The concept behind the use of light to treat skin tissue is that light that is absorbed by tissue generates heat. By using specific colors (or wavelengths) of light to treat specific parts of the skin we can target and therefore treat a distinct part of the skin and spare surrounding tissue. Light can pass completely through non-absorbing tissue and effect subsequent tissue that absorbs its energy and thereby produces heat.

A “red” pen appears “red” because it reflects the color “red” back to the eye of the observer. This same “red” pen absorbs other colors such as blue, green, yellow, etc. Shining a “red” light, or laser on this “red” pen would produce no light absorption, and therefore no increased heat in the “red” pen. However, shining a “yellow” light or laser on the “red” pen would result in absorption of the “yellow” light and a heating of the pen. The amount of light and the duration of the beam of light would correlate with the rise in temperature of the pen. Above a certain temperature threshold the pen might be damaged. However, if the energy was delivered over duration of time that was too long, the heat produced might have sufficient time to spread beyond the pen and start to damage the paper or table on which the pen rested.

The basic principles involved require that the light delivered be at a color (or wavelength) that the target can optimally absorb, that the duration of the light enable the entire target to be heated to a proper level, without damage to, or wasting of energy on, the surrounding tissue that needs to be preserved.

The basic difference between pulsed light and lasers is that pulsed light in EpiLight or PhotoDerm etc. has hundreds of wavelengths (colors) of light in each burst of light, whereas lasers produce 1 wavelength (color) of light at a time. The colors delivered by EpiLight or PhotoDerm range between the frequencies of 515nm and 1200nm. This includes blue, green, yellow, and red colors. The expert operator can modify the wavelength to deliver a combination of wavelengths that can be longer (and thereby go deeper into the tissue) or shorter (and thereby penetrate less deeply into the tissue). Pulsed light EpiLight and Photoderm enable the expert user to adjust the duration of pulses over a wide range, and to deliver these bursts of light in varying combination and numbers. Each of these adjustments enables the operator to more specifically treat the target and spare the surrounding structures.

Lasers, on the other hand, produce one light color that is coherent (in phase) but which has a specific depth of penetration that usually cannot be adjusted, or have a very limited 15nm range of adjustment as compared to the 700nm range of pulsed light EpiLight or PhotoDerm.

The duration of the burst of light delivered is also a fundamental difference between pulsed light and lasers. Lasers were originally designed to deliver bursts of light in millionths of a second duration to treat microscopic sized particles such as tattoo pigment, melanin pigment (melanosomes), or the hemoglobin in red blood cells. These durations have produced less beneficial results when treating hair since the targeted “hair follicle” is far larger than the pigment, or even the “hair shaft” itself and, therefore, requires longer pulse durations of light than were originally available with lasers. As a result of these short durations, lasers have produced pigmentary changes of the remaining hair, or simply burnt the hair without adequately damaging the ”follicle” that continues to produce new hairs.

Lasers are now scrambling to correct their too short pulse duration. Newer lasers are being developed to increase the duration from the original microseconds (millionths of a second) or shorter. A laser developed by Palomar named the SLP1000 is a 810nm wavelength Diode laser that can increase the pulse duration of its 1 pulse up to 1,000 millisecond = one thousand thousandths of a second; which is equal to a 1 second duration. EpiLight, by comparison, can deliver up to 5 pulses, each of which has a maximum duration of 7 milliseconds, with four 300 millisecond intervals between the 5 pulses. Thus, EpiLight’s total pulse duration is 1500 (5x300) +28 (4X7) = 1528 millisecond = or 1.5 seconds. Since EpiLight has had this longer duration for almost 4 years ahead of the competition, there is much more experience using their settings. This experience and longer durations appear to improve the responses of larger hair follicles and to produce fewer side effects in darker skin types. For over 5 years I have personally been safely and effectively treating even the most difficult to treat type 6 (Black) skin types patients who have unwanted hair, using my own settings on EpiLight.

I am currently using special settings and techniques for testing tanned skin safely. However, when possible it is preferable to treat skin that has not been tanned in the past 1-2 months.