In general, tense vowels are more close (and correspondingly have lower first formants) than their lax counterparts.
Korean, for example, has a three-way contrast among stops and affricates; the three series are often transcribed as [p t tɕ k] - [pʰ tʰ tɕʰ kʰ] - [p͈ t͈ t͈ɕ k͈].
In this case the definition of "tense" would have to include greater glottal tension; see Korean phonology.
In some dialects of Irish and Scottish Gaelic, there is a contrast between [l, lʲ, n, nʲ] and [ɫˑ, ʎˑ, nˠˑ, ɲˑ].
Tenseness is especially used to explain stop consonants of the Alemannic German dialects because they have two series of them that are identically voiceless and unaspirated.