In the next 20 years, energy consumption is expected to increase up to 30% and it will affect energy crisis. Energy crisis can be resolved by energy efficiency. The context of this paper is about the energy efficiency of a mobile robot in the industrial warehouse. Communications media which commonly used in mobile robot navigation such as Laser need large power consumption. In order to reduce power consumption, the system of this paper is designed to use visible light communication (VLC) for mobile robot navigation because VLC only utilize lights as the transmitter. Method of this paper is sending the data contained navigation coordinates which modulated on the lighting system, then data will be received by the photodetector and processed as mobile robot's navigation. From above system, by using 5,68-watt power on lighting system can be used to transmit navigation data with the range up to 2 meters. In the receiver side, a photodetector which uses as receiver generate maximum power 4,14 watt at 10 cm of height between transmitter and receiver while minimum generated power is 3,21 watt at 250 cm of height. The conclusion of this paper is generated power by a photodetector in navigation process mobile robot is affected by angle and distance between transmitter and receiver.

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Underwater wireless optical communication (UWOC) has been considered a promising technology for high-speed underwater transmission. Some Gb/s level UWOC systems applying visible light have been demonstrated with a transmission distance of several meters or more. Many of the previous works focus on the advanced technologies to push the systems’ capacity–distance performance. However, practical environmental factors issue such as flow turbulence and temperature variation are seldom studied through specific statistical/theoretical models. In this paper, a UWOC system using a 450 nm blue light laser source was set up using a 1.5-m water tank with mirrors located on both sides for single or multiple reflections corresponding to different transmission distances. The blue laser was modulated by a 1.25 Gbps NRZ-OOK format with PRBS of 7, 24 or 31, respectively, for system performance comparison. The bit error rate (BER) values were measured in 1.5, 3.0 and 6 m, respectively, for system evaluation. At room temperature, the BER value was down to 10 × 10−8 for a 1.25 Gbps data rate in a 6 m transmission. Then, the UWOC transmission system experiment was carried out under several environmental parameters such as temperature, turbulence, artificial seawater by adding salt to simulate practical application in river or sea. When a submerged motor with an output of 1200 L/h was used as a water flow turbulence source, the impact to BER and transmission quality was negligible. For the temperature change issue, the experiment shows that around the original temperature of 25 °C had the best BER as compared to other temperature ranges from 10 to 50 °C. For artificial seawater issues by adding salt to simulate the real seawater environment. The transmission distance was only 3-m instead of 6 m, mainly due to particle scattering and water disturbance. With the motor pump on, the power penalty was 1 dB at 10 × 10−8 BER when compared to the motor pump off.

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