The American standard USP 1072 aims to ensure that all surfaces in controlled environments (clean rooms, isolators, sterile production areas) are treated in such a way as to limit bio-load and the risk of cross-contamination. The disinfection process must comply with the classification level of the rooms (ISO-5 to ISO-8), be compatible with the materials, respect the integrity of personnel, and leave no chemical residue after treatment.

The disinfection of production premises using Intense Pulsed Light falls within this scope. As with any other process, efficacy tests must be carried out at various critical points. The robustness of the protocol must be demonstrated. The SAL (Sterility Assurance Level) will be defined by the production entity manager in conjunction with microbiological monitoring and will enable the protocol to be adapted to the desired objective.

In addition, Intense Pulsed Light currently achieves a logarithmic reduction of 10-6 on Geobacillus stearothermophilus.

This disinfection potential means that it meets the requirements of USP 1229 for the sterilization of pharmaceutical and medical devices (in situ tests carried out at 100mJ/cm2 on strain ATCC 7953 by Biopulz, 2023).

Like VHP technologies, this technology could fall under subsections 1229.11, which defines the process (VHP/steam), and 1229.14, which requires validation, i.e., demonstrating, in the industrial configuration (materials, load, geometry, bioburden, type of items, exposure, etc.), that the process reliably reduces the population of microorganisms, preserves the integrity of materials, and is reproducible with a SAL target of 10^-6.

Today, this new use is not listed by the USP due to the novelty of this technology, which will undoubtedly need to be documented in order to be included in USP practices.

1. History of the development of intense pulsed light

Intense Pulsed Light (IPL) uses very short flashes of light (a few microseconds) emitted by a xenon lamp. As a reminder, the light spectrum emitted covers ultraviolet A, B, and C, visible light, and infrared. The entire light spectrum can be used to destroy the DNA of microorganisms through photodestruction.

In the 1980s and 1990s, intense pulsed light was developed for medical and cosmetic applications (hair removal, dermatology). At the same time, researchers explored its germicidal potential, particularly against bacteria, yeasts, and spores.

In the early 2000s, the first scientific studies demonstrated the effectiveness of IPL for disinfecting surfaces and packaging in the food industry. At the same time, this technology began to be adapted to meet the strict sterilization standards of the pharmaceutical industry.

In the mid-2000s to 2010, this technology was gradually deployed in the pharmaceutical industry to sterilize sensitive components in clean room environments (blister packs, vials, plastic films). This new technology is recognized for its various advantages: speed of treatment and no use of chemicals. As it does not produce heat, it is compatible with heat-sensitive materials.

Since the 2010s, this technology has been tested in experimental protocols for the disinfection of various types of packaging, including Tyvec packaging. The companies in charge of these developments are now aiming to validate compliance with USP 1229 and 661 standards. This would allow them to integrate this technology into automated production lines to ensure continuous aseptic disinfection.

Current research focuses on optimizing parameters (duration, intensity, distance, flash repetition). The use of LIP is growing in the disinfection of air and surfaces in critical areas in the pharmaceutical industry. Researchers are attempting to test the effectiveness of LIP against resistant pathogens and bacterial spores.

2. Specific features of different light technologies

2.1 Ultraviolet-C

Ultraviolet-C is a simple, proven technology that is effective at short distances (3-4 cm), ideal for continuous surface or air disinfection. However, it is not very effective on spores or resistant bacteria.

UV-C radiation is produced by mercury lamps or LED lamps. It works by degrading the DNA, RNA, and proteins of microbes, which inactivates them by blocking their replication. Current applications of this well-documented technology include surface, air, and water disinfection. UV-C poses a risk to human health (skin, eyes) because this process is often used in close proximity to personnel.

2.2 Laser

Laser technology is very precise and powerful. It involves a monochromatic, directional light beam that targets very limited areas.

Its mechanism of action depends on the type of laser and the wavelength. UV lasers (Excimer 248–308 nm, 222 nm KrCl) have a similar action to conventional UV-C.

Visible and infrared lasers enable disinfection through thermal effects (heating, carbonization, perforation of bacterial membranes). The main applications are targeted treatments for medical devices used in sterile surgery (pipettes, surgical instruments). It is not suitable for disinfecting large surfaces. This technology presents risks of burns to personnel and thermal damage to equipment.

2.3 Intense pulsed light

Intense pulsed light (IPL) combines high power, a broad light spectrum, and the ability to treat large surfaces.

It is effective against a wide variety of microorganisms, including bacterial spores (EN 17272- BIOPULZ 2021 standard), and is particularly suitable for the pharmaceutical industry for rapid disinfection operations without chemical residues. Its action is based on the emission of very high-intensity flashes (irradiance in mW/cm²) covering a broad spectrum from 200 to 1100 nm, encompassing UV, visible, and infrared light.

This combination enables microbial inactivation through photochemical (DNA alteration, free radical production), photothermal (rapid and local temperature rise), and photophysical (mechanical effects related to the light wave) mechanisms.

PLS is therefore a non-thermal method of rapid decontamination, suitable for heat-sensitive surfaces.

