The height read-only property of the SVGFESpecularLightingElement interface describes the vertical size of an SVG filter primitive as a SVGAnimatedLength.
It reflects the height attribute of the <feSpecularLighting> element, which lights a source graphic using the alpha channel as a bump map. The attribute is a <length> or a <percentage> relative to the height of the filter region. The default value is 100%. The property value is a length in user coordinate system units.
const feSpecularLighting = document.querySelector("feSpecularLighting");
const verticalSize = feSpecularLighting.height;
console.log(verticalSize.baseVal.value); // the `height` value