This kind of thing can be okay for progressive checking. I normal dislike this style of code/logic but it seems a good fit for this kind of problem.

if ( $range > 500 )
{
    WAT_OP();
}
elsif ( $range >= 425 )
{
    some_op();
}
elsif ( $range > 400 )
{
    some_other_op();
}
elsif ( $range > 300 )
{
    exit 0;
}
else
{
    complete_tree_op();
}
[download]

You can also do something more dispatchy–

my @action_tree = ( { test => sub { $_[0] >= 300 && $_[0] <= 400 },
                      action => sub { print "GUDNITES\n"; CORE::exit(0
+) } },
                    { test => sub { $_[0] >= 425 && $_[0] <= 500 },
                      action => sub { print "OHAI\n" } } );

while ( my $signal = <SIGNAL_SOURCE> )
{
    $_->{test}->($signal) && $_->{action}->() for @action_tree;
}
[download]

I'm not advocating either, or that second style of terseness, or any style or approach for that matter. Just expanding the library of options. :P

Thanks YourMother! This approach worked as expected and with narrowing down the numbers being sent out by the serial monitor I can fine tune the range of the photo resistor to accomplish what I need it too. Thanks to all who answered.