The critical function of cut-off filters ranging from 615nm to 755nm in Intense Pulsed Light (IPL) systems is to selectively block shorter wavelengths (blue and green light) that are highly absorbed by the epidermis. By filtering out light below these specific thresholds, the equipment permits only longer wavelengths to pass through, enabling deep penetration into the dermis to target hair follicles while significantly reducing thermal damage to the skin's surface.
Core Takeaway The range of 615nm to 755nm serves as a "safety gate" for darker skin types and deep targets. By eliminating surface-absorbed energy, these filters shift the optical focus from the epidermis to the deep dermis, minimizing the risk of burns and post-inflammatory hyperpigmentation (PIH) during hair removal.
The Mechanism of Spectral Selectivity
How Cut-off Filters Function
IPL utilizes a xenon flashlamp that naturally generates a broad spectrum of light (polychromatic). A cut-off filter, often embedded in the sapphire light guide, acts as a barrier that blocks all wavelengths shorter than the filter's specific number (e.g., a 645nm filter blocks everything below 645nm).
Eliminating Competitive Absorption
The epidermis is rich in melanin, which eagerly absorbs shorter wavelengths (blue and green light). If these wavelengths are not filtered out, the surface melanin absorbs the energy before it can reach the target. Filters in the 615–755nm range remove this "competitive absorption," preventing the epidermis from overheating.
Maximizing Depth of Penetration
Longer wavelengths have a physics advantage: they travel deeper into human tissue. By restricting the output to the 615nm–1200nm range (depending on the specific filter used), the system forces the light to bypass the surface and deposit its energy into deep structures, such as the hair bulb.
Clinical Safety and Skin Type Adaptation
Protecting Epidermal Melanin
The primary safety challenge in IPL is treating patients with higher Fitzpatrick skin types (darker skin). These patients have high concentrations of epidermal melanin. Using filters in the higher range (690nm or 755nm) effectively "blindfolds" the light to the surface pigment, allowing safe passage through darker skin.
Reducing Post-Inflammatory Hyperpigmentation (PIH)
When surface melanin absorbs too much heat, it can lead to burns or PIH (dark spots caused by inflammation). By strictly filtering out the highly absorbable shorter waves, 615–755nm filters act as a core hardware safeguard against these complications.
Selective Photothermolysis
This filtration enables true "selective photothermolysis." It ensures the destruction is confined to the specific target (the dark hair follicle) without collateral damage to the surrounding tissue, specifically the pigmented epidermis.
Understanding the Trade-offs
Reduced Efficacy on Superficial Targets
While 615–755nm filters are excellent for deep hair removal, they are ineffective for treating superficial issues. Conditions like surface sun spots, freckles, or superficial telangiectasia (spider veins) require shorter wavelengths (515nm–590nm) for effective absorption. Using a 755nm filter on a surface freckle will likely yield poor results because the light penetrates too deeply to heat the lesion.
Higher Fluence Requirements
Because melanin absorption decreases as wavelength increases, you may need to adjust energy settings. However, the safety margin provided by these filters generally allows for effective treatment parameters without compromising skin integrity.
Making the Right Choice for Your Goal
To maximize the utility of your IPL equipment, select filters based on the depth of the target and the patient's skin color:
- If your primary focus is Hair Removal on Darker Skin (Fitzpatrick IV-VI): Utilize higher cut-off filters (690nm or 755nm) to bypass epidermal melanin and safely target deep hair follicles.
- If your primary focus is Hair Removal on Lighter Skin (Fitzpatrick I-III): A 615nm or 645nm filter provides a balance of melanin absorption and depth, offering effective treatment for deeply rooted hair.
- If your primary focus is Superficial Pigmentation or Vascular Lesions: Do not use the 615-755nm range; switch to lower cut-off filters (515-590nm) to target surface chromophores.
The correct filter selection transforms a single IPL device from a surface-level skin rejuvenator into a deep-targeting, safety-focused hair removal tool.
Summary Table:
| Filter Wavelength | Primary Target | Ideal Skin Type (Fitzpatrick) | Main Clinical Benefit |
|---|---|---|---|
| 615nm - 645nm | Deep Hair Follicles | Types I - III | Balanced absorption for effective hair removal on light skin |
| 690nm - 755nm | Deep Roots / Darker Skin | Types IV - VI | Maximum epidermal safety; minimizes risk of burns and PIH |
| Mechanism | Spectral Selectivity | All compatible types | Blocks shorter waves to prevent surface melanin overheating |
Elevate Your Clinic’s Treatment Safety with BELIS Technology
Precision filtration is the difference between superior results and accidental complications. BELIS specializes in professional-grade medical aesthetic equipment designed exclusively for clinics and premium salons. Our advanced IPL and laser systems—including Diode Hair Removal, CO2 Fractional, and Pico lasers—incorporate high-end sapphire light guides and precision cut-off filters to ensure maximum patient safety and clinical efficacy.
Whether you are looking to expand your services with HIFU, Microneedle RF, or body sculpting solutions like EMSlim and Cryolipolysis, BELIS provides the technical excellence your business deserves.
Ready to upgrade your practice with industry-leading technology?
Contact our experts today to find the perfect system for your salon
References
- Mohammad Radmanesh, Amir H. Naderi. Burning, paradoxical hypertrichosis, leukotrichia and folliculitis are four major complications of intense pulsed light hair removal therapy. DOI: 10.1080/09546630802132627
This article is also based on technical information from Belislaser Knowledge Base .
Related Products
- Clinic Use IPL and SHR Hair Removal Machine with Nd Yag Laser Tattoo Removal
- Diode Laser SHR Trilaser Hair Removal Machine for Clinic Use
- Diode Tri Laser Hair Removal Machine for Clinic Use
- IPL SHR+Radio frecuency machine
- Trilaser Diode Hair Removal Machine for Beauty Clinic Use
People Also Ask
- Why is SPF 50 mandatory after IPL for vascular lesions? Protect Your Skin and Ensure Flawless Results
- Can you use a hair removal device on private parts? A Safe Zone Guide for Intimate Areas
- How much do IPL treatments cost? A Guide to Investing in Clear, Smooth Skin
- Can I use my IPL machine every week? A Guide to the Optimal At-Home Treatment Schedule
- Does hair removal work better than shaving? Get Smoother, Longer-Lasting Results
