How does vowel length distinguish words in languages that contrast long and short vowels?

In languages that contrast vowel length, the duration of a vowel serves as a phonemic feature, meaning that changing the length of a vowel can alter the meaning of a word. This phenomenon, often referred to as quantity, allows speakers to distinguish between otherwise identical sequences of sounds.1

For example, in Estonian, vowel length is a critical component of its unique quantity system, which features three contrastive degrees of duration. This allows for distinctions such as vara (early) versus vaara (of the hillock) versus vaara (hillock), where the duration of the vowel a changes the word's meaning. Similarly, other languages may use a binary contrast between short and long vowels to differentiate lexical items.1

While tense vowels are sometimes associated with longer durations compared to lax vowels, this is a phonetic characteristic rather than the primary mechanism of phonemic length contrast. In systems where length is contrastive, the duration is typically a functional, independent feature of the language's phonology rather than just a byproduct of muscular effort.21