Intense pulsed light
‘Intense pulsed light (IPL) or flashlamp is a form of light-based hair removal.
Some consumers have experienced permanent hair reduction, but there is limited data on how much hair reduction is typical, and how often hair reduction occurs.
Full spectrum (non-coherent) light and low-range infrared radiation are filtered to allow a specified range of wavelengths.
This filtered light is delivered from a handpiece into the skin, where it targets dark material such as the pigment in hair.
This is intended to cause thermal and/or mechanical damage to a hair follicle while sparing surrounding tissues.
Some consumers have experienced long-lasting hair removal or permanent hair reduction.
Considered safe if performed properly.
Useful for large areas such as backs or legs.
Regrowth can come back lighter in color or finer in texture.
Light-skinned consumers with dark hair have the best results.
Long-term data on safety and effectiveness have not been established.
Response rates have not been established.
Not as effective on unpigmented hairs and red or blonde hair.
Must be used very cautiously on darker skin tones or on consumers who tan themselves.
Improper treatment can cause burns, skin discoloration lasting several months, or patchy/grid-like regrowth.
Requires eye protection.
Can be expensive.
Some find treatment painful.
Regulation varies by state, so inadequate controls exist to ensure competent practitioners.
Some consumers do not respond to treatment.
"Painless" or "virtually painless"
While many clients tolerate flashlamp without requiring pain relief, it's overpromise to state that treatment will be painless for all consumers.
"Permanent hair removal" or "100% permanent" or "permanent"
Some consumers experience permanent reduction of treated hair over the course of treatment, but published studies have observed that many consumers are not good candidates, and even ideal candidates with light skin and dark hair do not always respond to treatment.
"Guaranteed 0% regrowth"
There is no published clinical data to substantiate this sort of overpromise.
This marketing term suggests that flashlamp is better than laser for consumers, but this is not always the case.
Also called IPL (intense pulsed light), ILS (intense light source), full spectrum, non-coherent, and broadband light. The primary differences between flashlamps and lasers used in hair removal are:
Kind of light
As mentioned earlier, flash lamps do not use one wavelength of light the way a laser does. Flashlamps emit every wavelength of light in the visible spectrum, and a little into the band of infrared radiation (up to about 1200 nm). Practitioners select a cutoff filter to block out lower wavelengths.
Size and shape of the spot (beam)
Most flashlamps emit a beam that covers more area than a laser. Most flashlamps also have a rectangular spot, rather than the round type usually standard on lasers.
Xenon is commonly used as a light source because of the brilliant, full spectrum illumination it provides when exposed to energy. Like laser, it can be designed to be extremely powerful and has industrial applications like paint stripping. It is also used for items such as the flashes in photographic equipment and in surgical lighting equipment.
The xenon flashlamp, first developed as an energy source for laser beams, was soon being used therapeutically with direct applications of its energy. As with lasers, flash lamps began to be used for medical purposes in the 1960’s. The latter half of the 1960’s saw published data on treating eye and skin disorders. [1, 2]
Early attempts in the 1970’s to use xenon light energy delivered via fiberoptic filament have not been demonstrated to be permanent. Although these devices (see photoepilators) are still in use, they should not be confused with the devices that became available 25 years later.
By the mid-1990’s, researchers were exploring the use of flashlamps for treating vascular lesions. In the year the first flashlamp was cleared by FDA for use in treating vascular lesions,  one study noted hair loss as a side effect of treatment.  Other papers indicated promising results for some in the treatment of leg veins, [5, 6] prompting one manufacturer to apply for and receive FDA clearance for hair removal in 1997.  In 2000, FDA began allowing some brands to claim permanent hair reduction in most skin types.  The darkest skin type was not included.
There is limited clinical data and even less with long-term follow-up for flashlamps.  Arguably the best overview is Tse.  Several brief discussions suggest usefulness without detailing clinical data. [11, 12, 13, 14, 15]
The pilot study observed 60% reduction at 3 months  and 75% at 12 months.  Another study observed 80% reduction at 8 months.  One study with no follow-up observed 77% reduction immediately after a 6th treatment. 
Two articles reporting on overlapping patient groups reported 54% to 64% reduction at 6 months. A later study by the same authors observed 76% reduction immediately after a 4th treatment.  The study observed 41% of subjects had an average 83% reduction at 12 months or more. 
One clinical report found “satisfactory” results at 6 months in 2 transsexuals who received 13 and 41 treatments, respectively.  Another clinical report observed one patient had successful removal of transplanted scalp hair grafts with 1.5 year follow-up. 
