

As mentioned earlier, there were nine studies that compared CW and PW, only two of which found CW to be more effective. These two studies involved wound healing and nerve regeneration respectively. Al-Watban and Zhang [28] study involved rats that were inflicted with aseptic wounds. The rats were divided into three groups: a control group, those irradiated with continuous wave light, and those irradiated with pulsed light at various repetition rates (100, 200, 300, 400, and 500 Hz). Of the pulse repetition rates administered, 100 Hz was the most efficacious and 500 Hz the least. Both CW and PW (635 nm) promoted wound healing, but CW was more efficacious. These results conflict with earlier studies that found pulsed light to be more beneficial in the promotion of wound healing. However, it should be noted that the difference between CW and PW treated subjects was small (a relative wound healing rate of 4.81 as compared to 4.32).

The second study that found CW to be more effective than PW involved nerve regeneration. There were three articles involving nerve regeneration, all of which found pulsed LLLT to be ineffective, as discussed in the section below entitled “Studies Involving Nerve Conduction and Regeneration.” Of these three, only Gigo-Benato et al. [23] compared CW (808 nm) and PW (905 nm). This study involved rats in which the left median nerve was completely transected and then repaired by end-to-end neurorrhaphy. The CW laser (808 nm) promoted faster nerve and muscle recovery than the pulsed laser (905 nm). However, Gigo-Benato also tested a combination of the CW and pulsed lasers, finding this to be the most effective of all. In other words, seven of the nine studies comparing CW and PW found pulsing to play a beneficial role. Only one of the nine studies found no role of PW, and even in this study the benefit of CW over PW was minimal.