IPL Features: State-of-the-Art

By:  Gary Ruf, Owner, R&D Aesthetics

This memo covers features offered by state-of-the-art Intense Pulsed Light (IPL) technology and the benefits availed by them.  The features and benefits apply to all high-power pulsed-light modalities – LASERs as well as IPL devices.  This is because the major advances in this field have been made in the circuitry (power supplies, pulse formation circuits, microprocessor switching and control), flash lamp design and cooling systems.  These are all components that are common to IPL and LASER.

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Background

I have over twenty years experience in designing, testing, using and repairing aesthetic lasers (Alexandrite, CO2, Diode, Erbium, Nd:YAG, PDL, Ruby and “fractional” versions thereof) as well as IPL devices.  I was a “laser snob” during the first ten years of my career.  LASERs are sophisticated pieces of equipment that are powerful and precise.  Not all lasers are created equal but the proper device, in the hands of an experienced and knowledgeable operator, can produce results that are nonpareil to other methodologies.

In recent years IPL devices have been developed that generate photonic (light) power equaling that of LASER technology.  IPL emits the entire spectrum of wavelengths suitable for almost all non-ablative (non-surgical) aesthetic treatments.  One IPL device can match the capabilities of numerous lasers.  A single $20,000 IPL device can produce similar results as several LASERs costing over $80,000 a piece!

I have been privileged to work with many leading domestic brands of IPL including:

• Cutera Medical – Lime Light and Xeos + IPL
• Focus Medical – NaturaLight
• Lumenis – EpiLight
• Novalis – Clareon
• Palomar/Cynosure – Medilux, Starlux 300, Starlux 500 and Icon
• Radiancy – SpaTouch and Kona
• Syneron/Candela – elōs

I have designed and constructed a powerful IPL prototype for a domestic (US) manufacturer, consulted with the engineering and marketing departments of two other large domestic manufacturers and was alpha (prototype) tester for other new designs.

Chinese and Taiwanese manufacturers have made great advances in the design, manufacturing, quality assurance and FDA clearance regarding IPL.  I have researched numerous models and, as a result, have worked directly with five of these manufacturers as a consultant, service technician, technical writer and/or purchaser.

All this experience has given me a thorough understanding of the efficacy availed by modern IPL devices.

Desirable Features for IPL Devices –

Not all features are necessary for all types of procedures.  Some clinics need a simple IPL device to perform only a few functions such as PhotoFacials or acne treatment.  Sometimes this will be a second, less expensive, machine to fill in during busy periods.  Devices with fewer features tend to cost less to acquire and maintain, although that is not always the case.  Albeit, it is advisable for all practitioners to be aware of useful features and the benefits they provide.

Most of the features described herein involve technical aspects of light-based treatment.  It is not beyond the scope of a well trained practitioner.  The technologies avail substantial benefits to those who know how to use them.

Some marketing claims are superfluous, even though they may be trademarked or patented.  The features sound impressive but either lack the ability to produce a noticeable increase in efficacy, safety or profitability of treatment or they represent attempts to boost efficacy of an under-powered device.  Examples are “photon recycling” and heat-enhanced IPL such as Light-Heat Energy (LHE™).  These features will not be covered here but, if you are interested, feel free to contact me regarding my rationale for disregarding such technological claims.

Introduction – LASERs Have Dominated the Market

Due to their mono-chromatic properties (emitting only one wavelength), LASERs have been indicated for certain skin disorders via selective photothermolysis (the heating of selectively targeted tissue by particular wavelengths of light).  For example:

• Ultraviolet lasers (wavelengths shorter than 500 nm) have proven efficacy for the treatment of acne vulgaris due to the susceptibility of the P. acnes bacterium to those wavelengths.
• Pulsed Dye Laser (PDL) at 585 nm is particularly effective for targeting surface veins due to the high absorption coefficient of hemoglobin at that wavelength.
• Alexandrite lasers (755 nm) target melanin aggressively and are indicated for permanent hair reduction on lighter skin types and treatment of pigmented lesions (such as solar lentigines and port wine stains).
• Diode lasers (810 nm) are less aggressive on melanin than alexandrite lasers.  Consequently they have become popular for reduction of hair growth and vascular lesions on darker skin types.  Also, due to their simpler design, the total cost of ownership can be less than a traditional laser.
• Nd:YAG (1064 nm) lasers exhibit the deepest depth of penetration.  This makes them useful for treatment of deeper veins, deeper (thicker) hair follicles and hypo-dermal structures.  Due to a much lower absorption coefficient by melanin at this wavelength, they are indicated for treatments on the darkest skin types (even Fitzpatrick Type 6).

