  We first consider {\it deterministic} immersions of the $d$-dimensional
sphere into high dimensional Euclidean spaces, where the immersion is via
spherical harmonics of level $n$. The main result of the article is the, a
priori unexpected, fact that there is a uniform lower bound to the critical
radius of the immersions as $n\to\infty$. This fact has immediate implications
for {\it random} spherical harmonics with fixed $L^2$-norm. In particular, it
leads to an exact and explicit formulae for the tail probability of their
(large deviation) suprema by the tube formula, and also relates this to the
expected Euler characteristic of their upper level sets.
