Pulsed vs. Continuous Laser: Why should we care?

 

As discussed in the prior post, there are many ways Low Level Light devices can differ – wavelength, power, area of illumination, and so on. One difference however, which we feel does not get due attention, is pulsed versus continuous light emission.

 

Most light sources (for example the light bulbs in your home, and the screen on which you are reading this blog post), emit continuous wave light, that is at a constant intensity, which appears unchanging to the naked eye.

 

Pulsed wave emission on the other hand involves turning on and off the light source many times per second. The Original LaserCap emits pulsed light, which gives it a characteristic “flicker.” There is a rhyme and reason to this, other than more attention for patients when they wear their LaserCap out to the nightclub.

 

 

A primary advantage of pulsing is improved heat management. Essentially the “off” period during pulsing (aka the “quench” period) allows the laser to cool, and compared to continuous laser, generates less heat at a given level of intensity [1].

 

Incredible amounts of energy can in fact be safely delivered with pulsed light. In one study for example, researchers illuminated the heads of rats using both continuous and pulsed light at a peak intensity of 750 mW/cm2 – over 100x the intensity of the LaserCap. The brains of rats exposed to continuous light were fried due to the heat, and they displayed severe neurological deficits. On the other hand absolutely no neurological or other tissue damage was found in the rats exposed to pulsed light [2].

 

Of course this is an extreme example – LLLT whether continuous or pulsed has been proven time and time again to be 100% safe, as it involves only a tiny fraction of the energy used in this study, which means any heat-related ill effects are limited to minor discomfort. However the principal remains – pulsed laser can be used to deliver larger amounts of energy, deeper into tissues, with greater comfort for patients.

 

Lasers furthermore do not work very well when they heat excessively. Specifically this can cause their power output to drop dramatically, resulting in an inconsistent and unpredictable dose delivered to the patient.

 

Even small barely perceptible amounts of excess heat can cause this. In fact, we tested the power output of several other laser cap brands which use continuous illumination, and compared these to the Original LaserCap, using pulsed illumination. We found that the power output of the off-brand continuous laser caps dropped by over 30% during the manufacturers’ recommended 5-6 minute treatment times. The pulsed Original Laser Cap on the other hand, when turned on for over 30 minutes, showed no drop in power [3].

 

In addition to superior comfort and more consistent output at higher treatment intensities, a number of studies have demonstrated LLLT with pulsed light to be more effective than that using continuous light [1]. This is likely at least partially due to the fact that pulsing allows for higher peak intensities and thus greater penetration into tissues. However research is revealing several other potential explanations.

 

One is that some biological processes operate with characteristic frequencies and/or other time scales, ranging from several to thousands of cycles per second. It is theorized that pulsing light in the correct way can better “sync” with, and consequently better optimize these processes. Examples of such processes implicated in the mechanism of LLLT include opening and closing of ion channels, and the photodissociation of nitric oxide [1].

 

Furthermore pulsed light may limit the filtering effect of melanin, a well-known pigment found in skin and hair. Melanin has been implicated as a cause of poor phototherapy outcomes in individuals with darker skin types, as it is highly absorptive of wavelengths in the visible and UV spectrum, and therefore can filter out substantial amounts of light, leaving less available to target cells. Studies have shown that, relative to continuous light, pulsed light can more easily penetrate through melanin-rich substances [4]. This has important implications for hair restoration, as individuals with darker hair and skin may benefit more from a pulsed LLLT treatment versus a continuous treatment [1].

 

There are advantages to continuous treatments as well however, namely shorter time of treatment needed for equivalent dose. The most effective LaserCap is of course the one that is used, so a continuous option may be more suitable for patients with busy schedules or desiring greater convenience.

 

We believe that our prescribing physicians should decide whether to recommend a continuous or pulsed treatment, based on their evaluation of the best available evidence, and the individual needs of their patient. This is why we provide both pulsed and continuous options on all of our LaserCap models.

 

The LaserCap moreover is designed for superior ventilation making it uniquely suited for continuous output. We give our competitors credit – they all provide a nice looking product. But it seems that is about all. In many cases their enclosures, although aesthetically pleasing, are heat traps, which is why their output can drop by over 30% over a short 5-6 minute period of time [3].

 

While any continuous treatment will result in some power loss, a little ventilation can go a long way. The Original LaserCap loses only 10% power with comparable starting output and time. The Original LaserCap 300 moreover can deliver almost 4x the intensity of the most popular off-brands – and lose only around 20% power during 5 minutes of continuous illumination [3].

 

Furthermore our newest LaserCap model, the MC2, with its unique, patent-pending vented design has even greater ability to manage heat. When we tested the MC2 in continuous mode at an intensity nearly 3x the intensity of similar off-brand caps – power dropped by less than 9% over the 5 minute treatment time [3].

 

Stay tuned for more of this original data from our optics lab!

 

 

 

  1. Hashmi JT, Huang Y-Y, Sharma SK, et al. Effect of pulsing in low-level light therapy. Lasers Surg Med. 2010;42(6):450-466. doi:10.1002/lsm.20950. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2933784/
  2. Ilic S, Leichliter S, Streeter J, Oron A, DeTaboada L, Oron U. Effects of power densities, continuous and pulse frequencies, and number of sessions of low-level laser therapy on intact rat brain. Photomed Laser Surg. 2006;24(4):458-466. doi:10.1089/pho.2006.24.458
  3. Internal data on file
  4. Brondon P, Stadler I, Lanzafame RJ. Pulsing influences photoradiation outcomes in cell culture. Lasers Surg Med. 2009;41(3):222-226. doi:10.1002/lsm.20740

 

 

Thanks to Dr. Michael Hamblin and Dr. Bob Haber for their contributions to this post