Comparative evidence

dei̯h₂

• OInd. dī-, dīdī ‘shine’, ‘be bright’ (MW: 480; Whitney 1885: 74)

Whitney 1985: 74: “Compare √dīp-. Some confusion of forms is made between dīdī- and dīdhī-”.

References

MW = Monier-Williams, M. 1899. A Sanskrit-English Dictionary. Clarendon Press.
Whitney 1885 = Whitney W. D. 1885. The roots, verb forms and primary Derivatives of the Sanskrit language. A supplement to his Sanskrit grammar. Leipzig.