Which brand of home use IPL hair removal device is better?
The detailed technical parameters of more than 30 hair removal instruments were sorted out in this article.
Basis of determination: literatures, energy measured video of several hair removal device I updated, measured filter distribution map, measured pulse waveform, FDA official website, feedbacks from readers over the past few years, personal using experience of several hair removal devices and the instructions of these hair removal devices.
I almost saw all the literatures about home use devices. Some problems of Silkn had been pointed out by some literatures  are short wavelength and low energy, which may cause eyes risks, unnecessary skin absorbed and temporary effect. And it had a clear uneven distribution of energy where the energy is concentrated in an area off-centre of the treatment area. You can see it in the following figure.
Problems with some hair removal devices which are presented by literatures
In the domestic market of China, sales by brand marketing and prices, and about the effect of technology is always be despised. Because hair removal device has temporary effect but the long-term effect is diffcult to compare. Silkn has new models, but the core parameters, such as 475nm filtering and energy density, are the same as they were more than a decade ago.
What effect can hair removal device achieve?
Permanent hair removal: most of hair follicles have been destroyed after a year of hair removing treatment, and most hair will not regrow in few years after the treatment. The professional effect of hair removal.
Tempororily growth delay: most of hair follicles are not destroyed, but they can from growing stage into dormancy, there will be a temporarily growth delay. The delay effect may be reversible and the hair will regrow without a long time. Home use hair removal device with low energy falls into this category. Only a few of home use hair removal devices can achieve permanent hair removal.
That is why the technical parameters of internet celebrity devices is not good enough but the feedback is effective. In theory, it can be done to temporarily growth delay but the effect persistance and security is uncertain. The product is good or bad, it needs to compared with other similar products. Otherwise, I can freely praise every product. Only talking about the brand story and the origin of the product without talking about itself, It is the same as the recommendation idea of internet celebrities. Only the technical parameters can be quantified and compared, it is an important basis to judge the safety and effect: wavelength, energy, light area, pulse width.
Hair removal filter
Domestic hair removal device mainly use Intense Pulsed Light(Intense Pulsed Light =photon=IPL). The wavelength is used to filter the harmful and invalid short wavelength, for example, the 475nm wavelength is used to get the IPL filter of 475-1200nm. Many home use IPL have short wavelength which are high risks to skin and eyes. Selecting an appropriate wavelength of hair removal device, can safety hair removal, and this is the basis of improving the effect of hair removal.
Penetration depth comparison of hair removal filter
The wavelength determines the accuracy of light effect, that is security. The weak wavelength should be eliminated ignore the power level. Most of hair removal devices have short wavelength and lack of penetration, it is difficult to targeted at the root of hair follicles and the energy is mainly obsorbed by the epidermis and blood which causes low security. There is a high risk of hair removal for dark skin. Improper operation may cause blisters, pigmentation and scarring. Only when the wavelength is appropriate, the light can be selectively absorbed by the hair follicle but not by the epidermis and blood. With the maximum utilization and without unnecessary impact on other tissues.
According to the theory, clinical experience and the Guidelines for Technical Review of The Registration of Intense Pulsed Light Therapeutic Devices formulated by CFDA, the 590-650nm wavelength of filter is suitable for professional IPL hair removal device.
IPL with too short wavelength can not accurately act on hair follicles and stimulate skin, so the energy can not be high, which will affect the effect. Moreover, short wavelength is also difficult to be effective when taking off deep-rooted parts such as armpits. On the contrary, long wavelength IPL red light can be safely absorbed by hair, such as Stylight and Sheermate, which can set higher energy to improve the effect and not easy to hurt the skin.（while protecting the skin）
The relation between the wavelength and color of filters of each IPL device
Different wavelengths of IPL can be reflected in different colors of filters. The hair removal device with short wavelength is not recommended. It is yellow filter, such as Smoothskin, Braun, Philip SC19 and BRI86 series, Ulike sapphire, Lescolton, Deess, Konka and Silkn etc.
Studies have shown that short wavelength IPL has risks to the eyes. Once blue-green light (470-530nm) is transmitted to the eyes and absorbed by retinal pigment, it may cause permanent eyes injury.
However, it can not just look at the parameter data in the instruction. The wavelength should be combined with the color of the flash lamp cap. For marketing, some salers will modify the parameter of product instead of inproving it: Smoothskin and Braun, these two products are the same. It is saled in China that the filter is 610-950nm, which is inconsistent with the 510nm filter on FDA. The yellow filter on the lamp cap confirms the fact of 510nm wavelength. Actually, Pure, Muse and Braun energy density 6J/ cm² is just suitable for white skin, the darker the skin color, the lower the energy.
The color of filters of different filter
Summary: IPL hair removal device selects 590-650nm red filter (above 590-1200nm), which has the best hair removal effect and safety in clinic and theory, e.g. Stylight, Sheermate and Amiro with red filters.
Hair removal energy
The higher the energy and the energy density, the more persistant the hair removal effect. The higher the total energy, the deeper the penetration of light and the more evenly distributed. Most of home use hair removal devices have low energy that cause a temporarily delay in hair growth, but they can't destroy hair follicles and remove hair for a long time. So, it is hard to compare the long-term effect or the temporary domancy according to the various of assessments and the buyers comments because they only use the devices for a few months. Most of the pictures do not tell us how many days and how many times since the last time they use the devices. It is lack of reference value.
Research shows that at least 5J/cm² energy density is required to damage hair follicles, prevent hair regeneration and achieve long-term hair removal effect. When the pulse width and the wavelength is suitable, the higher the energy, the greater the damage to hair follicles, the longer the hair removal effect and the more abvious the pain.
The energy is the easiest of fake indication. I measured the energy value of the popular and high energy products on the market by using the Israel OPHIR power meter.
The maximum energy is Sheermate that reaches 30J and the energy density is 7.5J/cm², it is safer with red filter. And it's a desktop model, so the energy can be set higher.
Smoothskin: the power mode of Pure only has 7.5J/cm² on the white skin, but it is easy to obsorbed by the epidermis and blood because of the short wavelength (the color of the filter is yellow). Therefore, the energy level can only be seleted according to the skin color(the energy of dark skin color is lower) but can not adjusted by youself. It has high risk to set the energy high for dark skin color. Bare puls is a typical example of exchanging effect for convenience, which halve the energy to 4J/cm², double the speed and reduce the volume. It reflects a trend of despising effect and emphasizing on experience.
Ulike: the wavelength is short. And the ice cooling is almost useless because the energy only can reach 4.8J/cm². It is better to focus on increasing the energy and wavelength.
Refute a rumor: Is the higher the energy, the greater the stimulation to the skin? No, the security is related to the wavelength of filter. The wavelength of the high-energy device itself should be safer (above 590nm filter) in order to set the energy higher. It is recommended to choose high energy and use it with ice pack if you afraid of pain but want best effect and the better part of pain can be reduced after ice compressing.
The energy is large, the painful is obvious or needs ice compressing, and the flash speed is lower. Single operation is time-consuming, but the effect is good. On the contrary, it needs to be used every 3 days in the early stage and concentrated frequently use because of the low energy of the hair removal device. Due to it can not destroy hair follicles, it should continue to used after a year. In this way, it is really a kind of damage and frequent stimulation to the skin. In the long term, the total time of using a high energy hair removal device is shorter than low energy devices.