Its effectiveness varies depending on several parameters: the number of flashes, the distance between the source and the treated area, and the nature of the targeted microorganism. The loss of energy due to the distance between the surface to be disinfected and the light source will be compensated by increasing the number of flashes.

The total amount of energy delivered by all flashes during a single treatment cycle is measured by a physical parameter: fluence, expressed in mJ/cm² (see definition below). Fluence is one of the key values of this technology.

3. Fluence and irradiance

As previously mentioned, fluence and irradiance are two essential physical parameters for understanding the LIP disinfection process.

3.1 Fluence

Fluence (F) corresponds to the light energy received per unit area, expressed in mJ/cm².

According to the literature, the effectiveness of disinfection is directly correlated with fluence: each microorganism has a threshold dose, or critical fluence, above which its inactivation is guaranteed. The relationship is dose-response: the higher the fluence, the greater the logarithmic reduction. (A. Wekhof, 2000)

As a guide, a fluence of 0.5 to 1 J/cm² achieves a 2 to 3 log reduction for E. coli, while fluences of 5 to 10 J/cm² achieve reductions of 5 to 6 log.

At low fluence, the predominant effect is photolytic, mainly related to the action of UV-C on DNA, while at high fluence, thermal and mechanical effects are added, considerably amplifying the inactivation efficiency. However, bacterial spores and molds require significantly higher fluences, often exceeding 80 mJ/cm², unlike viruses, which are more sensitive.

In practice, the choice of fluence required to achieve a given reduction level (e.g., 5 log) must be based on bibliographic data and calculations to determine the number of flashes required. These calculations take into account the distance to the object on the surface to be disinfected. The qualified protocol must also take into account the nature of the materials exposed and their sensitivity to pulsed light, in accordance with USP-1072 recommendations. Accurate mapping of the areas to be treated is essential beforehand in order to take into account critical areas that could compromise the effectiveness of the treatment.

The sensitivity of materials to this technology is a key issue.

Similarly, the introduction of disinfection or sterilization processes using VHP or peracetic acid or hydrogen peroxide misting has already led manufacturers to adapt their production rooms to prevent oxidation caused by these methods on equipment and materials.

Tests carried out by the Praxens laboratory for BIOPULZ show, for example, that the material “Mipolan” begins to discolor after 30 series of 23 flashes at 1 J/cm², i.e., a cumulative dose of 690 J/cm².

Effective treatment against bacterial spores requires only 100 mJ/cm²: the material would therefore only show signs of deterioration after 69,000 disinfection cycles, which represents nearly 5,750 months at a frequency of one cycle per month. Other materials will need to be tested to document this essential aspect.

3.2 Irradiance

Irradiance (denoted by E, in watts/m²) is the optical power received per unit area perpendicular to the light beam. It characterizes the instantaneous optical power received at a given moment on a surface.

Light fluence (denoted by H, in Joules/m²) is the total amount of light energy received per unit area during a given time interval. It therefore corresponds to the time integral of irradiance.

This relationship is fundamental for evaluating the effect of light exposure (such as intense pulsed light) on a target surface, particularly for disinfection or photochemical treatment applications. Irradiance describes the instantaneous intensity, while fluence reflects the total dose of energy received, a critical parameter for the inactivation of microorganisms. As we see in these various studies, the result obtained in terms of logarithmic reduction is correlated with the fluence value, which is itself correlated with the irradiance value.

3.3 How is fluence measured?

Two approaches are commonly used to measure fluence.

The first is based on colorimetric indicators, which evaluate fluence at a specific wavelength. Like any colorimetric device, they involve some interpretation and provide only an approximate estimate. However, their low cost and ease of use make them useful tools when introducing pulsed light into a new environment.

The second approach uses electronic fluence sensors. However, the models currently available on the market cannot measure high fluences because the photoelectric cells they incorporate are quickly saturated by the levels generated by intense pulsed light. To date, fluence can therefore only be measured at a given wavelength, mainly in UV-C.

Nevertheless, a new generation of sensors, specially designed for intense pulsed light and benefiting from appropriate calibration, is beginning to emerge. Fluence remains the central element in the disinfection process: it can be likened to the amount of active ingredient in a biocide, its effectiveness increasing in proportion to the dose received.

4. Main light-based disinfection processes used in industry

(See Tab1) In devices using IPL, the lifespan of the xenon lamps used in IPL is estimated at 1 million flashes.

To ensure the reliability of the lamp, two sensors have been developed: an irradiance sensor and a fluence sensor.

The irradiance sensor, located at the light source, measures the flash emission power, ensuring that there is no deviation from the irradiance defined during performance qualification (PQ).

The fluence sensor is mobile and measures the amount of energy/cm² received by the treated surface. This sensor is subject to annual metrology by a certified body (National Testing Laboratory).

These two sensors ensure that the lamp is functional in relation to the values defined during performance qualification (PQ). When the sensor values are incorrect, the disinfection cycle is invalidated, which means that the xenon lamp must be replaced, regardless of the number of flashes it has produced.

The theoretical lamp life is therefore reassessed at each disinfection cycle to ensure that the parameters defined during the PQ are maintained.

