In stratus, with small SCWDs clear ice will form between 0ºC and -7ºC.   As it gets colder there will be mixed ice, clear and rime, with an increasing proportion of rime ice.   By the time the temperature gets down to -20ºC it will be only rime ice and, with more ice crystals mixed with the SCWDs in the cloud, the degree of icing will be light or, at worst, light to moderate.