Coaxing the right amount of natural light into buildings is both an art and a science. The challenge is getting lightwell into the inside of a building and at the same time eliminating glare, minimizing thermal loss, reducing solar heat gain, preventing downdrafts, and improving resistance to condensation.

• Eliminating glare: Natural sunlight, while important and beneficial to living, working, and learning environments, can also cause serious problems in terms of debilitating solar glare and overheating. The Green Building's Council LEED standard requires that "no direct sunlight be admitted to critical task areas in order to be considered as daylit." Hence, architects seek to maximize the penetration of diffuse light while blocking direct sunlight.
  
  
• Minimizing thermal loss: Energy costs can be significant to heat or cool a building during certain times of the year. Glazing systems must be insulated to prevent against unnecessary and costly heat or cooling loss.
  
  With improved insulation, energy consumption is significantly minimized. Alternatively, by designing with improved insulation materials, smaller HVAC units can be designed to compensate for improved insulation.
  
  
• Reducing solar heat gain: In summer, comfort is based on reducing solar heat gain through glazing systems and by reducing the interior surface temperature. High R-value glazing will decrease the amount of direct radiation striking a person, lower the interior temperature, and improve comfort.
  
  
• Preventing downdrafts: In winter, indoor comfort is based on reducing downdrafts through glazing systems. Downdrafts are a result of air near the glazing becoming cool and dropping to the floor. It is then replaced by warmer air from the ceiling, which in turn is cooled, creating a convective loop. This sets up an air movement pattern that feels drafty and accelerates heat loss.
  

• Resistance to condensation: Buildings with low R-value glazing suffer from water condensation caused by the formation of frost on the inside surface of the glass in winter. This condition is caused by the glazing surface temperature dropping below either the outdoor dew point or the indoor frost point. Excessive condensation can contribute to:
• • Growth of mold and mildew
  • Damage to interior surfaces and glazing frames