IPL – The Mainstay of a Profitable Medi-Spa

Intense Pulsed Light (IPL) devices have become one of the most important single pieces of equipment in the medi-spa practice.  The output of the mercury/xenon lamp (the standard flash lamp used for IPL) includes all the wavelengths from 400 nm to 1100 nm.  Newer IPL devices offer a level of power and sophistication to allow users to select many useful ranges of these wavelengths.  With proper optical filtration, wavelengths can be emitted for the specific treatments listed above.

IPL devices utilize high-pass (aka “low-cutoff”) filters that eliminate all wavelengths shorter than the stated wavelength.  For example, a filter (or handpiece) rated at 530 nm eliminates (blocks) all wavelengths shorter than 530 nm and passes all wavelengths longer than 530 nm.  When an IPL flashlamp, emitting light in a spectrum from 400 nm to 1100 nm, is placed behind a 530 nm filter the light emitted is a spectrum ranging from 530 nm to 1100 nm.

A 630 nm filter will eliminate more of the energy emitted by the flash lamp than a 530 nm filter.  Therefore, less energy is transmitted to the skin (and more energy is filtered off as excess heat in the handpiece) with a 640 nm filter than with a 530 nm filter.  (A 640 nm filter will emit a range of only 640 nm to 1100 nm.)

Longer wavelengths are very useful in aesthetic treatments.  However, many IPL devices do not generate enough power to permit the elimination of their shorter wavelength spectrum and still yield a clinical level of energy to the skin with the longer wavelengths.

Power – 

Judicious use of IPL relies upon using as little energy as possible to produce the desired endpoint (e.g. perifollicular edema for hair removal or localized erythema for vein reduction).  However, higher power IPL devices avail safer treatments.  Unit 8 of IPL Methodologies explains the details behind this counterintuitive observation.  The following is a brief summary of one of the more important points.

Consider treatments for reduction of hair, in-grown hair (pseudofolliculitis barbae, PFB), vascular lesions (telangiectasia, spider veins, hemangiomas, etc.), pore size or pigmented lesions (e.g. solar lentigines) on tanned or darker skin types.  For some of these cases longer wavelengths are indicated.

A filter of 530 nm is appropriate for certain treatments on lighter skin types (Fitzpatrick Types I-III).  If a patient presents a darker skin type or deeper depth of penetration of the energy is required (e.g. for deeper hair follicles, larger veins or more severe wrinkles) then longer wavelengths must be employed.  As longer wavelength filters are used (for example 640 nm, 690 nm or 750 nm) more of the output spectrum emitted by the flash lamp is eliminated.  An IPL device with limited power output cannot afford to have a large portion of its total spectrum of 400 nm – 1100 nm be eliminated and still emit sufficient energy to the skin.  IPL devices with high power flash lamps can afford to have a major portion of their output stripped away and still yield sufficient power to be emitted at the longer wavelengths.

A key component of the IPL device is the flash lamp.  High power flash lamps are more costly because they need higher gas pressure (requiring expensive sapphire/quartz instead of traditional glass), more sophisticated electrodes and more expensive manufacturing processes.

Higher power flash lamps generate more heat, requiring a more robust cooling system (larger pump, lines, valves and radiator).  Also, when longer wavelength filters are utilized, more of the emitted power is converted to heat as it is eliminated by the filter (in lieu of being transmitted to the skin).  This excess heat must also be carried away by the cooling system.

Higher power IPL devices also require larger power supplies and electrical components.  In summary, high power IPL devices are larger, heavier and costlier than their lower power competitors but avail substantially greater benefits for most types of IPL treatments.

Cooling System –

Low power IPL devices are generally air-cooled.  All powerful IPL devices are water cooled.  This is necessary to remove the heat generated by the higher power flash lamp and provide a satisfactory duty-cycle (the amount of time the machine can be operated before it needs to “rest” and cool off).  State-of-the-art machines have powerful sophisticated cooling systems  Modern IPL designs utilize high-pressure high-volume pumps to drive cooled water at high velocity through micro-channel ports to maximize cooling of the flash chamber.  Analogy can be drawn to automobiles.  All vehicles, old and new, utilize water cooling systems.  However, newer vehicles require higher-pressure cooling systems with special flow patterns to accommodate the newer high-compression (high heat) engines.

