Pharmaceutical Photostability Testing (ICH Q1B): Why Lighting Alone Is No Longer Enough

A pharmaceutical photostability test involves exposing a product to a controlled dose of visible and UV light, in accordance with the ICH Q1Bguideline, to verify that its quality, efficacy, and safety remain unchanged. Developing a pharmaceutical product is about more than just demonstrating its efficacy; it is also about proving that its quality, safety, and performance remain unaltered throughout its shelf life.

Among the many environmental factors that can affect a drug, light is one of the most critical. Uncontrolled exposure to visible light or ultraviolet radiation can have direct consequences:

• Degradation of the active pharmaceutical ingredient (API), as well as changes in appearance or color.
• Loss of the product's therapeutic efficacy.
• Formation of undesirable degradation products.
• Alteration of the stability of excipients and the formulation.

Photostability stability studies are therefore absolutely essential to prove that a pharmaceutical product maintains its quality after controlled exposure to light.

The true requirements of the ICH Q1B guideline

Globally, it is the ICH Q1B guideline that harmonizes photostability testing. The standard is clear and specifies that samples must receive at least:

• 1.2 million lux hours (lux.h) of visible light.
• 200 Wh/m² of ultraviolet radiation.

These exposure levels represent the minimum light dose required to properly evaluate how pharmaceutical products behave when exposed to light. The goal is not simply to illuminate samples for a given period. The real challenge is to demonstrate that the required light energy was actually delivered to the product under perfectly controlled conditions.

From theory to practice: the era of data integrity

For many years, photostability testing mainly consisted of installing compliant light sources and calculating the theoretical exposure time needed to reach the doses defined by ICH Q1B. While this approach remains widely used today, the expectations of the pharmaceutical industry have evolved significantly.

Today, Quality Assurance, Validation, and Regulatory Affairs departments expect far more than just theoretical compliance. During an audit or inspection, the question is no longer simply whether the product was exposed to light. Auditors now ask much more pointed questions:

• What dose of light did the samples actually receive?
• Was the exposure uniform inside the chamber, and how was this verified?
• Were the measuring instruments properly calibrated?
• Were the critical parameters recorded?
• Can the data be retrieved several years after the study?

In other words, the quality of the evidence has become almost as important as the study itself. Limited documentation can lead to additional questions during GMP inspections, requests for supporting evidence, or worse, delays in development programs or regulatory submissions.

The Caelis approach: traceability as a standard

Faced with these increased requirements, not all photostability chambers are created equal. While most equipment includes visible and UV light sources, their design philosophy differs significantly.

At CAELIS, a French company specializing in the design and manufacture ofclimatic chambers for the pharmaceutical industry, we have made a clear choice: one of robust scientific data, reproducibility, and exhaustive documentation.

Our goal is not just to design a climatic chamber capable of meeting ICH Q1B requirements. Our true mission is to provide laboratories with the tools necessary to concretely demonstrate how photostability studies were conducted.

The technology behind our Monoblock Phototest chambers

Our monoblock climatic chambers Phototest (available in 600 L, 1300 L, and 2000 L) integrate cutting-edge technology designed for compliance:

• 6500 K daylight LED panels.
• 385 nm UV-A LED panels compliant with the ICH Q1B Option 2 approach.
• Independent control of visible and UV lighting.
• Adjustable light intensity from 30% to 100%.
• Positioning measurement probes at the least favorable locations within the chamber to verify that each sample receives at least the minimum required dose.

This architecture ensures better exposure uniformity, increased study reproducibility, and easier integration into IQ/OQ/PQ qualification.

Take the next step with CAELIS

Today, in an increasingly regulated pharmaceutical environment, the value of a photostability climatic chamber is no longer defined solely by its climatic or lighting performance. Its true value lies in its ability to generate reliable, traceable, and scientifically defensible data throughout a product's lifecycle.

Choosing a CAELIS climatic chamber means ensuring that, months or years later, you can demonstrate that your studies were conducted under perfectly controlled and documented conditions.

Rest easy—your stability studies are in safe hands.

Ready to secure your photostability studies? Contact our experts →

Frequently Asked Questions — Pharmaceutical Photostability Testing

What light dose must a sample receive according to ICH Q1B? A minimum of 1.2 million lux-hours of visible light and 200 Wh/m² of UV radiation, delivered under controlled and verifiable conditions.

How can you verify that exposure is uniform within the chamber? By placing measurement probes at the least favorable locations in the chamber to ensure that every sample receives at least the required dose, regardless of its position.

What data must be kept after a photostability study? Critical parameters (dose received, instrument calibration, exposure uniformity) must be recorded and remain accessible for several years after the study to meet GMP inspection requirements.

What is the difference between Caelis Phototest chambers and standard equipment? Monoblock Phototest chambers combine daylight LED panels with 385 nm UV-A (ICH Q1B Option 2), independent control of both sources, and probe positioning at the least favorable points—providing data that is audit-ready, rather than just theoretical exposure.