The intensity (I) of sunlight is related to the energy density by the formula:
\[
I = \frac{1}{2} c u
\]
where \( c \) is the speed of light in a vacuum (\( c \approx 3 \times 10^8 \, \text{m/s} \)). Rearranging the formula to solve for \( u \):
\[
u =
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