In physics, each individual light source typically emits a range of wavelengths, rather than a fixed wavelength. This is due to the inherent nature of light and the way it is produced. For example, an incandescent light bulb emits a broad spectrum of wavelengths, ranging from infrared to visible light to ultraviolet. Similarly, a fluorescent light tube produces a range of wavelengths corresponding to the different phosphors used in the tube.
However, there are certain situations where a specific wavelength can be produced or isolated. This is commonly achieved through the use of specialized devices such as lasers or filters. A laser is designed to emit coherent light of a specific wavelength, resulting in a narrow and well-defined spectral line. Optical filters can also be employed to transmit or block specific wavelengths, allowing only certain portions of the spectrum to pass through.
So, in general, individual light sources emit a range of wavelengths, but there are techniques available to generate or select specific wavelengths when needed.