Sunny Aurora ?

[bens_dad]

I guess that an Aurora may be visible at dawn or dusk, but I had an alert:

11th August 2024 3:00pm
Aurora is likely to be visible from Scotland, northern England and Northern Ireland

.

Right now it is very sunny: my light meter app says 300-400 thousand Lux
- that is a thousand times as bright as it is indoors.

Actually, if I read the aurora alert site's FAQ they do explain why they issue alerts in the daytime.

Comments

[crazyscot]

That light meter reading seems suspicious...? Direct sunlight is supposed to be around 32k-100k lux. I've seen readings around 75k here in NZ from direct mid-morning summer sun, albeit on an uncalibrated device.

[bens_dad]

This was with an uncalibrated phone app, so could easily be wildly out. My previous phone maxed out at 50k lux.

The strongest reading did appear to come at an unexpected angle. I wonder whether the protective glass over-screen was somehow focusing light onto the sensor, increasing the reading ?

https://www.extrica.com/article/21667 concludes with:
An engineering rule of thumb is 120 lx equals 1 W/m2, or 1 Sun equals 120000 lx.
[1 Sun = 1kW/m^2]

At best we got 100W/m^2 from our solar panels in Cambridge (1-2 hour average production) which were supposed to be 14% efficient, which gives about 84k lux.

So, I wont trust the absolute readings from this app. Thanks.