One study had findings which aligned more closely with other reported light-based results, observing an average 33% reduction at 6 months after 2 treatments. 
Laser and flashlamp promoters sometimes suggest the devices are very different in terms of effectiveness or side effects, but this is not based on published comparative data.
1. Verhagen AR. Light tests and pathogenetic wavelengths in chronic polymorphous light dermatosis. Dermatologica. 1966;133(4):302-12. 2. L'Esperance FA Jr. Clinical comparison of xenon-arc and laser photocoagulation of retinal lesions. Archives of Ophthalmology. 1966 Jan;75(1):61-7. 3. FDA Docket K950493. August 7 1995. 4. Hellwig S, Schonermark M, Raulin C.[Treatment of vascular malformations and pigment disorders of the face and neck by pulsed dye laser, Photoderm VL and Q-switched ruby laser].Laryngorhinootologie. 1995 Oct;74(10):635-41. German. 5. Goldman MP, Eckhouse S. Photothermal sclerosis of leg veins. ESC Medical Systems, LTD Photoderm VL Cooperative Study Group. Dermatologic Surgery. 1996 Apr;22(4):323-30. 6. Schroeter CA, Neumann HA. An intense light source. The photoderm VL-flashlamp as a new treatment possibility for vascular skin lesions. Dermatologic Surgery. 1998 Jul;24(7):743-8. 7. FDA Docket K963249. July 7, 1997. 8. FDA Docket K991935. January 27, 2000. 9. Please see hairfacts.com for a list of the flashlamp medical literature. 10. Tse Y. Hair removal using a pulsed-intense light source. Dermatologic Clinics. 1999 Apr;17(2):373-85, ix. 11. Fitzpatrick RF Goldman MP Sriprachyaanut S. Hair removal utilizing the ESC Epilight device. Lasers in Surgery and Medicine (supplement) 9 36:1997. 12. Smith SR, Tse Y, Adsit SK et. al.Long-term results of hair photo-epilation. Lasers in Surgery and Medicine (supplement) 43:1998. 13. Gold MH. Hair removal with an intense pulsed-light source. Lasers in Surgery and Medicine (supplement) 10 58:1998 14. Weiss G, Cohen B. The efficacy of long-term epilation of unwanted hair by noncoherent filtered flashlamp. Lasers in Surgery and Medicine. 2000;26(4):345. 15. Weir VM, Woo TY. Photo-assisted epilation: review and personal observations. Journal of Cutaneous Laser Therapy. 1999;1:135-143. PMID not available. 16. Gold MH, Bell MW, Foster TD, Street S. Long-term epilation using the EpiLight broad band, intense pulsed light hair removal system. Dermatologic Surgery. 1997 Oct;23(10):909-13. 17. Gold MH, Bell MW, Foster TD, Street S. One year follow-up using an intense pulsed light source for long-term hair removal. Journal of Cutaneous Laser Therapy. 1999;1:167-171. PMID not available. 18. Trollius A, Troillus C. Hair removal with a second-generation broad spectrum intense pulsed light source: a long-term follow-up. Journal of Cutaneous Laser Therapy 1999;1:173-178. PMID not available. 19. Schroeter CA,and others. Hair removal in 40 hirsute women with an intense laser-like light source. European Journal of Dermatology. 1999 Jul-Aug;9(5):374-9. 20. Sadick NS, and others. Available Long-term photoepilation using a broad-spectrum intense pulsed light source. Archives of Dermatology. 2000 Nov;136(11):1336-40. PMID 11074695 21. Sadick NS, Shea CR, Burchette JL Jr, Prieto VG. High-intensity flashlamp photoepilation: a clinical, histological, and mechanistic study in human skin. Archives of Dermatology. 1999 Jun;135(6):668-76. 22. Raulin C, Werner S, Hartschuh W, Schonermark MP Effective treatment of hypertrichosis with pulsed light: a report of two cases. Annals of Plastic Surgery 1997 Aug;39(2):169-73 PMID 9262770 23. Moreno-Arias GA, Navarra E, Vilalta A, Ferrando J. Corrective photoepilation for improper hairline placement after hair transplantation. Dermatologic Surgery. 2000 Aug;26(8):790-2; discussion 792. 24. Weiss RA, Weiss MA, Marwaha S, Harrington AC. Hair removal with a non-coherent filtered flashlamp intense pulsed light source. Lasers in Surgery and Medicine. 1999;24(2):128-32.