Raga Bilawal or Bilaval
Raga Bilawal is the most basic raga in Bilawal thaat. Indeed, the name of the thaat is derived from this raga. Interestingly enough, this raga has been declining in popularity over the years. Bilaval or Bilawal is a raga and the basis for the eponymous thaat (musical mode) in Hindustani classical music. Raga Bilaval is named after Veraval, Gujarat. This raga is sometimes referred to as Shuddha Bilawal to distinguish it from the more popular Alhiya Bilawal.
Bilaval 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. Bilaval appears in the Ragamala as a ragini of Bhairav, but today it is the head of the Bilaval thaat. The Ragamala names Bilaval as a Putra (son) of Bhairav, but no relation between these two ragas are made today. Bilaval is a morning raga to be sung with a feeling of deep devotion and repose, often performed during the hot months.
Bilaval is one of the ragas that is in the Sikh tradition from northern India, and is part of the Sikh holy scripture (Granth), the Sri Guru Granth Sahib.
Bilawal is considerd by most to be Sampurna - Sampurna. However, some are of the opinion that it should be considered Shadav - Sampurna due to the weakness of its Ga in the arohana.
The vadi / samavadi theory is generally discounted by modern musicologists, but for those who are inclined to follow this, it has been suggested that the vadi and samavadi are Dha and Re respectively.
Raag Bilawal exudes a bright and positive mood. It is traditionally performed during the morning hours, from 6:00 a.m. to 9:00 a.m.
At the initial stage, gurus in the Hindustani music tradition often choose to teach ragas Yaman and/or Bhairav. But rudimentary exercises are often taught using shuddha swaras or notes that do not use their komal or flat and teevra or sharp varieties. Such a scale is called Bilawal and is treated as one of the 10 parent scales according to the system of raag classification evolved by musicologist and music educationist Vishnu Narayan Bhatkhande (1860-1936).
Bilawal is also treated as a raga and lends its ragang or characteristic melodic features to several different ragas. Some musicians also call this raga Alhaiya Bilawal, but others differentiate between the two because the latter uses the komal variety of the Nishad or the seventh swar.
Credits:
https://chandrakantha.com/ and https://en.wikipedia.org/
https://learnharmonium.com/
https://scroll.in/article