Allowed and forbidden transitions of singlet helium from 2s1Stons1S,np1P, andnd1Dstates have been measured betweenn=8 and 31 by optogalvanic spectroscopy in a dc discharge positive column. The addition of neon in the discharge was found to increase the relative intensities of the forbidden transitions. For similar photon flux, the optogalvanic signal reaches a maximum atn=11 and decreases thereafter. Neutral collisional ionization of the excited states fromn=13 and above was found to be responsible for the increased ionization efficiency of the high Rydberg states.