Higher powered IPL also generates more heat within the base unit due to the larger pumps, power supplies and other components.  Eliminating this “chassis-heat” requires larger fans (or dual fans) and proper thermodynamic design.

Larger, more expensive, cooling systems go hand-in-hand with more powerful IPL devices.  Some manufacturers boost power without boosting the cooling system, in an attempt to cut costs.  A key indicator of whether the cooling system is well matched to the power of the machine is the “duty cycle”.  A more robust cooling system will allow the practitioner to operate the device for longer periods of time before it needs to be powered down.  The resting or “cooling off” period can last 30 minutes or longer.  A longer duty-cycle allows more patients to be treated during the day.  More importantly, because machine shutdowns due to overheating always occur while it is in use, a longer duty-cycle minimizes embarrassing and costly rescheduling of appointments.  The duty-cycle is usually not stated in the spec sheets and it is often omitted in the User Manual.  However, the manufacturer knows this number.  It is to your advantage to know this vital statistic before you are caught by surprise in the middle of a procedure. 

External Filters – 

A convenient feature provided by some IPL devices is the ability to insert different filters into a single handpiece.  The alternative is to purchase an IPL device that employs different handpiece assemblies for different treatments.  The term “handpiece assembly” refers to the hand piece, the umbilical cable and the connector that plugs into the base unit of the IPL device.  The different handpieces all utilize identical flash lamps, circuitry and cooling technology.  The only difference is the filter that is integrated into them.  

It is easy to simply insert a filter for the desired treatment (430 nm for acne, 530 nm for vascular lesions, 560 nm or 630 nm for PhotoFacials, 690 nm or 750 nm for permanent hair removal, deeper vein reduction or collagen rejuvenation).  The alternative is to remove and insert different handpiece assemblies.  The trouble with exchanging handpieces is the difficulty in plugging the connectors into the base unit of the IPL device.  Exchanging handpiece assemblies is not easy and risks wear and tear on fragile O-rings.  

The O-rings (where the hand piece assembly connects to the base unit) are critical.  They need to be maintained in perfect condition to maintain a proper seal for the high-pressure water cooling lines.  Every time an O-ring is removed and reinserted, it risks additional scratches and tears on the rubber.  An O-ring failure can shut down a treatment room for days or weeks.

The difficulty in exchanging hand pieces should not be underestimated.  All handpieces are cumbersome to exchange due to the tight fit required to ensure complete sealing of the O-rings and proper electrical conduction in the high-voltage connections.  Consider hair removal or other treatments where regions of darker skin are encountered (e.g. areola, labial or tanned skin).  These treatment areas may require only a few pulses at a longer wavelength but will require the operator to swap out the entire hand piece assembly to treat a small area of skin.  Removal of the hand piece assembly and insertion of a different one will consume much more time than simply pulling out a filter and inserting one of a longer wavelength.  Furthermore, consider the patient who observes the difficulty with which the operator contends while struggling with the tight connector.  The ability to quickly swap filters will appear to be a more professional and competent procedure.

Manufacturers that produce different handpiece assemblies for different wavelengths generally do not offer as wide an array of wavelengths as those who offer external filters.  Integrated handpiece assemblies often come labeled as “AR” (acne reduction), “SR” (skin rejuvenation) and “HR” (hair removal) with no reference to the actual wavelengths emitted.  Operators that handle an array of filters, by necessity, must understand the advantages of the actual wavelengths and will generally get a much broader array of spectrums to use.

The final benefit is cost.  It is far less expensive to purchase one handpiece assembly and a box of filters than to acquire numerous handpieces.  It is beneficial to acquire a large treatment head, for treatment of large skin areas, and a small one for smaller areas such as facial features, bikini areas, etc.  Two handpiece assemblies (one with a large treatment crystal and one smaller) with a box of filters will accommodate all types of treatments.  Covering all those treatments with separate handpiece assemblies will require a larger outlay of funds.  Also, consider the office space required to store all the boxes, each containing a separate handpiece assembly.

Wide Array of Filters – 

It is intuitively obvious that a wider array of filters is more desirable than a lesser range of filters.  Some reasons evidencing this are explained below.  A wide choice of longer wavelengths is preferable.  A range of shorter wavelengths is also desirable.

Short wavelengths do not penetrate skin tissue as deeply as long wavelengths.  This can be used to advantage for the treatment of surface conditions such as rosacea, hematomas or pigmented lesions.

