What colour will the lamp appear if you look at it though a green filter?

When you look at a lamp through a green filter, the lamp will appear green if it emits green light or reflects green wavelengths. If the lamp emits other colors, such as red or blue, those colors will be filtered out, making the lamp appear dark or black, as the green filter only allows green wavelengths to pass through. Thus, the perceived color depends on the light source's color and the filter's properties.