13.18 This (self) alone is the 'light' which illuminates things like the sun, a lamp, a gem etc. It is knowledge alone in the form of the effulgence of the self which illuminates a lamp, the sun etc. But a lamp etc., dispel the darkness that intervenes between the sense of sight and its subject. Their illuminating power is limited to this extent. This is said to be beyond Tamas (darkness). The term Tamas denotes Prakrti in its subtle state. The meaning is that the self transcends Prakrti. Therefore, It is to be comprehended as knowledge, i.e., to be understood as of the form of knowledge. It is attainable by means of knowledge - such as modesty etc., already described. It is present in the heart of all, i.e., It is specially settled, or present in the heart of all beings like men etc.