How to Determine Polycarbonate Yellowing Index

Do you know how to Calculate the polycarbonate yellowing index? In this article, you will know it. Also get to know the process of determining delta YI.

Yellowing Index

The yellow index (YI) is a spectrometric data which is used to describe any change in colour of a test sample clear (white) toward yellow.

This may be due to a natural or an artificial source of light.

In industries, it is measured in terms of “delta YI”which is denoted as ΔYI.This test is mainly based on determining the difference in colour of a product at any given point in the products life cycle and the original product.

For instance, when a polycarbonate sheet is exposed to the ultraviolet radiation, it will turn yellow after sometime.This change in colour is referred to as the polycarbonate yellowing index.

Ideally, the YI testing involves a series of comparative measurement and analysis for a given period of time.

It is important to handle the test sample carefully since some surfaces can easily be modified.This will definitely result into erroneous conclusions.


The yellow index is one concept which is fundamental in most industrial processes.

This is for the reason that they use this test to process substances which are likely to result into yellowing. It is used to gauge the purity of a substance etc.

These are some of the main reasons why polycarbonate yellowing index is used to determine the extent to which a polycarbonate product has degraded when exposed to either artificial or natural source of light which emits ultraviolet radiation.


The polycarbonate yellowing index is a crucial concept since it forms the foundation from which the polycarbonate sheet manufacturers and suppliers calculate their warranty period.

Incorporating the UV protective layer prolongs the lifespan of these sheets since they are very vulnerable to this radiation.For instance, for a high performance UV-protection layer, it may take quite a long period of time before the polycarbonate sheet begins to degrade.


Apparently, there are two main types of yellowness indices which are used in industrial setup and they include:

  1. The AST Designation D1925-70 which is as Standard Test Method for Yellowness Index of Plastics.
  2. ASTM Designation E313-73 which was reapproved in 1993 and it is the Standard Test Method for Indexes of Whiteness and Yellowness.

There is certain criteria that every product whose YI is being tested should meet.

That is, for the case of E313 test, the sample’s colour should be almost white or opaque and the items which are being compared should be have a similar transparency, texture and gloss among other physical properties.

These tests are very accurate and one may not be able to perform them at home since they’re costly.

Basically,the polycarbonate yellowing index can be calculated using the following equations:

This is for the case of the E313-73 yellowness index calculation.On the other hand,to calculate the yellowness index using the D1925 method then the following formula can be used:

Where for the two scenarios,the values of x, y and z are referred to as the tristimulus values.that is,the amount of the three primary colors in the visible spectrum (380-780 nm).

It can be a tedious process and thus,most manufacturers will conduct all the experiments and indicate all the necessary details about the polycarbonate yellowing index in their data sheets.

so now you know YI, it is very important factor to determine the quality of your polycarbonate sheet.

And of course if you want to know more about yellow index, you need to learn more about UV, UV is the key factor when you find your panels become yellow.

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