Daylight as the only light source in the past was not considered only for its illumination in Iranian traditional architecture. The visual qualities and aesthetics of daylight were other considerations for architects. A good example of fantasy of daylight in Iranian architecture can be found in traditional houses. Diversity of different wall and ceiling openings is a testifier for this claim. To find out the effects of different design concepts in quality and quantity of light related to its specific space, a research has been conducted in Ameri House in Kashan with several central yards and spaces. Discovering the relation between architectural decisions and quality of daylight is the aim of this research. In this article the specifications of daylight in some spaces of this house are studied according to their location in the house, geometric shape of the place, location and condition of their openings related to their functions. Using luminance meter, the field data of several spaces were gathered and it was extended to a year by radiance simulation.
 Lighting Handbooks were used to analyse lighting conditions such as amount, uniformity or diversity of illumination, visual amenity and visual quality related to the function of the space. The information were analysed in four steps: 1- Room specifications: by calculating “Room Index”, “Room Depth Criteria”, “Perimeter Zone” and “Orientation Factor”. 2- Geometry and neighbourhood conditions: by drawing “No Sky Line” area, “Visible Sky Angle” in section and façade and “Shading Mask” of the window. 3- Analysing the field data: by drawing the “Illumination” contours in plan (on the reference height) and section of each room. 4- The illumination condition of each room in a whole year was simulated using Radiance Software. In steps 3 and 4, the data were analysed by “Useful Daylight Illuminance (UDI)”. It shows the percentage of the room area which is in “UDI Achieved” (100-2000 Lux), “UDI Autonomous” (300-2000 Lux), “UDI Supplementary” (100-300 Lux), UDI Exceeded” (> 2000 Lux), and “UDI Fell-Short” (< 100 Lux) in different months of the year in 9 am, 12 pm and 3 pm. At the end, the distribution of illumination in each room was calculated to determine the variation of the light pattern in two conditions of closed and open windows. It shows that according to this pattern, each room will be suitable for “visual interest” or “visual acuity” with regards to its function.
The results show that in Ameri House, daylighting design is performed in 4 levels. The first level is neighbourhood conditions; to decide about the relation of outdoor and indoor spaces in plan and section to have at least 40-degree “visible sky angle” for the main spaces. Second level is the specification of the main spaces and their adjacent rooms; that are located on the main axis of the yards with the best view and lighting condition. Third level is the depth and geometry of the rooms and details of the windows to help appropriate visual uniformity or diversity of illumination according to the function of the room. The depth of the room regarding to the height of the window is always less than the perimeter zone. It gives the architect the ability to choose the window details such as mesh frames and colour glazing to control the glare in front of the room without darkness problem in the further parts and have a better spread of illumination contours.
Fourth level is the interior layer spaces that have no direct access to daylight. In this case, different ceiling lighting systems such as “skylights”, “light scopes” and other systems are used to prepare daylight and natural ventilation simultaneously.
This study shows that, to have a good daylight pattern in buildings it is very important to take into consideration the daylighting system and strategies form the primary stage of design process (such as choosing mass and space, yards and spaces location, dimension and orientation toward the sun, sky view angle of the rooms and their openings) to the final detail stages (such as depth, dimension and details of the rooms and their openings) according to importance of the spaces related to their functions and accessibility.