Tamas means darkness. The material world is dark, and beyond the material world is light. In other words, after passing through the entire material atmosphere, one can come to the luminous spiritual sky, whose impersonal effulgence is known as Siddhaloka. Mayavadi philosophers who aspire to merge with the body of the Supreme Personality of Godhead, as well as demoniac persons who are killed by Krsna, such as Kamsa and Sisupala, enter that Brahman effulgence. Yogis who attain oneness through meditation according to the Patanjali yoga system also reach Siddhaloka. This is a verse from the Brahmanda Purana.