user55850: I'm trying to measure how bright the day is on a particular day to see how it affects plant growth. The brightest sun can be 120,000 lux. It possible to measure such a large brightness? What sensor do I use?
The best options I've found is the BH1750FVI since its sheet says, "[i]t is possible to detect min. 0.11 lx, max. 100000 lx"
However, it still doesn't go high enough.
Note: I live "only" 3,494 km (2171 miles) from the equator, and it can get fairly bright here.

user85442: What about SiLabs SI11xx Sensors? Some of them are designed for direct sunlight.

user67324: You can use a photo resistor. It is also known as an  LDR (Light dependent resistors) and here is a great tutorial to do just that. You can also find a conversion from the 8-bit analog value to lumens if you wish. Here is a tutorial:
https://www.instructables.com/id/Measuring-Light-Using-Light-Sensor/
You can also use a LUX which is the advanced version of a LDR. Here is a tutorial:
https://www.instructables.com/id/How-to-Measure-LUX-With-Arduino/

55850: <p>I'm trying to measure how bright the day is on a particular day to see how it affects plant growth. The brightest sun can be <a href="https://en.wikipedia.org/wiki/Daylight" rel="nofollow noreferrer">120,000 lux</a>. It possible to measure such a large brightness? What sensor do I use?</p>

<p>The best options I've found is the <a href="https://www.mouser.com/ds/2/348/bh1750fvi-e-186247.pdf" rel="nofollow noreferrer">BH1750FVI</a> since its sheet says, "[i]t is possible to detect min. 0.11 lx, max. 100000 lx"</p>

<p>However, it still doesn't go high enough.</p>

<p><strong>Note:</strong> I live "only" 3,494 km (2171 miles) from the equator, and it can get fairly bright here.</p>
 85442: <p>What about SiLabs SI11xx Sensors? Some of them are designed for direct sunlight.</p>
 67324: <p>You can use a photo resistor. It is also known as an  LDR (Light dependent resistors) and here is a great tutorial to do just that. You can also find a conversion from the 8-bit analog value to lumens if you wish. Here is a tutorial:</p>
<p><a href="https://www.instructables.com/id/Measuring-Light-Using-Light-Sensor/" rel="nofollow noreferrer">https://www.instructables.com/id/Measuring-Light-Using-Light-Sensor/</a></p>
<p>You can also use a LUX which is the advanced version of a LDR. Here is a tutorial:</p>
<p><a href="https://www.instructables.com/id/How-to-Measure-LUX-With-Arduino/" rel="nofollow noreferrer">https://www.instructables.com/id/How-to-Measure-LUX-With-Arduino/</a></p>