5. Understanding the disinfecting effectiveness of intense pulsed light by reviewing the scientific literature

How does intense pulsed light enable rapid, effective, and residue-free disinfection?

What about the results observed and how do they correlate with the intensity of the flashes emitted? One of the most comprehensive studies, published in June 2000 in the PDA Journal of Pharmaceutical Science & Technology, shows a correlation between disinfecting effectiveness expressed as logarithmic reduction and fluence (J/cm²).

We also offer a review of the various studies conducted on different media.

As can be seen below with biocides, not all microorganisms have the same sensitivity to LIP. (See Tab2 & Tab3)

6. What types of bioindicators should be used to measure the performance of IPL?

Bioindicators are used to reproduce contamination and its disinfection process in a given environment.

In the case of pulsed light, as with other light-based technologies, bioindicators specifically developed for this method are rare on the market, if not non-existent.

To ensure that the operation is adequately represented, three conditions must be met.

First, it is necessary to use a microorganism recognized in the pharmaceutical industry: Geobacillus stearothermophilus (ATCC 7953) is the reference strain recommended by pharmacopoeias (USP, Ph. Eur., JP) and ICH guidelines, particularly for the validation of sterilization cycles in accordance with ICH Q8, Q9, Q10, and the EMA and FDA guidelines.

Next, it is important to select a bioindicator (medium and protocol for distributing strains on the medium) specifically designed for intense pulsed light and not a device intended for other technologies, such as hydrogen peroxide or VHP.

Finally, the germs must be kept in a single layer in sterile water before being dispersed on the medium in order to avoid the formation of agglomerates that could bias the evaluation. (see Tab4)

7. Emerging applications of intense pulsed light in industry

Intense pulsed light (IPL) has strong potential for development in the pharmaceutical industry, as it enables rapid disinfection or SAL-6 disinfection without heat or the use of chemicals.

It has a variety of applications, including the disinfection of pharmaceutical packaging such as glass or plastic vials, ampoules, pre-filled syringes, as well as blister packs, plastic films, seals, and caps. LIP thus makes it possible to effectively treat the surface of containers before aseptic filling, while avoiding the use of agents such as ethylene oxide or hydrogen peroxide.

This technology is also suitable for disinfecting sensitive instruments or medical devices, such as pipettes, microneedles, catheters, or endoscopic probes, especially when the materials cannot tolerate heat or moisture. It is therefore an attractive alternative to conventional processes such as autoclaving, ethylene oxide, or hydrogen peroxide plasma.

In pharmaceutical production, LIP can also be used to decontaminate critical surfaces, conveyors, contact areas, bottle necks, and for rapid treatment of air or large surfaces in clean rooms.

In research and development, IPL can be used to inactivate viruses and bacteria to obtain non-infectious samples, for example in the context of work on vaccine candidates, or to deactivate biological contaminants in pharmaceutical raw materials.

Compared to traditional processes, intense pulsed light stands out for its speed (a few seconds are enough), the absence of solvents or residual chemicals, its compatibility with heat-sensitive materials, and its broad-spectrum action covering bacteria, spores, viruses, yeasts, and molds.

However, certain precautions are still necessary, particularly due to the risk of photochemical degradation of sensitive active ingredients, which requires a prior compatibility study.

In the context of disinfecting production environments, intense pulsed light offers significant advantages with regard to current regulatory requirements, particularly those of Annex 1 of the ICH guidelines, which require the total absence of residues after bio-cleaning and disinfection operations.

At the same time, the need to protect operators from the harmful effects of certain chemical agents and to limit the environmental impact of processes is encouraging manufacturers to adopt technologies that are effective, residue-free, and pose no risk to human health.

In this context, intense pulsed light is a particularly suitable solution, which explains its growing use for the disinfection of RABS, isolators, material airlocks, personnel airlocks, and production rooms.

Conclusion

Intense pulsed light, an athermic process, is establishing itself as an innovative, effective, chemical-free, and environmentally friendly disinfection technology. Initially developed for medicine and cosmetics, its germicidal potential has been progressively evaluated and validated in the food and pharmaceutical industries.

Unlike other light technologies such as UV-C or laser, intense pulsed light combines a broad light spectrum with high power, enabling it to be effective at long distances (several meters) and offering rapid inactivation of many microorganisms, including bacterial spores. Its effectiveness is based on photochemical, photothermal, and photophysical mechanisms, which are strongly correlated with light fluence, a key parameter in the effectiveness of the treatment. New, specifically adapted sensors are being developed because measuring this fluence remains complex.

The validation of intense pulsed light also requires the use of specific bioindicators. Geobacillus stearothermophilus, a standard strain in the pharmaceutical industry, is used as a reference but requires special preparation.

Faced with regulatory requirements such as the absence of chemical residues, intense pulsed light meets the growing need for clean, rapid disinfection that is compatible with sensitive materials. Today, its applications are expanding to new equipment (RABS, isolators, airlocks, etc.) with a view to controlling microbiological risk.

This new technology is set to become a future pillar of eco-responsible aseptic processes.