Daylighting is the practice of placing windows, skylights, other openings, and reflective surfaces so that direct or indirect sunlight can provide effective internal lighting. Particular attention is given to daylighting while designing a building when the aim is to maximize visual comfort or to reduce energy use. Energy savings can be achieved from the reduced use of artificial (electric) lighting or from passive solar heating. Artificial lighting energy use can be reduced by simply installing fewer electric lights where daylight is present or by automatically dimming or switching off electric lights in response to the presence of daylight – a process known as daylight harvesting.
The lux is the unit of illuminance, or luminous flux per unit area, in the International System of Units (SI). It is equal to one lumen per square metre. In photometry, this is used as a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface. It is analogous to the radiometric unit watt per square metre, but with the power at each wavelength weighted according to the luminosity function, a model of human visual brightness perception, standardized by the CIE and ISO. In English, "lux" is used as both the singular and plural form. The word is derived from the Latin word for "light", lux.
A light meter is a device used to measure the amount of light. In photography, an exposure meter is a light meter coupled to either a digital or analog calculator which displays the correct shutter speed and f-number for optimum exposure, given a certain lighting situation and film speed. Similarly, exposure meters are also used in the fields of cinematography and scenic design, in order to determine the optimum light level for a scene.
The Kruithof curve describes a region of illuminance levels and color temperatures that are often viewed as comfortable or pleasing to an observer. The curve was constructed from psychophysical data collected by Dutch physicist Arie Andries Kruithof, though the original experimental data is not present on the curve itself. Lighting conditions within the bounded region were empirically assessed as being pleasing or natural, whereas conditions outside the region were considered uncomfortable, displeasing or unnatural. The Kruithof curve is a sufficient model for describing pleasing sources that are considered natural or closely resemble Planckian black bodies, but its value in describing human preference has been consistently questioned by further studies on interior lighting.
Lighting or illumination is the deliberate use of light to achieve practical or aesthetic effects. Lighting includes the use of both artificial light sources like lamps and light fixtures, as well as natural illumination by capturing daylight. Daylighting is sometimes used as the main source of light during daytime in buildings. This can save energy in place of using artificial lighting, which represents a major component of energy consumption in buildings. Proper lighting can enhance task performance, improve the appearance of an area, or have positive psychological effects on occupants.
In photography, exposure value (EV) is a number that represents a combination of a camera's shutter speed and f-number, such that all combinations that yield the same exposure have the same EV. Exposure value is also used to indicate an interval on the photographic exposure scale, with a difference of 1 EV corresponding to a standard power-of-2 exposure step, commonly referred to as a stop.
Window coverings are considered any type of materials used to cover a window to manage sunlight, privacy, additional weatherproofing or for purely decorative purposes.
When setting photoflash exposures, the guide number (GN) of photoflash devices is a measure photographers can use to calculate either the required f‑stop for any given flash-to-subject distance, or the required distance for any given f‑stop. To solve for either of these two variables, one merely divides a device's guide number by the other.
Architectural lighting design is a field of work or study that is concerned with the design of lighting systems within the built environment, both interior and exterior. It can include manipulation and design of both daylight and electric light or both, to serve human needs.
Daylight is the combination of all direct and indirect sunlight during the daytime. This includes direct sunlight, diffuse sky radiation, and (often) both of these reflected by Earth and terrestrial objects, like landforms and buildings. Sunlight scattered or reflected by astronomical objects is generally not considered daylight. Therefore, daylight excludes moonlight, despite it being reflected indirect sunlight.
Glare is difficulty of seeing in the presence of bright light such as direct or reflected sunlight or artificial light such as car headlamps at night. Because of this, some cars include mirrors with automatic anti-glare functions and in buildings, blinds or louvers are often used to protect occupants. Glare is caused by a significant ratio of luminance between the task and the glare source. Factors such as the angle between the task and the glare source and eye adaptation have significant impacts on the experience of glare.
Often task lighting refers to increasing illuminance to better accomplish a specific activity. However, the illuminance level is not the only factor governing visibility. Contrast is also important, and a poorly positioned light source may cause contrast reduction, resulting in loss of visibility. The most important purpose of task lighting in the office is not increasing illuminance, but improving contrast. General lighting can be reduced because task lighting provides focused light where needed.
Architectural design optimization (ADO) is a subfield of engineering that uses optimization methods to study, aid, and solve architectural design problems, such as optimal floorplan layout design, optimal circulation paths between rooms, sustainability and the like. ADO can be achieved through retrofitting, or it can be incorporated within the initial construction a building. Methods of ADO might include the use of metaheuristic, direct search or model-based optimisation. It could also be a more rudimentary process involving identification of a perceived or existing problem with a buildings design in the concept design phase.
Light effects on circadian rhythm are the effects that light has on circadian rhythm.
In lighting design, the lumen method,, is a simplified method to calculate the light level in a room. The method is a series of calculations that uses horizontal illuminance criteria to establish a uniform luminaire layout in a space. In its simplest form, the lumen method is merely the total number of lumens available in a room divided by the area of the room. In order to perform this calculation, many factors, coefficients, lamp lumen data and other quantities must be gathered. Despite the scientific impression of the lumen method equations, there are inaccuracies and assumptions built into the method. Therefore, the lumen method should not typically be used as a standalone, final solution; it should be used as a tool in particularly uniform settings of lighting design if a simple, rough technique of illuminance quantification is desired.
Daylight harvesting systems use daylight to offset the amount of electric lighting needed to properly light a space, in order to reduce energy consumption. This is accomplished using lighting control systems that are able to dim or switch electric lighting in response to changing daylight availability. The term Daylight Harvesting has become the standard in the fields of lighting, sustainable architecture, and active daylighting industries.
Sustainable lighting is lighting designed with energy efficient light sources. "There are simple design strategies and some materials that can facilitate the energy saving advantages of natural light. Light colored interiors and open floor plans are good choices. This approach also augments artificial light efficiency. Energy efficient lighting is not simply finding the most light for the least wattage or the longest lasting light bulb. Proper sizing of the light to the needs of the location and the tasks that will be performed, called task lighting, is an energy saving strategy."
In architecture, a daylight factor (DF) is the ratio of the light level inside a structure to the light level outside the structure. It is defined as:
The artificial sky is a daylight simulation device that replicates the light coming from the sky dome. An architectural scale model or 1:1 full-scaled aircraft is placed under an artificial sky to predict daylight penetration within buildings or aircraft that subjects to different situations, complex geometries, or heavily obstructed windows. The concept of the artificial sky was derived due to heliodon’s limitation in providing a stable lighting environment for evaluating the diffuse skylight component.
