https://community.infiniteflight.com/t/understanding-airport-markings/36959?u=zuhair.mazhar
“This graphic explains the difference from a ‘regular’ hold short line and the ‘IMC’ (Intrument Meteorological Conditions), hold short line which keeps the aircraft further back from the runway in LOW VIS conditions.”
“To keep things simple, IMC basically means when the weather is below minimums for VFR (Visual Flight Rule). In this case, for holding short (below 1200 ft AGL “Actual Ground Level”), visual minimums would be:
Daytime - 1 mile (statute) Visibility
Nighttime - 3 mile (statute) Visibility
If you cannot see an aircraft up to 1 mile out during the day and up to 3 miles out at night, that would be IMC weather.”
The ILS hold short line is used during IMC low visibility conditions, more than anything else.