What makes a fluorescent highlighter marker so bright?

What makes a fluorescent highlighter marker so bright?

Sharpie Accent Retractable Highlighters Fluorescent Yellow Pack Of 12 - Office Depot

BIC Brite Liner Highlighter, Assorted, 24 Pack - Chisel BICBL241AST, BIC BL241AST - Office Supply Hut

Sharpie Clear View Tank Highlighters Assorted 3ct

How do Black Lights Work, Why do Highlighters Look So Bright, and How Can You Impress Your Significant Other with Science? – Sustainable Nano

Avery® Hi-Liter Desk-Style Highlighters - Chisel Marker Point Style - Light Blue, Light Green, Light Pink, Yellow Water Based Ink - Yellow, Light Green, Light Blue, Light Pink Barrel - 4 / Box

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Integra Pen Style Fluorescent Highlighters Chisel Marker Point Style Fluorescent Pink 12 Dozen - Office Depot

VTOM 4pcs Soft Tip Highlighter Pen Set Pastel Light Color Fluorescent Marker Pen Kawaii Stationery Set For Kid Student