Solar control glass is manufactured by vapour-depositing metallic or metal-oxide coatings onto the glass surface or by tinting the glass mass. The key performance value is the g-value (total solar energy transmittance), which indicates how much solar energy passes through the glass into the room. Low g-values, typically between 0.2 and 0.5, reduce summer heat gain. High-quality selective coatings achieve good daylight transmittance combined with a low g-value. Solar control glasses are frequently combined with low-emissivity thermal insulation function, allowing a multiple-pane insulating glass unit to meet both requirements. The visible light transmittance should be aligned with daylighting and artificial lighting planning.