I'm pregnant and last night experienced white flashes in eyes, what can it be?

So last night I saw white flashes in my eyes.
The only issue is is that I don’t know if it was in my eyes or outside.
My blood pressure has been good – last reading was a month ago – I’m 21 weeks pregnant. I’ve read it can be a sign of preeclampsia, however I have no other symptoms and believe to be generally healthy.
I will see tonight if my partner sees the white lights as he was not here last night.
Does anyone know if preeclampsia makes you see white flashes only at night?
Wouldn’t you see it all through the day as well if this were the case?
I am going to see my obyn next week but thought maybe someone here might know?

Thanks
x