value is 200 lux, daylight autonomy would give zero credit, while continuous daylight autonomy would give 0.5 credit (200/400 = 0.5). The benefit of continuous daylight autonomy is that it does not give a hard threshold of acceptable illuminance. Instead, it addresses the transition area—allowing for realistic preferences within any given space. For example, office occupants usually prefer to work at daylight below the illuminance threshold since this level avoids potential glare and excessive contrast. Useful illuminance Useful daylight illuminance focuses on the direct sunlight that falls into a space. The useful daylight illuminance calculation is based on three factors—the percentage of time a point is below, between, or above an illuminance value. The range for these factors is typically 100-2,000 lux. Useful daylight illuminance is similar to daylight autonomy but has the added benefit of addressing glare and thermal discomfort. The upper threshold is used to determine when glare or thermal discomfort is occurring and may need resolution. Illuminance distribution Besides determining how much illuminance is received on a horizontal surface, a method that analyses annual illuminance distributions for daylight has been developed. Every annual illuminance distribution is compared against each other using principal components analysis. This compares the relationship between each pattern. Daylight patterns that are more similar to each other due to architectural features and the time of the year the illuminance are produced are grouped together. Groups are used to form the most representative patterns for that given building. This method can be used to easily interpret how daylight is spread across the space throughout the entire year in any building. LEED documentation The LEED 2009 daylighting standards were intended to connect building occupants with the outdoors through use of optimal daylighting techniques and technologies. According to these standards, the maximum value of 1 point can be achieved through four different approaches. The first approach is a computer simulation to demonstrate, in clear sky conditions, the daylight illuminance levels 108-5,400 lux on, September 21 between 9:00 a.m. and 3:00 p.m. Another prescriptive approach is a method that uses two types of side-lighting, and three types of top-lighting to determine if a minimum of 75% daylighting is achieved in the occupied spaces. A third approach uses indoor light measurements showing that between 108-5,400 lux have been achieved in the space. The last approach is a combination of the other three calculation methods to prove that the daylight