# Superposition of light waves of different colors

Can someone please assist? My question is regarding visible light. If, for example, red light and blue light are waves of different wavelengths and frequencies then how do they combine with all the other em waves on the visible spectrum to produce one wave of visible light? If waves of varying frequencies blend together then couldn’t all waves on the spectrum do so? I probably have a fundamental misunderstanding but I can’t seem to get my head around it.

• What do you mean by "one wave of visible light"? Visible light from the Sun or a typical light bulb is a mixture of waves of many frequencies. – PM 2Ring Mar 3 at 11:25

In some way this is similar to sound. The eardrum moves in response to the total sound pressure of all incoming waves. Then the ear does a kind of analog Fourier analysis, splitting the signal in different frequencies, mapped to different nerve cells in the auditory nerve.

The eye filters the total electric field by different pigments in different visual receptors (the cones). Some of these cone cells respond primarily to frequencies in the red, others to blue, others to green.

• Hi Pieter, that really helps, thanks. I’m just starting to get my head around these concepts. Is this similar to how a modulator and demodulator, fsk and telephone work? There is a communication protocol known as HART, where they send a 4-20mA signal through one wire but they also send digital information using fsk without affecting the 4-20mA signal in anyway. It seems that all information will be a current of some value so I struggle to see how this would not affect the overall current in the wire I.e affect the 4-20mA signal. Any assistance would be appreciated? – Blob Mar 8 at 11:38
• @Blob Yes, frequency-shift keying (I had to look that up, not my field) is like a melody with two notes, but the signal processing is accomplished by analog or digital electronics in some ways. Electronic filters can separate different frequency bands. – Pieter Mar 8 at 14:22

Electromagnetic fields add with superposition, meaning that the field at a certain point in space is the sum of all present field components. We'd have a single resulting field with with different spectral component.

For example sunlight contains the visible light that we can observe but also contains UV-components which are very much there, but we can still see them.

Theoretically all waves on the electromagnetic spectrum can blend together in this way since the principle of superposition applies.

• Hi Dakkvader, thanks for the response. So I take it we have the capacity to unblend them on arrival? – Blob Mar 8 at 12:12
• The field which we have at arrival is simply one field, which contains components of all the original fields since they add by addition. Depending on how one detects this field, the different components could be distinguished. If the wavelengths are suitable, a spectrometer could be used. If instead we have antennas, antennas are designed for a specific wavelength. When a field of different components are incident on it, each component have a different response. – DakkVader Mar 8 at 17:23
• The antenna may have a gain of 20dB for wavelength X and 3dB for wavelength Y. The field is one entity, i wouldn't say that they can be separated, but one can be distinguished. One could use a waveguide as a filter for example to guide radiation above a certain threshold frequency. So TLDR; With suitable techniques and methods, different field components can be detected, but splitting it up into it's respective components is not impossible, but difficult. Filtering certain components out is easier. @Blob – DakkVader Mar 8 at 17:25