Acne vulgaris presents a unique situation for treatment.  Cystic acne can occur at relatively deep levels of the skin.  Transmission of light energy to these deep levels may require wavelengths longer than prescribed in the user manual.  Yet, treatment of P. Acnes bacterium in the sebaceous gland is best accomplished by use of a 400 nm or 430 nm filter.  (The sebaceous gland is shallow enough to be reached by these shorter wavelengths.)

Many IPL manufacturers offer an “Acne Treatment” (AT) handpiece; typically a spectrum filtration starting at 490 nm or 500 nm.  This range of energy will provide some beneficial results.  However, P. Acnes bacteria are particularly susceptible to wavelengths approximating 430 nm.  Filters that allow transmission at 430 nm (or shorter) provide significant efficacy.  The typical “Acne Treatment” (AT) filters of 490 nm or longer will not exhibit the same degree of efficacy.  

When presented by darker skin on different patients or patches of darker skin on the same patient, many operators will simply enter the new darker skin type into the display panel and the machine will adjust one or more of these parameters:

1. Energy Density – Fluence (Joules/cm2) will be reduced.
2. Pulse Duration – The pulse duration (pulse width) may be lengthened, applying the energy over a longer period of time, thereby reducing the total power (Energy/Time).  This is not always the case.  The device may shorten the pulse duration.  For critical details refer to the section: “Caution – Some Machines Do Not Adhere to the Formulas!”, pgs. 91-92, Vol. 1, IPL Methodologies).
3. Delay between pulses – If multiple-pulse (pulse train) mode is being used, the program may increase the delay between pulses.

Different machines are programmed by different engineers so the actual parameter adjustments will vary between models.  However, before any of these adjustments are made, the first parameter that should be changed is wavelength.  Choice of the proper wavelength is the major consideration; adjustment of the other parameters is merely “fine tuning”.

Longer wavelengths require more power.  Some models provide an array of filters with the longest wavelength at 640 nm or 690 nm.  The inability to offer a 750 nm (or longer) filter is an indication that the device does not emit sufficient power to operate in that useful range of the spectrum.

Super Hair Removal (SHR) – 

This is a design pioneered in 2006 by Alma Lasers, Inc. (US Offices: Buffalo Grove, IL; Corporate Headquarters Caesarea, Israel; subsidiary of Shanghai Fosun Pharmaceutical (Group) Co., Ltd., Shanghai, Peoples Republic of China).  It involves the emission of low energy density (fluences of less than 15J/cm2) applied at a rapid recovery rate (pulses emitted at a rate up to 10 Hz, a rate of 10 pulses per second) in a back-and-forth reciprocating motion over a small treatment area.  It has been touted as painless hair removal indicated for the reduction of any color of hair, including red, gray or white.

NOTE:  IPL devices citing SHR capability can still operate in traditional high power IPL mode.  No IPL devices are sold that provide SHR only.  The option to operate in SHR mode is generally offered as a choice at the first screen of the user interface.

SHR energy densities are extremely low compared to traditional treatments for permanent hair reduction.  IPL devices with high wavelength cut-offs (greater than or equal to 750 nm) or long-pulse Nd:YAG (1064 nm) lasers can often require energy densities of 40 Joules per square centimeter (40J/cm2) or more for traditional permanent hair reduction treatment depending upon the skin type, history of tanning, hair color, hair density and thickness.

I was very skeptical when trusted associates began touting the advantages of SHR to me in 2007.  It supposedly was painless permanent hair reduction that worked on all types of skin (Fitzpatrick Skin Types 1-6) and all types of hair (even gray and white).  I reasoned that these parameters could possibly show efficacy in shallow (fine/thin) dark-colored hair but how could it possibly work on deep hair or hair with no color?

Supporting literature claimed that applying numerous low-energy pulses would result in more energy being absorbed by the target chromophore than one high-energy pulse.  For example: if SHR pulses with a fluence of 10 J/cm2 are applied at a multiple-pulse rate of 10 Hz in a reciprocating motion over the treatment area, a total of 200 J/cm2 or greater might be applied to the target.  That is much more energy than a single pulse at 40 J/cm2 and will result in greater efficacy.  This simplistic explanation ignores important facets of Thermal Relaxation Time (TRT, the rate of heat loss by the chromophore after every pulse) and effective depth of penetration of the light energy.

