The term "radiates light" refers to the emission of light energy from a substance. When a substance is heated to a high temperature, it begins to emit light, a phenomenon known as incandescence.
Option 1: Luminescent refers to the ability of a substance to emit light without heating. It includes both fluorescence and phosphorescence, but heating is not necessary for luminescence to occur.
Option 2: This is the correct answer. Incandescence specifically refers to the emission of light when a substance is heated to a high temperature.
Option 3: Fluorescence is the emission of light by a substance when it absorbs light of a shorter wavelength and re-emits light of a longer wavelength almost immediately. Fluorescence does not require high temperatures.
Option 4: Phosphorescence is similar to fluorescence, but with a delay in the emission of light. After exposure to light, a phosphorescent substance continues to emit light for some time even after the light source is removed. Phosphorescence does not require high temperatures.
In conclusion, the correct answer is option 2 (Incandescent), as it specifically refers to the emission of light from a substance when heated to a high temperature.