Is this common knowledge or is it just me who didn't know of this?
How did I not know this?
Despite what the adverts say, it is very difficult to transform grubby clothes into dazzling whites with nothing but elbow grease. To get around this problem, washing powder manufacturers add a special substance (called an optical brightener) that absorbs UV light.
...
Converting the invisible UV into blue light makes the clothes look brighter and gives the impression of being whiter than white.
Despite what the adverts say, it is very difficult to transform grubby clothes into dazzling whites with nothing but elbow grease. To get around this problem, washing powder manufacturers add a special substance (called an optical brightener) that absorbs UV light.
...
Converting the invisible UV into blue light makes the clothes look brighter and gives the impression of being whiter than white.