This works fine:
Code:
lipc-set-prop com.lab126.system sendEvent "; DISPLAY=:0 /usr/bin/xtestlab126 -d &"
So,
sh -c part is optional; to pass over blocking call use "&";
xtestlab126 specifically requires DISPLAY to being set.
/usr/bin prefix is optional, but it's better to use absolute paths. As
Aeris noted, execution environment is a bit different then default.
UPD: and
/usr/bin/light.sh just invokes
xtestlab126 -l.