user47805: I have three light sensors  TSL2591, of signal I2C, that I need to connect (together) to an Arduino Mega. However, I'm not very sure of how share the SDA and SCL pins of the three sensors and I don't know how to change their address for the Arduino to read and show the data of each sensor. 
I have already read sensor's datasheet but there is not much information about this.

user6936: Looking at the datasheet, the TSL2591 does not appear to have a comfigurable address mechanism, therefore you are most likely obliged to use an I2C Multiplexer.
One example of such a device is the TCA9545A, Low Voltage 4-channel I2C and SMbus Switch With Interrupt Logic and Reset Functions, that can split one I2C line into 4 buses.

They are very easy to use and the pinout (and datasheet) are self explanatory.
Don't forget that you will need 3k3 Ω resistors on the INT, RESET, SDA and SCL lines from the Arduino and on each of the INTx, SDx, and SCx lines from the TCA9545A:


47805: <p>I have three light sensors  TSL2591, of signal I2C, that I need to connect (together) to an Arduino Mega. However, I'm not very sure of how share the SDA and SCL pins of the three sensors and I don't know how to change their address for the Arduino to read and show the data of each sensor. </p>

<p>I have already read sensor's <a href="https://cdn-shop.adafruit.com/datasheets/TSL25911_Datasheet_EN_v1.pdf" rel="nofollow noreferrer">datasheet</a> but there is not much information about this.</p>
 6936: <p>Looking at the datasheet, the TSL2591 does not <em>appear</em> to have a comfigurable address mechanism, therefore you are most likely obliged to use an I2C Multiplexer.</p>

<p>One example of such a device is the <a href="http://www.ti.com/lit/ds/symlink/tca9545a.pdf" rel="noreferrer">TCA9545A</a>, <em>Low Voltage 4-channel I2C and SMbus Switch With Interrupt Logic and Reset Functions</em>, that can split one I2C line into 4 buses.</p>

<p><a href="https://i.stack.imgur.com/EBsjG.png" rel="noreferrer" title="TCA9545A pinout"><img src="https://i.stack.imgur.com/EBsjG.png" alt="TCA9545A pinout" title="TCA9545A pinout"></a></p>

<p>They are very easy to use and the pinout (and datasheet) are self explanatory.</p>

<p>Don't forget that you will need 3k3&nbsp;&Omega; resistors on the <code>INT</code>, <code>RESET</code>, <code>SDA</code> and <code>SCL</code> lines from the Arduino <em>and</em> on <strong>each</strong> of the <code>INTx</code>, <code>SDx</code>, and <code>SCx</code> lines from the TCA9545A:</p>

<p><a href="https://i.stack.imgur.com/I3Kwy.png" rel="noreferrer" title="TCA9545A Typical Application Schematic"><img src="https://i.stack.imgur.com/I3Kwy.png" alt="TCA9545A Typical Application Schematic" title="TCA9545A Typical Application Schematic"></a></p>
