© 2017 IEEE. Light-fidelity (LiFi) extends visible light communication into high-speed and multiuser wireless networks. As in cellular networks, co-channel interference (CCI) stemming from other access points (APs) sharing the same transmission resources is the main limiting factor in the performances of the LiFi networks; therefore, it is important to study characteristics of CCI. This paper studies the statistical characteristics of aggregate signal interference iagg in downlink LiFi networks where LiFi-enabled APs are randomly deployed following a Poisson point process (PPP). One of the advantages of considering iagg compared to the aggregate power interference is that parameters of modulation schemes and room dimensions can both be incorporated. The paper's key finding is that the energy of $agg is not monotonically decreasing as the vertical distance of user of interest and the AP increases. In addition, we show that the distribution of iagg rapidly approaches a Gaussian distribution as PPP intensity increases.