R' constant in Balmer's formula is connected with< Rydberg's constant R, or ionisation energy of hydrogen atom with a dependence:
R’=R/hc, where c is a lighr speed and h Planck's constant.
Rydberg's
constant in energetic units [eV] is R=13,6 eV
and in "spectroscopic" units is: 6,7,8,9,10, pardòn 109 678 cm-1.