Coherent lie sources. Visible light waves have an abnormally short wavelength, by example of a red light has a length of about 650 nanometers. in context, there are 1 billion that nanometers in a meter illustrating this point. This highlights the miniscule difference between wavelengths of constructive or destructive interference. The observational effects of interference for the visible light waves are so difficult to observe that we must as designers understand that and the principles behind them. So considering that selecting the correct light sources, must also be coherent by a factor of 50 nanometers highlights the difficulty in making the right choice between two light sources.

The two light sources that maintain a consistent phase difference with each other is said to be coherent light sources at a micro scale. At a design scale, this is defined by selecting complimentary light bulbs with the same intensity and Lux levels. Consider two light sources producing artificial light waves at the same frequency, but one source is direct and focused while another has a destructive high Lux level emanating from a point source focus light. Such light sources are said to be not in the same phase in their cycle of light production. And they are said to be out of phase. Even if the light sources are not similar in the type of Light distribution, as long as the amount of luminosity they emit remains the same and in context with each other, the light sources are said to be coherent.

Artificial light sources such as incandescent light bulbs have an intrinsic irregularity associated with the manner in which they produce light. The production of light results when atoms of the filaments or source become electrically excited and produce an electric magnetic Lightwave. Since the movement of atoms is unpredictable, the light waves they produce are automatically out of phase. However, there is no possibility that the human eye will ever become aware of this pattern because of the nanometer scale at which it is happening. The important As I design factor is to select a stable and unchanging source of light. This is essential that any selected sources of light be coherent and in the same phase with each other