Davis VP2 Solar Radiation Sensor Spike

Wondering if anyone knows what causes the spikes in the solar radiation as shown in the graph below. I see this about the same time each day (9:30-10:30 AM) on clear days. Not a big deal, just curious. I’ll have to watch it throughout the year to see if the time of day changes. I’ve only been using the sensor since 1 Jan 2024. My first guess is that it’s a reflection from a window on my neighbors house. The windows reflect UV for home energy efficiency. The sun reflecting off the windows is extremely bright and you can feel the heat if you are in the path of the reflecting sun.

I think you’re correct it is a reflection of some sort even clouds can cause spikes, could be a combination.


Yesterday I noticed the sun was reflecting off the windows on the south side of my house onto the fence where the weather station is mounted. I didn’t see the reflection directly near the weather station but I think I was looking a couple of minutes too late. I’ll try to catch it at the right time today and take a photo. I know siting weather stations in a residential area is a challenge, especially for winds, but I never thought there could be an issue with the solar radiation sensor that has a clear view of the sky.

These sensors measure global solar radiation not direct so are susceptible to these effects. It’s normal and we have to accept it. All hobby sensors are like this. A Blake-Larsen one measures direct, if you can find one.


I think I found the source of the reflected sunlight. The sensor is mounted on the right side of the rain gauge, which is on the southeast side of the ISS, which is facing direct south. At about 9:30 AM, the sun is in the southeast sky, so the sunlight reflecting off of the metal pole shines directly onto the sensor until the sun moves further west and is no longer aligned with the pole and sensor.

To test my theory, I’ll put some dark tape along the pole on the southeast side. I suppose I could paint the pole flat black if the tape proves to mitigate the reflection.

Or, I think you can mount the sensor up with the anemo?

That’s where mine is…way up in the sky with nothing but birds and planes (and UFOs if any pass this way) to block the sun.

Same, up with the anny at the top of pole above my roof.

Thanks for the advice guys. I never thought about mounting the sensor at the top of the pole - I just mounted it where the Davis hardware accommodates it.

I would like to know when a UFO is blocking the sun though!