The ICH Guidelines is the common name applied to a widely-used lightfastness test for pharmaceutical and other home and personal care products. This test protocol is based on the International Conference on Harmonization’s publication Guidance for Industry: Q1B Photostability Testing of New Drug Substances and Products.
The ICH is a joint effort of U.S., European, and Japanese regulatory agencies. The intent of this standard lightfastness test is to verify that new products and drug substances do not exhibit “unacceptable change” when exposed to light. The diagram in Figure 1 shows that testing can be applied directly to the actual products or to inner or outer layers of packaging. The general idea is that if a product is affected by light, then it must be protected by either the immediate pack or the marketing pack.
Figure 1. ICH Guidelines test diagram proceeding top-to-bottom from testing substances directly, to immediate packaging, to marketing packaging. In each step an evaluation is made to whether “acceptable change” is observed. If yes, testing is stopped; if no, testing proceeds to the next layer.
The ICH Guidelines test is unique in specifying test duration in terms of both a minimum irradiance of total ultraviolet (TUV) wavelengths (300-400 nm), as well as a minimum total illuminance of visible light (400-800 nm) over the duration of the test.
Irradiance and Illuminance Explained
The ICH Guidelines procedure requires that test specimens be exposed to both a minimum UV irradiance and a minimum illuminance. While irradiance simply measures the total energy over time from the light source’s photons, illuminance takes that energy and applies the human photopic response curve.
The irradiance calculation is straightforward:
• Start with the irradiance (W/m2/nm) at each wavelength, referred as the Spectral Power Distribution (SPD), for the optical filter in use.
• Sum the irradiance values at each wavelength from 300-400 nm (Total UltraViolet or “TUV”)
• Multiply this number by exposure time, measured in hours, for total irradiance energy (expressed in W·h/m2)
• Example: 40 W/m2 × 10 h = 400 W·h/m2
The illuminance calculation is a bit more involved, as it involves multiplying the filtered light source SPD by the “photopic response” curve, which is a measure of how the human eye perceives light.
Again start with the SPD for the optical filter in use.
• Multiply each individual irradiance value by that wavelength’s photopic response value (lumens/W) to get a value in lumens/m2 (units of illuminance per area, also known as “Lux”)
• Sum those calculated illuminance values over all wavelengths. Only visible wavelengths will have non- zero values.
• A single wavelength illuminance calculation is given below:
Wavelength (nm) Photopic Response (lumens/W) Irradiance (W/m2) Illuminance (lumens/m2 or LUX)
555 683.00 x 0.33 = 227.2
This calculation is shown graphically in Fig. 2, where the xenon arc spectrum (red solid line) is multiplied by the human photopic response curve (green dashed line) to produce an illuminance curve (solid blue line). Total illuminance in Lux is represented by the area under the blue curve.
Figure 2
Irradiance and Illuminance in ICH Guidelines
The ICH Guidelines test requires the light stability test to be conducted until the point where both a minimum irradiance of 200 W·h/m2 and a minimum illuminance of 1.2 million Lux·h/m2 are reached. Two light source options for meeting these conditions are given in the text:
Option 1: A “D65/ID65 light source”, which is defined as an “artificial daylight fluorescent lamp combining visible and ultraviolet outputs, xenon, or metal halide lamp” and noting that “Wavelengths below 320 nm may be filtered.” This Option is met by Q-SUN testers.
Option 2: A cool white fluorescent and “near ultraviolet lamp.” This Option is met by QUV testers.
The two target minima given in the standard do not correspond specifically to either the D65 or ID65 reference light source. In fact, no single light source of any type can meet the visible light exposure conditions! In the case of the D65/ID65 type source, all lamps that fit that description will produce a significant over-exposure of the UV irradiance portion in order to meet the illuminance portion. In other words, an exposure long enough to deliver 1.2 million Lux·h/m2 to specimens will deliver more than three times the required 200 W·h/m2 of TUV irradiance.
Other Conditions in ICH Guidelines
Unlike the vast majority of weathering and lightfastness test standards, a test temperature (black panel or chamber air) is not specified in the ICH Guidelines test. However, Q-Lab’s view is that thermal degradation effects should be evaluated separately in heat aging tests, not during lightfastness testing. Therefore, testing at temperatures near normal room temperature (~25 °C air temperature) is recommended. This is achievable in QUV testers; in Q-SUN xenon arc testers, use of a chiller is required to maintain low temperatures. Higher irradiance setpoints in Q-SUN testers may make it more difficult to reach the low temperature setpoints, even with a chiller.
No requirements for moisture are given in the ICH Guidelines standard. Relative humidity is not specified and no water spray is introduced during the test.
Conclusion
The ICH Guidelines is a light stability test designed for pharmaceuticals and other home and personal care products. The QUV and Q-SUN accelerated weathering testers can both meet its dual requirements for irradiance and illuminance, provided that proper light spectra are known and test times are calculated. The Q-SUN test is performed in part with or without optional UV blocking filters, depending on the severity of the test required. The QUV test is performed via sequential exposures in a QUV/cw and an irradiance-controlled QUV/se or QUV/spray.
