ISO-CIE Damage Function (Tdw-ISO)

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Last Updated: August 1, 2024

The ISO-CIE damage function, also known as Tdw-ISO, is a method for calculating damage-weighted transmittance. This approach uses a weighting function recommended by the International Commission on Illumination (CIE) to assign specific damage weighted transmittance values to each wavelength of UV and visible light. The spectral range considered in this calculation spans from 300-700 nanometers (nm).

The purpose of Tdw-ISO is to provide a broader measurement of fading potential compared to traditional measurements like Ultraviolet Transmission (UVT). While UVT focuses solely on UV light’s contribution to material fading and degradation, Tdw-ISO considers portions of visible light along with UV that contribute to these effects.

The calculation for Tdw-ISO involves applying a damage-weighted transmittance value to each wavelength within its specified range. These values are assigned based on their contribution to material degradation and fading, as per the ISO-CIE function’s recommendations. The result is expressed in terms of transmitted daylight weighted by this damage function, providing an overall measure of the potential for fading, taking into account all the contributing wavelengths of light.

Comparison of Cardinal Fade-Control Products

Lower Tdw-ISO values indicate better overall fade protection for materials being tested. While no glass product can completely eliminate fading, a number of Cardinal glass technologies have been designed to slow the fading effect. The sample table below includes Cardinal IG using LoĒ™ coated glass, as well as combinations of LoĒ and laminated glass, which further reduces fade transmission.

LoĒ Product	Coating Type	Tdw-ISO (ISO-CIE)	UV Transmission
Quad LoĒ-452+	Clear	33%	1%
Quad LoĒ-452+ / 7.8L	Clear	31%	<1%
LoĒ³-366	Clear	43%	5%
LoĒ³-366 / 7.8L	Clear	39%	<1%
LoĒ³-340	Glare Control	27%	2%
LoĒ³-340 / 7.8L	Glare Control	25%	<1%
LoĒ²-240	Glare Control	35%	15%
LoĒ²-240 / 7.8L	Glare Control	28%	<1%

Notes: Entries above are in a 3mm dual pane IG unit. For IG with 7.8L, outboard lite is 3mm with inboard lite being laminated 3mm / .060 interlayer / 3mm.