Depth of penetration of light energy is a function of three variables:

1. Wavelength – longer wavelengths penetrate deeper
2. Spot Size (the area, in square centimeters) of a single pulse – larger spot size penetrates deeper than a smaller spot size
3. Energy Density – greater energy density transmits the light to a greater depth

How can SHR produce the same benefits for treatment of deep, thick hair follicles as traditional high-energy hair reduction protocols?  A series of low-energy pulses will not penetrate as deeply as one high-energy pulse (all other parameters being equal).  After experimenting with IPL devices capable of emitting light at SHR parameters, my initial skepticism was confirmed.  If you are targeting deep hair follicles (i.e. the thickest hair shafts), SHR will produce less permanent results.  In other words, hair regrowth will be substantial.

However, I was quite pleased to see that SHR parameters are adequate to effect permanent hair reduction of thinner hair (shallow hair follicles).  This is the hair that typically “survives” the initial two or three treatments conducted with traditional parameters (i.e. high energy, large spot size, low rep rate).  In other words, it works well when conducted during the third or forth and subsequent follow-up treatments (when the hair regrowth is thinner and appearing at a greatly retarded hair growth cycle).  The reason for this is the reduced Thermal Relaxation Time (TRT) of thinner hair vs. thicker hair.  (This is covered in detail in the classroom PowerPoint presentation.)

The ability to conduct the first two or three treatments in traditional IPL mode and then finish the treatment regimen in SHR mode is a wonderful option to offer to your clients.  Experienced hair removal practitioners will testify that the most painful treatments are the first two or three.  Subsequent treatments are generally less painful because:

1. The melanocytes (the target chromophores) are fewer in number per hair follicle.  This  is evidenced by the regrowth being lighter in color than the original hair.  This lower melanin density will build up less heat per centimeter of skin than the first two treatments where the hair follicles are at maximum melanin production.
2. The surviving hair follicles are located farther apart, as certain follicles are permanently disabled or severely retarded in their growth cycles.  This also generates less heat per square centimeter compared to the initial two treatments.
3. The surviving hair follicles are generally thinner in diameter.  This is evidenced by the regrowth being finer in texture than the original hair.  This allows the target chromophores to dissipate heat more quickly and easily.  

Third, fourth and subsequent treatments can utilize shorter pulse durations (to match the shorter TRT of the thinner targets) and greater number of “micro pulses” (to build up more heat in the target chromophores).  The SHR operating mode produces these parameters automatically.

Imagine being able to use only a fraction of the initial energy settings to effect similar efficacy.  Subsequent treatments need not be “less painful” they can be almost pain-free!  This is a nice benefit of IPL devices that can provide SHR.

SHR capability is integrally linked to Optimal Pulse Technology (OPT) outlined below.  OPT is the true key to providing SHR as well as multiple-pulse capability, as will also be covered below.

Regardless of fantastic claims of permanent reduction of all types of hair, one aspect of SHR aroused my interest when I first heard about it.  It was the parameters that could now be achieved by IPL.  I provided input to research conducted in 2000 regarding LaserGenesis.  This is a procedure using long-pulse Nd:YAG laser emitted at low fluences (8-14 J/cm2) over high pulse rates  of 5 – 10 Hz.  It is pulsed over the treatment area in a rapid back-and-forth manner, similar to that of SHR.  The endpoint of this treatment is not to disable hair follicles but, rather, to gently build up a slight heat differential (only a few degrees over normal skin temperature) that induces fibroblasts to “wake up” and produce new collagen (neocollagenesis).

This is a truly painless way to reduce deep wrinkles and tighten lax skin.  IPL devices produce a large amount of light in the range of 900 nm to 1100 nm.   The trick to using this very beneficial range of wavelengths is to possess an IPL capable of producing enough power so that you can filter off all the shorter wavelengths and still have enough energy to emit only the longer wavelengths.  Few IPL devices offer a cut-off filter as high as 750 nm.  This aspect was discussed above in the section titled “Power”.  For a complete explanation, refer to the section in IPL Methodologies titled “Issues Affecting Use of IPL Filters”.

The key to LaserGenesis is to be able to maintain consistent energy levels as the device is used in a rapid multiple-pulse mode.  The energy levels of pulses subsequent to the initial one in a typical multiple-pulse IPL tend to decrease substantially.  This is very detrimental for LaserGenesis.  The problem with decreasing energy levels is solved by Optimal Pulse Technology (OPT).  OPT is outlined below.

