It sounds like you need a logical switch with the "and" operator.

LS#1 operator A>X, Source (A) is RS, X=-90 (that's when RS is 5% above -100)

LS#2 operator A>X, Source (A) is S2, X=-90 (that's when S2 is 5% above -100)

LS#3 Operator AND, Value 1 = LS#1, Value 2 = LS#2

LS#3 becomes positive only if both LS#1 and LS#2 are positive.

Use LS#3 as the source to activate your landing lights.