Meaning
Measurement of light energy distribution across the electromagnetic spectrum provides the specific power levels at each individual wavelength. This spectral irradiance is typically measured in watts per square meter per nanometer to show where the energy of a light source is concentrated. Accurate data on this distribution allows for predicting how different lighting types will affect the color stability of printed materials.
A source with high energy in the uv range will cause faster fading than one concentrated in the infrared range.
Wavelength Distribution
Graphical representations of light output show the peaks and valleys of energy across the visible and invisible ranges. When analyzing spectral irradiance, technicians look for spikes in the blue and uv regions that are known to trigger the most severe chemical changes in inks. A mercury vapor lamp has a very different profile than a xenon arc lamp, even if they appear to have the same total brightness.
This difference explains why some packages fade in a laboratory test but remain stable in a retail store.
Laboratory Simulation
Testing protocols use this data to match the light output of an accelerated aging chamber to a real-world environment. By replicating the spectral irradiance of a specific retail bulb, a lab can provide a more accurate estimate of how long a package will last before the color shifts. This precision allows brands to select the most cost-effective inks and coatings for their specific distribution channel.
The simulation ensures that the test results are relevant to the commercial life of the product.
Material Response
Different pigments absorb energy at specific points along the spectrum. The spectral irradiance of the environment determines which pigments will remain stable.
