Wikipedia
Bilawal is a raga and basic thaat ( musical mode) in Hindustani classical music. It is equivalent to the Carnatic melakarta raga Dheerasankarabharanam, as well as the Western Ionian mode (major scale) and contains the notes S R G m P D N S' (see swara for explanation). The pitches of Bilawal thaat are all shuddha, or natural. Flat (komal) or sharp (tivra) of pitches always occurs with reference to the interval pattern in Bilawal thaat.
It is one of the ragas that appears in the Sikh tradition from northern India, and is part of the Sikh holy scripture (Granth), the Sri Guru Granth Sahib. Every raga has a strict set of rules which govern the number of notes that can be used; which notes can be used; and their interplay that has to be adhered to for the composition of a tune.
In the Sri Guru Granth Sahib, there are a total of 31 raga compositions. Bilawal is the sixteenth raga to appear in the series. The composition in this raga appear on a total of 64 pages from page numbers 795 to 859.
Bilawal had become the basic scale for North Indian music by the early part of the 19th century. Its tonal relationships are comparable to the Western music C major scale. Bilawal appears in the Ragmala as a ragini of Bhairav, but today it is the head of the Bilawal thaat. The Ragmala gives Bilawal as a putra (son) of Bhairav, but no relation between these two ragas is made today. Bilawal is a morning raga to be sung with a feeling of deep devotion and repose, often performed during the hot months. Over 170 hymns were composed to this raga by Guru Nanak, Guru Amar Das, Guru Ram Das, Guru Arjan and Guru Tegh Bahadar.