First, the principle of intense pulsed light Intense pulsed light, referred to as intense light, also known as photons, is a kind of high-energy xenon flash lamp released under the action of tens of thousands of volts of high voltage polychromatic pulsed light source. Intense pulsed light consists of non-coherent, non-parallel broad-spectrum light with wavelengths usually ranging from 400 to 1200 nm, and therefore is not strictly a laser. Photon is mainly used for the treatment of skin aging, in addition to which it is also widely used for the treatment of various pigmented skin diseases, vascular skin diseases, hirsutism and even inflammatory skin diseases (e.g. acne and rosacea). Intense pulsed photodynamic therapy (PDT) with a combination of photosensitizers (e.g., 5-aminoketovaleric acid) has also become an effective treatment for photoaging and severe acne. Like laser, the mechanism of action of PDT is based on the principle of selectivephotothermolysis. There are various target chromophores such as melanin, hemoglobin and water in the skin. Different target chromophores absorb light at different levels: melanin absorbs less light with increasing wavelength in the range of 290-1200 nm; hemoglobin has three absorption peaks of 418 nm, 542 nm and 577 nm; water absorbs mainly in the near-infrared band. Strong pulse light as a broad-spectrum light, its wavelength range basically covers the main absorption peak of the above target chromophores, so through the filter to choose a wavelength more easily absorbed by the target chromophores, and by adjusting the pulse width to make it shorter than the thermal relaxation time of the target chromophores, under the action of sufficient energy, with a reasonable pulse interval and simultaneous cooling, it can effectively and safely destroy the skin lesions, to achieve the purpose of cosmetic treatment. Second, the difference between the equipment of intense pulsed light The development of intense pulsed light has a history of more than 20 years, with the continuous progress of photon technology, different equipment manufacturers have introduced 30 kinds of intense pulsed light systems, most of which have multiple sub-pulse mode, uniform pulse, multi-filter combination, synchronous cooling, large treatment hand and high energy output and other characteristics. In order to achieve optimal efficacy and reduce adverse reactions, it is important to master the technical parameters such as filters, pulse width, pulse interval, cooling mode and energy density. Most intense pulsed light devices emit multicolor broad-spectrum light of 400-1200nm wavelengths, and specific wavelengths are selected for treatment by using dichroic filters. The filter can remove the light below its calibrated wavelength. If a 560nm filter is used, the output light has a spectral range of 560-1200nm. The main filters used in clinical practice include 515nm, 550nm, 560nm, 590nm, 615nm, 640nm, 645nm, 695nm and 75nm. Some devices provide 420nm filters for the treatment of acne, or even UV band intense light for vitiligo, etc. Intense pulsed light of different wavelength ranges can be absorbed by hemoglobin, pigment and water to treat blood vessels of different sizes and depths, pigment-based diseases and stimulate collagen growth. Most current intense pulsed light devices offer adjustable multiple pulse widths (0.5-90ms) and sub-pulse modes (single or multiple sub-pulses) to target chromophores with different thermal relaxation times, but there are significant differences between devices. The pulse interval, or pulse delay, is the time interval between sub-pulses and is usually adjustable between 1 and 300ms. The pulse interval of photonic devices using intelligent pulse mode is generally controlled by the master computer. For darker skin tones, longer pulse intervals help protect the epidermis and reduce adverse reactions. Simultaneous cooling is an important aspect of the safety of photonic devices, especially for darker skin tones, reducing pain and the risk of erythema and blister formation. Most photonics devices use synchronized cooling with cold circulating water adjustable from 5-25°C. In addition, the treatment handpiece of a photon device generally has a large rectangular treatment head with a skin contact area of up to 25 cm2, allowing a wide range of treatments, such as the full face and extremities, to be completed quickly. The energy output of photon devices is measured in terms of the radiation received per unit area, i.e., energy density (in J/cm2). The energy density setting (3 to 90 J/cm2) varies among different brands of photon devices; the same energy density is not common across different brands of photon devices. For each patient’s treatment, the choice of energy density requires consideration of various factors such as Fitzpatrick’s skin type, the nature of the lesion, the location and the response of the test spot. Tip: What are the differences between IPL and laser treatment? The main difference between IPL and laser treatment is that laser is a monochromatic, coherent light source and therefore highly selective and destructive to a single target chromophore, while IPL is a polychromatic, non-coherent light source and is less destructive to a single target chromophore than laser, but can simultaneously target multiple target chromophores such as pigment, blood vessels and water, and is therefore more advantageous for complex lesions.