Optical wireless communication (OWC) system uses intensity modulation with direct detection (IMDD) to modulate the intensity of the signal in order to transmit information. There is an increase in the exploration of the modulation techniques used in visible light communications (VLC) in recent times. This paper deals with the comparison of power efficient modulation techniques such as dual-header pulse interval modulation (DH-PIM) and digital pulse interval modulation (DPIM) for VLC systems. Further, power allocation is studied under AWGN and Rayleigh channel. It is seen that the results prove to be spectrally efficient in the analysis of MIMO-OFDM VLC systems.