With the deal, Mitsui Chemicals is taking on French giant Essilor to grab market share in a sector growing twice as fast as that of traditional eyewear.
Until now SunSensors was a unit of the American glass manufacturer Corning.
Mitsui Chemical said it planned to act aggressively in this new market and sell light-sensitive lenses in competitive conditions.
It gave no details on how much it is paying for SunSensors.
The transaction comes in response to Essilor’s acquisition in April of the US firm Transitions Optical, world leader in so-called photochromic glasses for $1.8 billion.
It was the biggest transaction ever for the French group, world leader in lenses for glasses.
Mitsui Chemicals, which is active in a variety of speciality chemical sectors, posted sales of $15 billion in 2013.