1. The lit field - That portion of the space which is pervaded by the heat of the sun. There are two suns in the Jambūdvīpa; when the day is of 18 Muhūrttas (1 Muhūrtta=48 minutes) each sun lights 3/10 part of the Jambūdvīpa. The circumferences of the Jambūdvīpa is 316288 Yojanas (1 Yojana=7.88 kilometers). 3/10 part of that circumference is - 31 6288x3/10= 948684/10 Yojanas. This is the lit field (of the Jambūdvīpa).
'sūriya'tti dvan sūryau jambūdvīpe......yadāpi dākṣiṇottarayoḥ sarvotkṛṣto divaso bhavati, tadāpi jambūdvīpasya daśabhāg.itrayapramānamcva tāpaksetram tayoh pratyekam syād.... utkrstadinam cāstādaśabhinnuhūrttairuktam......lavaṇasamudraṃ prati catnrnavatiryojanāṇāṃ sahasrāni astau śatānyastasastyadhikāni catvāraśca daśabhāgā yojanasyetyetadutkrstadine tāpaksetrapramānam bhavati.....jambūdvīpaparidheḥ kiñcinnyūnāṣṭavitnśatyuttaraśatadvayādhikasodaśasahastropetayojanalaksatrayamānasya dasabhirbhāge hrte yallabdham tasya triguṇitve etasya bhavāditi.
(Bhaga 5.3-7 Vṛ)
2. The length of the day - The time from sunrise up to sunset.
kṣetraṃ - sūryasambandhī tāpakṣetraṃ dinamityarthaḥ.
(Bhaga 7.24 Vṛ)