Vaisesika Sūtra 5.2.19

द्रव्यगुणकर्मनिष्पत्तिवैधर्म्यादभावस्तमः ॥१९॥

dravyaguṇakarmaniṣpattivaidharmyād abhāvas tamaḥ ॥19॥

[द्रव्य-गुण-कर्म-निष्पत्ति-वैधर्म्यात् (dravya-guṇa-karma-niṣpatti-vaidharmyāt) - due to that which comes forth, contrary to dharma - in substance, quality, and movement; अभावः (abhāvaḥ) - lacuna; तमः (tamaḥ) - ignorance;]

The lacuna arising from that which comes forth, contrary to dharma, in substance, quality, and movement is 'tamas', i.e. darkness or ignorance.