What is Lightfastness?

written by Melissa Wolck

You may have heard the terms “lightfastness” or “colorfastness to light” when shopping for the perfect outdoor fabric. Maybe you have seen a lightfastness rating or a particular number of light hours listed on a fabric's specs, but maybe you didnt know what they meant or fully understood their significance. Let’s discuss!

Lightfastness or Colorfastness to light is, “the degree to which a dye resists fading due to constant light exposure.” Although this may be particularly important when shopping for fabric that will be used in a sunroom or outdoors, it is important to note that all dyes have some susceptibility to light damage. Problems with fading tend to occur when the fabric chosen was not produced to meet the end use, like using a basic multipurpose cotton print on patio furniture.


Most fabric manufacturers complete UV tests that provide consumers with a rating that directly correlates with the fabric’s ability to resist fading or it’s lightfastness. The most commonly used method in the United States is the American Standard AATCC 169.3. With this test the fabric is exposed under specific conditions to a controlled light source which simulates the sun spectrum of Albuquerque, New Mexico. At timed intervals, the test swatch is compared visually to a gray scale and the degree of fading is rated on a scale from 1 to 5.

1 = Very Poor, High Degree of Fading

5 = Very Good, No Fading

AATCC 169.3 American Standard Test

Manufacturers may also provide a lightfastness in number of sunlight hours. Any number of hours could be given, but outdoor fabrics usually rate anywhere from 500-2000+. The exact number of hours or years a fabric will last without fading is impossible to determine as there are many factors that come into play, such as the type of dye used, fiber content of the fabric, sun intensity and geographical location.

Let’s take a moment to consider the difference of the sun’s intensity in New York compared to that of New Mexico.

Other factors that may affect lightfastness include temperature, humidity, and airflow.

Global Solar Intensity Potential

Keep in mind that we are affected by the sun’s UV rays all year round and even on overcast days. The sunlight that shines into our rooms in both summer and winter can cause color fading. Line draperies with protective lining, consider the harshness of the sun’s light through your windows, the number of hours of direct sunlight, and whether or not your fabric will be protected by the shade when selecting your fabric.

Check with your Greenhouse Fabrics customer & fabric specialist to find out the lightfastness rating of a particular fabric. We are happy to help you make the best selection for your space, but remember that ALL fabrics will fade over time.