I would like to draw the inference to the quote from Bilvastakam as below:
Indu vaare vratham sthithwaa niraahaarO mahEshwarah |
naktham hauShyAmi dhEvEshA Eka bilvam shivArpaNam ||
"Often we mistake "upavas" for "niraharam". While upavas is
establishing intimacy (mental) with the Lord, niraharam is fasting
which facilitates concentration and channelization of our energies.
The Dhramashastras prescribe both upavas and niraharam on
Shivarathri while giving concession for the old, the weak, the sick
and the diseased etc. It also advocates light food - "upAhAram" for
those who can be stable with little food.
Shasthras are really flexible and practical. We SHOULD adopt only
those tenets of shasthras that suits our body, family and social
conditions. Would it not be wise to eat something "satwik" and
worship the Lord happily instead of getting destracted by hunger ?
A more specific answer to your query would be that the tradition is
to fast completely during the day and night of Shivarathri, while
worshipping the Lord and breaking the fast the next day by partaking
food along with fellow devotees - called "pAraNam". This tradition
is still followed in rural areas where the social bondages are stillstrong." [Source Courtesy: Srinath Ram]
I would also like to quote the URL of 'Maha Shivarathri' website for more information here.