why , when adding blue to the laundry, it makes it brighter . i mean to the white laundry?

Answer 1

It is illusionary. Blue tends to mask gray in the fabric, and give the appearance of being whiter.

Answer 2

Such Detergents have Optical brighteners

Optical brighteners are a broad classification of many different synthetic chemicals that, when applied to clothing, convert UV light wavelengths to visible light, thus making laundered clothes appear "whiter." Their inclusion in any formula does not enhance or affect the product's performance in any way; they simply trick the eye.


Some of Detergents that use optical brighteners are :

* 20 Mule Team Detergent (all versions)
* Ajax (all versions)
* All Liquid (all versions)
* All Free and Clear
* All Baby
* All with stain lifters
* Arm & Hammer FabriCare Powder (all versions)
* Arm & Hammer Fresh ‘n Soft Fabric Softener (all versions)
* Arm & Hammer Liquid (all versions)
* Arm & Hammer Perfume Free and Dye Free Liquid Detergent
* Arm & Hammer Super Washing Soda
* Asta
* DeliCare Fine Fabric Wash (all versions)
* Dreft Liquid
* Dreft Powder
* Dynamo (all versions)
* Era Liquid (all versions)
* Fab (all versions)
* Gain Liquids (all versions)
* Gain Powders (all versions)
* Ivory Snow Liquid
* Ivory Snow Powder
* Persil
* Purex Powder (all versions)
* Purex Liquid (all versions)
* Purex Fabric Softener (all versions)
* Purex Baby (all versions)
* Rain Drops Water Softener and Detergent Booster
* SA8 Plus Concentrated Detergent
* SA8 with Bioquest Concentrated Detergent
* SA8 with Gelzyme Liquid Detergent
* SA8 Sensitive Laundry Detergent
* SA8 Tablets Laundry Detergent
* SA8 Concentrated Liquid Detergent with Fabric Softener
* SA8 Solutions Tri-Zyme Stain Pre-Soak and Detergent Booster
* SA8 Solutions Dry Chlorine Bleach
* Surf Liquid (all versions)
* Suavitel Fabric Softener (all versions)
* Tide Liquids (all versions)
* Tide Powders (all versions)
* Tide Tablets (all versions)
* Wisk (all versions)
* XTRA Laundry Detergent
* Yes (all versions)
* Zout (all versions)
* All laundry products made by Colgate-Palmolive

Answer 3

UV --> Light, Blue and UV are very related.