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.

  • 1
    You may not put a sensor in direct sunlight. That is too bright and too hot. Only a solar cell can deal with direct sunlight. For the accurate number of lux, use a accurate sensor under a semi-transparent filter. Extra care should be taken that the sensor does not get too hot.
    – Jot
    Apr 22, 2019 at 3:13
  • I thing a simple LDR would work just as well. You won't get a nice calibrated LUX value, but you'd be able to compare different day and/or time, and see the difference in brightness.
    – Gerben
    Apr 22, 2019 at 14:28
  • PS the BH1750 can only measure up to 100000lx. That doesn't mean it can't handle more. It can, but will clip the value. The measurement also depends on the angle between the sensor and the sun as you can see in the graphs on page 3 of the datasheet. So you could aim the sensor slightly to the north, so the sensor values stay below the maximum value, and doesn't clip.
    – Gerben
    Apr 22, 2019 at 14:36
  • Maximum operating temperature for the BH1750FVI is 85 deg. Celsius.
    – Gerben
    Apr 22, 2019 at 14:39

2 Answers 2


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:


You can also use a LUX which is the advanced version of a LDR. Here is a tutorial:



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

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