ISO 15871:2019 specifies requirements for indicator lights to show the status of freight-container-handling spreaders and grappler arms.It is applicable to:a) container-handling spreaders with twistlocks for handling unladen and/or laden freight containers;b) grappler (bottom lift) arms for handling semi-trailers and swap bodies;when fitted to:— counterbalance lift trucks, with masts, as defined in ISO 5053-1:2015, 3.3;— rough terrain trucks, with masts, as defined in ISO 5053-1:2015, 3.7;— non-stacking low-lift straddle carriers, as defined in ISO 5053-1:2015, 3.18;— stacking high-lift straddle carriers, as defined in ISO 5053-1:2015, 3.19;— variable-reach trucks, as defined in ISO 5053-1:2015, 3.20;— rough-terrain variable-reach trucks, as defined in ISO 5053-1:2015, 3.21;— variable-reach container handlers, "reach stackers", as defined in ISO 5053-1:2015, 3.23;— counterbalance container handlers, as defined in ISO 5053-1:2015, 3.24.