The detailed protocols for the LaserGenesis procedure are beyond the scope of this paper.  In summary, I used IPL devices capable of operating at SHR parameters (low energy, long wavelengths and multiple pulses at high rep rates) and achieved results comparable to that of LaserGenesis.  A regimen of five or six treatments, conducted at intervals of four to six weeks, achieved a significant reduction of wrinkles, tightening of lax skin, reduction of vascular and pigmented lesions as well as a marked improvement in skin texture.  It is a pain-free and relaxing procedure that is well tolerated by patients.

Not all patients respond equally to this procedure.  However, most will exhibit benefits approaching those of PhotoFacial treatment, i.e. reduced pore size, reduced dyschromia and reduced skin laxity and rhytides.  A key benefit is that these results can be produced while avoiding the risks associated with the high energies and shorter wavelengths of PhotoFacial parameters.

In summary, the SHR feature tends to be overly touted for hair removal but it provides a definite benefit to your practice.

Foot Pedal Option – 

The option to initiate the light pulse via foot pedal instead of a button on the handpiece has been available for a long time on many IPL models.  Although it would appear to be advantageous, this option has not been widely used by operators in traditional IPL treatments.  This is because of the importance of properly aligning each pulse to be contiguous to the prior one with a very slight over-lap.  This requires focused concentration and accuracy in placing every new pulse.  Using a foot pedal can increase the chances of emitting a pulse before proper alignment or skin contact is achieved.

With the advent of SHR, where the treatment surface (the “light guide” or “crystal”) is moved rapidly across the skin while the handpiece button is continually depressed, the ability to keep your foot on a pedal switch will minimize fatigue in your thumb or “trigger finger”.

Multiple Pulsing (“Pulse-Train”) –

This is the ability to emit two or more rapid pulses out of the handpiece for every “push of the button”.  Multiple pulsing has been shown to produce benefits in ramping-up the temperature of the target chromophores in relation to surrounding competing chromophores.  The endpoint temperature of the desired chromophore can be maximized via repeat pulsing, exceeding the temperature attainable by a single pulse, thereby ensuring maximum efficacy.  While this is being done, the heat in the non-targeted tissue is also rising but to a lower endpoint temperature.  Even though the Thermal Relaxation Time (TRT) of the non-targeted tissue may be similar to that of the target, the endpoint (post-pulse) temperatures of the targeted and non-targeted tissue will diverge during a train of rapid pulses.  If the TRT of the non-targeted tissue is less than that of the target, (the case with thicker veins or hair follicles) the temperature divergence will be even greater.

Because of the clinical evidence, almost all high-powered IPL devices offer this feature.  (Low-power IPL devices cannot retain sufficient electrical energy in their capacitors to emit more than one pulse before requiring a “recharge”.)  On some high-power IPL devices, a push of the button (or foot pedal) can be programmed to emit as many as ten or fifteen pulses from the flash lamp.  This can be confusing to a new practitioner.  If two pulses are better than one and three pulses are better than two, are ten pulses better than nine?

There is an abundance of clinical research that evidences the benefit of two or three multiple pulses to that of a single pulse.  (This is detailed in the graphs displayed in the classroom PowerPoint presentation.)  I have been unable to locate any research conducted on the benefits of five, seven, nine or more pulses.  Marketing allure has now taken effect.  If two pulses are good and three are better, then ten (or some other high number) must be best.

A major problem with using multiple pulses is that traditional IPL designs cannot maintain a constant level of energy for all the pulses.  The energy tends to decline after the first “mini-pulse” or “emitted pulse”.  For example, if the device is programmed to emit three pulses at 20 J/cm2, the first pulse will be 20 J/cm2 but the second may be 17 J/cm2 and the third may only be 14 J/cm2.  This is because the electrical capacitors, devices that store and release the electric power needed to fire the flash lamp, lose some of their electrical charge after each pulse.  If the energy level of subsequent pulses decreases, the benefits attainable by multiple-pulsing are diminished.

The speed at which the capacitors can recharge to a proper voltage is called the “recovery rate” (measured in Hz, pulses per second).  This is the maximum rate at which a single pulse or a series of mini-pulses can be emitted by the device.  Low power devices often operate at a maximum recovery rate of 0.5 Hz or lower.  That means the device requires 2 seconds (in the case of a 0.5 Hz recovery rate) to recharge the capacitors after every “treatment pulse” (push of the button).  High power IPL devices utilize large power supplies that can quickly recharge the capacitors.  These machines often can fire at a rate of 2 Hz (one pulse or one pulse-train every 0.5 second).

