It is useless to build a facility that costs millions of dollars only to have its useful life cut short by the growth of a new city. For amateur astronomers the problem of light pollution becomes a nightmare. Apart from the simple pleasure of looking at the night sky, the work of some amateurs supplements the work of professionals. These amateurs should be regarded as unpaid professional observers. The main function of a telescope is to amplify light from distant objects, as these objects are very faint.
Stray light has the effect of washing out the contrast and reducing the image quality.
If you turn up the brightness on your TV you can simulate the effect. The higher the brightness the more the image deteriorates. For an astronomer, that light YOU leave on in the back yard, or those flood lights in the driveway, can mean the end to any chance of using a telescope on all but the brightest of objects. The big problem with most lighting is poor design or bad layout. Most domestic lighting is improperly shielded and spreads light in all directions, casts shadows, makes blind spots and puts very little illumination where it is needed.