Light Pollution is a general term which encompasses Sky Glow, Light Trespass, Glare and Building Luminance as referred to in the Institution of Lighting Professionals guidelines.

Light Pollution is important for gaining planning permission where a development has bright lighting (eg stadium flood lighting) emanating into sensitive receptors such as bedrooms and ecologically dark places. 

Sky Glow is the brightening of the of the night sky over our towns, cities and countryside. This can be quantified by measuring the maximum permitted percentage of luminaire flux for the total installation that goes directly into the sky. 

Light Trespass is the spilling of light beyond the boundary of the Development. This is assessed using vertical luminance in lux (Ev) measured flat on the glazing at the centre of the window.