a glass composition including sio 2 in an amount from 30 . 0 to 40 . 0 % by weight , al 2 o 3 in an amount from 15 . 0 to 23 . 0 % by weight , b 2 o 3 in an amount from 0 . 0 to 15 . 0 % by weight , k 2 o in an amount from 0 . 0 to 5 . 0 % by weight , la 2 o 3 in an amount from 0 . 0 to 30 . 0 % by weight , li 2 o in an amount from 0 . 0 to 3 . 0 % by weight , na 2 o in an amount from 0 . 0 to 4 . 0 % by weight , nb 2 o 5 in an amount from 0 . 0 to 10 . 0 % by weight , tio 2 in an amount from 0 . 0 to 7 . 5 % by weight , wo 3 in an amount from 0 . 0 to 10 . 0 % by weight , y 2 o 3 in an amount from 15 . 0 to 35 . 0 % by weight , and ro in an amount from 0 . 0 to 7 . 5 % by weight is provided . glass fibers formed from the composition have a refractive index between 1 . 55 and 1 . 69 .