Visible light communication (VLC) system is a promising wireless communication that does not interfere with radio waves. However, it performs different performances in daytime and nighttime due to light as its resource. This research investigates a VLC system using the NRZ-OOK technique by considering external light based on BER measurement. At 10 cm and 100 bps, the bright and low light BER values system are 0.3302 and 0.2504, respectively. Meanwhile, at data rates of 1 kbps and 100 kbps, the BER values are 0.2429 and 0.4387, respectively. This result can become a basis for performance optimization in the future.