The recovery rate of the device is different than the maximum number of multiple pulses.  In multiple-pulsing the capacitors are charged once (same as a single pulse) and then emit their electrical power in a measured amount for each of the emitted pulses (“mini-pulses”) before recharging.  With traditional IPL design, this requires each subsequent mini-pulse to be emitted at slightly less energy than the previous one.

As an analogy, imagine a bucket filled with water and fitted with a spigot at the bottom.  The bucket represents the capacitor and the water represents potential electrical energy (voltage).  Each time the valve is opened the water flows out with a certain level of kinetic (moving) energy and the remaining water level decreases.  As the water level drops, the force of the water emitted by subsequent releases will decrease.  If the bucket is almost empty, the water will barely trickle out of the spigot.  This is what happens if too many multiple-pulses are programmed into the IPL device.  After several “mini-pulses” the energy level will drop tremendously.  It raises serious doubts about the efficacy of five, ten or more multiple pulses.

This phenomenon is addressed by a newer design that is often called “Optimal Pulse Technology” (OPT).  OPT circuits, if properly employed, can allow multiple-pulses to be emitted at a substantially equal level.   This is discussed in the next section below.

OPT – 

The term OPT has become ambiguous.  That is because it can represent different technologies:

1. OPT may refer to Optimum Pulse Technology – This often refers to the shape of the pulse (pulse formation), explained below under “Top Hat” Pulse Profile.  However it can refer to the technology described in #2.
2. OPT may refer to Optimal Pulse Train – This refers to the ability of the IPL device to emit a train of pulses (multiple pulses) that are substantially equal in energy.

“Optimum Pulse Technology” refers to the shape of the electrical pulse sent to the flash lamp.  “Optimal Pulse Train” refers to the energy level of each pulse.  The term OPT is well worth investigating, either with a well informed sales rep or a design engineer back at home office.  If the manufacturer touts OPT it means that they are attempting to do something to keep up with technological advances.  It takes some inquiry to figure out exactly what they are offering.  If they say OPT results in a less painful treatment then they are probably referring to definition #1 above.  If they say OPT avails greater efficacy then they are probably referring to definition #2.  The remainder of this section will refer to #2, the ability of the device to maintain a substantially consistent energy level while emitting a series of pulse trains.

One way that energy drain can be reduced between multiple pulses is to utilize better and larger electrical capacitors.  Capacitors represent a substantial portion of the manufacturing cost.  Higher grade and larger capacitors increase the cost of the machine significantly and add to the total weight and bulk of the device.  These drawbacks are unavoidable but provide for significantly better performance.

OPT involves more technology than simply bigger and better capacitors, the scope of which is beyond that of this paper.  An important thing to realize is that it is economically unfeasible to make an IPL device that emits a pulse train of perfectly equal energy.  OPT technology represents a cost-effective way to ensure that energy losses during the pulse train are minimized.  A device with OPT will exhibit greater efficacy than one lacking OPT.  Without OPT, the benefits of multiple pulsing will be limited.

“Top Hat” Pulse Profile –

Top Hat means that the shape of the pulse of light, when plotted on a graph showing energy on the Y-axis and time on the X-axis, represents the shape of a “top hat” such as worn by Abraham Lincoln and other prominent citizens in the 19th century.

The following represents a typical “Top Hat” claim:

This graph represents a pulse emitted at a certain amount of energy over a duration of 10 ms (ten milliseconds, ten thousandths of a second).  You can see how the shape of the pulse is similar to that of a top hat.

But how can a light beam emit a certain amount of energy and zero energy at the same point in time (the vertical sides of the hat)?  It can not!  The light energy must take some amount of time to reach its programmed level.  This is the time required to discharge the electrical capacitors, energize the gases in the flash lamp and emit the resulting light out of the handpiece.  Furthermore, after the desired amount of emission time is achieved (in the above case, 10ms), the IPL device must then turn off the power to the flash lamp and the gases must stop emitting the light.  The power-up and power-down cycles take some time to accomplish, electrically (via the control circuitry and capacitors) and chemically (via the mercury/xenon gases in the flash lamp).  Therefore, a true “Top Hat” pulse profile is impossible to achieve, although it is often touted in marketing literature.

The following is a graph of a real pulse of intense light.