Bleach can brighten up old and faded shirts. It’s found in most detergents, and you can even use concentrated bleach to make your clothes appear even whiter. But here’s the surprising part: bleach doesn’t actually clean your clothes – it manipulates light to make them look whiter and brighter.
Manipulate light? Yes! Bleach (specifically optical brighteners in it) absorbs ultraviolet (UV) light found naturally in sunlight and some indoor lighting, and then re-emits it as blue visible light.
This blue light counteracts yellow tones in clothing, making our eyes perceive the fabric as cleaner and brighter.
So: when a white garment starts to yellow from sun exposure or repeated washing, the extra blue light helps mask the yellowing – making the clothes look whiter and fresher, even though no actual dirt has been removed.
Now that summer is approaching and white t-shirts and shirts are coming out again, here’s a trick:
If you wash your clothes with bleach, wear them after sunset for the best effect – the blue light reflected from your garments will stand out more and make your shirt shine. During the day, however, the air is already filled with visible light, which can reduce the reflective effect.