In 1964 Grunbaum conjectured that any primitive set illuminating from withi
n a convex body in E-d, d greater than or equal to 3, has at most 2(d) poin
ts. This was confirmed by V. Soltan in 1995 for the case d = 3. Here we giv
e a negative answer to Grunbaum's conjecture for all d greater than or equa
l to 4, by constructing a convex body K subset of E-d with primitive illumi
nating sets of an arbitrarily large cardinality.