We show that laboratory experiments can not measure the absolute value of dark energy .
All known experiments rely on electromagnetic interactions .
They are thus insensitive to particles and fields that interact only weakly with ordinary matter .
In addition , Josephson junction experiments only measure differences in vacuum energy similar to Casimir force measurements .
Gravity , however , couples to the absolute value .
Finally we note that Casimir force measurements have tested zero point fluctuations up to energies of \sim 10 \textrm { eV } , well above the dark energy scale of \sim 0.01 \textrm { eV } .
Hence , the proposed cut-off in the fluctuation spectrum is ruled out experimentally .