How much PAR does sunlight provide?

[Pepere]

I am sort of curious if anybody has taken a par meter to a body of water outside and measured par at say 20 inches submerged in water at various times of the day and various cloud covers to see how much par is delivered that low…

Or if anyone has read something to give a feel.. granted it would vary with latitude and how close one was to a solstice or equinox…

 

[Pepere]

Well I found this:



Its not submerged but as much as 2500 PAR in Washington State around noonish in full sunlight…

 

[Anonymous_One]

Light is perhaps the only parameter we have in aquariums that is much lower than in nature. I used to make such measurements in nature with my own PAR meter, but I would have to track down the exact results somewhere. From what I remember, though, the normal irradiance in summer around noon is around 2000 PAR. However, even a small, translucent cloud in the sky can reduce this dramatically (to say 1000-1500 PAR). On a clear day, plants just below the water surface have roughly around 1000-1500 PAR available (depending on water clarity). But even the fastest growing aquatic plants (= aquatic weeds) can't use more than about 600-700 PAR (= light saturation), reaching half the photosynthetic rate at about ~125 PAR. In a number of scientific studies, scientists use irradiation of around 300-500 PAR when working with aquatic plants.

 

[Burr740]

I got 1900 on my back deck one time, not submerged. Dont remember time of day/year. I did angle it directly towards it