Simply put, lightfastness is the ability of pigment to resist fading when exposed to light, particularly sunlight.
Lack of lightfastness can cause your colors to go from this...
in a matter of just a few years.
How Do I Know If A Product Is Lightfast?
Some brands, like Liquitex make finding this out really easy by marking it right on the tubes. Otherwise, you can probably f8nd this information on the company's website.
Royal Talens, for example, offers a downloadable PDF with all kinds of info about their products, including their lightfastbess ratings.
How Long Does Paint Have To Last To Be Considered Lightfast?
From what I gather, anything that will last less than ten years, is considered to have poor lightfastness. Anything that will last at least a hundred years is excellent lightfast. Anything that will last twenty-five to fifty years has good lightfastness.
I've heard of colored pencils that will last 800 years and that to me sounds like phenomenal lightfastness.
How Important Is Lightfastness?
That depends on what you want to do with your piece. If you want to sell the original, lightfastness is very important. People who buy art invest a lot of money into it and they're not going to be happier with you if a piece they bought from you is faded and dull in a few years.
But if you're okay with not selling the original and maybe just selling prints, then lightfastness may not be that important.
I think it also depends on how long you're going to spend on the project. If I spent a long time on a piece, I would be more upset to see the colors fade quickly than if I didn't spend that long on it.
Painter of portraits and wildlife