Logging haproxy check results / problems

how can I enable logging of haproxy check results (or failures only)? I've seen some mailing list posts suggesting this is possible:

Server LDAPSFarm/LDAPS1 is DOWN, reason: Socket error, check duration: 277ms. 1 active and 0 backup servers online. 0 sessions requeued, 0 total in queue.

but I don't get the same results. My config is more of less this:

global
        log 127.0.0.1 local0
        user haproxy
        group haproxy
        spread-checks 5

defaults
        log     global
        mode    http
        option  httplog
        option  dontlognull
        retries 3
        redispatch
        maxconn 2000

        stats enable
        stats hide-version

        option allbackups

listen XXX YYY
        mode tcp
        balance roundrobin
        option httpchk /

        server XXX-1 ZZZ1 check port 8080 inter 2s rise 15 slowstart 10s
        server XXX-2 ZZZ2 check port 8080 inter 2s rise 15 slowstart 10s

If I enable statistics page and look at it, I can see that sometimes server lines go yellow/red which suggests monitoring failures, but currently I don't see anything related in the log files. How can I get this information?