## 4 Experimental Details and Results for VLC Using Designed Lamp  
The DL was simultaneously used for illumination and data transmitter through a digital switching network. From Figure 8a, LED was modulated with a MOSFET (IRF 540) for sending a 2-kbps pseudo-random bit sequence (PRBS) signal, 5 V (pp) with an offset of 2.5 V, length \(2^{11}-1\) (11 is the length of shift register), and rise time of 12 ns, generated by a function generator (Rigol DG952, 250 MSa/s). The PRBS signal is a non-return-to-zero (NRZ), an on-off-keying signal used to modulate the light. It is a bitstream mapped onto a time scale that serves as input to the base of MOSFET. At the collector terminal of MOSFET, the constant current power supply is connected to (Lisun, DC3005S) for biasing. A source terminal of MOSFET is kept at ground potential. Power supply stability is tested by gated-FFT of its voltage level, which shows a 48 MHz ripple frequency that cannot interfere with the transmitted signal. The FFT of background intensity on the photodiode exhibited a peak at 104 Hz with a power level of \(-28\) dBm and another at 50 Hz with a power level of \(-36\) dBm. The Telefunken S-153 P photodiode collects light from ambient air. It has a radiant sensitive area of 7.5 mm\({}^{2}\), diode capacitance of 75 pF, half angle sensitivity of 55\({}^{\circ}\), rise time of 100 ns, spectral bandwidth of 600-1050 nm, responsivity of 0.6 A/W, and noise equivalent power of \(1.4\times 10^{-14}\) W/\(\surd\)Hz. A trans-impedance amplifier converts photocurrent to electrical voltage and is displayed on a real-time oscilloscope. Figure 7: Electroluminescence (EL) spectra of (**a**) WL and (**b**) DL for varying current from 10 to 55 mA input current. DL requires less input power consumption than WL to generate a photocurrent of 5 \(\upmu\)A at the photodiode. In Figure 8a, the left side shows the schematic arrangement of multi-color LED(s) with reflector cup and acrylic diffuser. LEDs were fixed on an aluminum metal-based heat sink. According to the datasheet [56], five-watt LEDs require a heat sink with a minimum surface area of 10,300 mm\({}^{2}\). From this data, we estimated that one three-watt LED would require a heat sink of size 6180 mm\({}^{2}\) and seven such LEDs would require a minimum surface area of 43,260 mm\({}^{2}\). Hence, the LEDs were mounted on the heat sink with a surface area of 60,000 mm\({}^{2}\), which is the optimum requirement. The right side of this figure shows the schematic diagram representing the p-i-n photodiode and its corresponding readout circuits. It shows the circuit diagram of the receiver designed using MCP606, low power, unipolar power supply of 5 V, rail to rail, phase retaining op-amp. The feedback resistor sets the required gain by considering the maximum reverse current of the photodiode. The desired output swing from 0 to 5 volts is achieved by the feedback resistor (R), which is computed using [PERSON]'s law by a ratio of voltage and photocurrent, i.e., 5-0 V/5 uA gives 1 M\(\Omega\). Theoretically, the feedback capacitor (C) limits the signal bandwidth from 0 Hz to 80 kHz (to capture the PRBS sequence and its harmonics with clock cycle 2 kHz) by C = \(\%\times\) pi \(\times\) R \(\times\) f. By experimental validation, a small feedback capacitor of 2 pF was added to reduce ringing oscillations caused by poles created due to output load [57]. Figure 9 shows the time delay measured using an oscilloscope between the reference PRBS signal and the received signal as the power is increased for blue light and the coherent bandwidth of the system. The absolute power at the receiver plane was recorded by a power meter by Thor Labs (PM100 USB). Using Equations (5) and (6), the delay spread (rms) of 5.97 us, mean delay spread of 70 us, and coherence bandwidth, \(B_{c}\) was found to be 33.5 kHz. The channel can be assumed to be flat-fading since \(B_{c}\) is significantly larger than the input signal bandwidth of 4 KHz.