PROJECT DESIGN ENGINEER
Lighting, according to the definition of CIE (International Commission on Illumination) is the light application designed to make visual perception for objects, their surroundings or a specific region. Basically, lighting is the control and application of light in a way that helps to see. Although the main purpose of lighting is to meet the need for vision, not every light applied for this purpose can provide comfortable vision. Adequate and high-quality light provides good vision and illumination, but also protects eye health by preventing the eye from getting tired quickly. In lighting applications, the spectral and photometric properties of light, the properties of objects such as light transmission, reflection and absorption, the ability of the human eye to see light, as well as the existing colors should be considered as a whole. In this context, if we should give examples for some lighting terms and definitions:
Light Intensity
It is the amount of light emitted by a light source in a certain direction. Its symbol is the letter I and its unit is Candela (cd). When a sphere with a radius of 1m is taken as an example, the intensity of the light source at the center of the sphere is the amount of light falling on a 1m² area on the surface of the sphere. This is the definition for “1 candela”.
Luminous Flux
It is the measure of the power of the total skylight, which reaches in all directions, not in a certain direction. Its symbol is Φ (fi) and its unit is lumen (lm). The luminous flux does not depend on the distance from the source, surface area or dimensions, but only on the power of the source. In this way, light sources can be compared according to light fluxes.
Glow
It is the amount of light intensity in a unit area emitted by a light source in a certain direction. It is also called “luminance”. Its symbol is the letter L and its unit is cd/m².
Level of Light
The unit illuminated by the light source is the amount of luminous flux falling on the surface. It is also called luminance. Its symbol is the letter E and its unit is lux (lx). Poor quality of lighting poses security risks in many areas in the sector. The level of brightness varies depending on the type of work to be done, the surface to be worked on, and the lighting needs of the worker. To reach a common ground on the amount of illumination in closed workplaces, the TS EN 12464-1 standard was determined by TSE (Turkish Standards Institute). This standard covers lighting rules for people in indoor workplaces that meet the visual comfort and performance needs of people with normal eye (visual) capacity. In this regard, Table 1 and 2 show the minimum amounts of luminance level in some working environments.
Contrast
This is the issue caused by the fact that the lighting levels are too different between the illuminated areas. The brightness level of the workplace should not be too different from the brightness level in other areas, otherwise distraction may occur. For this reason, large differences in illumination (or skylight) levels should be avoided.
UGR (Unified Glare Rating)
UGR, or unified glare rating, is actually an index created to mathematically indicate the glare effect according to the definition of CIE (International Lighting Commission). In this context, the maximum UGR values of the area to be illuminated are defined so as not to adversely affect eye health.
CCT (Correlated Color Temperature)
It is a method of describing the light color of a light-emitting source based on the temperature of a black mass that radiates at the same dominant frequency as the source. CCT describes the color appearance of light emitted by a source when heated to a certain temperature, relative to the color of light from a reference source, and is measured in Kelvin (K). The CCT value of lighting sources classifies the color of the light emitted, as warm, neutral and cool colors. Generally, 3200K and lower values are considered warm, 5000K and higher values are considered cold, and the values in between are considered neutral colors. The color temperatures of the products should be determined according to the lighting purpose and the places of use. The effects of warm or cold colors on people vary. Warm colors are generally relaxing and comforting, while cold colors are concentration enhancing. For instance, warm colors are often preferred in living rooms, bedrooms and restaurants, while cold colors are preferred in offices, hospitals and educational institutions. When designing lighting, the design should be made taking this into account.
Color Rendering Index (CRI)
CRI is the scale of reflection of colors of artificial light sources compared to natural light sources. The color of an object perceived by the human eye may vary depending on the skylight that affects it. Artificial light sources, such as sunlight, may not contain the full spectrum (i.e. all colors). In this case, objects are not perceived by the human eye in their true color. The CRI value indicates the level of proximity to the actual value. As this value between 0-100 increases, the degree to which the source reflects the true color of objects also increases. By choosing light sources with a high CRI value, the true colors of objects can be selected.
Glaring
A bright light source or its reflection has an effect on the human eye and allows the eye to adapt to that level of brightness. In this case, it becomes difficult to see the dark and low reflection areas of the objects in the environment or the work area. This condition is called “glaring”. In order to avoid glaring issues, the area to be illuminated should be provided with several lighting products with same power instead of one high-powered product, the light of lighting sources should be controlled using lenses or reflectors, and work surfaces should be created using less bright and low-reflection materials.
Luminous Efficiency
It is the value obtained by dividing the luminous flux emitted by a light source, by the power consumed by the source. It is the mathematical expression of the proportion of the consumed electrical power that is converted into light. It is also called the “activity factor”. Its symbol is the sign η and its unit is lumen/watt (lm/w). The skylight value requested or obtained in lighting applications is directly proportional to the power of the source. A strong source means excess skylight flux. However, it cannot be claimed that a light source whose power is higher than another source will always give more luminous flux. The important point here is the luminous efficiency of the source, that is, the amount of skylight it gives per unit watt. The sources are of the same power, and can give different luminous flux from each other. For instance, a standard bulb with a 40W incandescent wire gives an average of 400lm skylight, while a 40W LED bulb of the same power gives an average of 2800lm skylight. In addition to different product groups, even two products in the same group can also provide different skylights with the same powers. High efficiency products should be preferred in applications and energy efficiency should be increased by using higher luminous fluxes at lower powers. Today, lighting is ensured in accordance with different purposes by using different product groups together with the developing technology in many structures and areas that we use in our daily lives, such as factories, shopping malls, hotels, restaurants, streets and avenues, hospitals, parking lots, parks and gardens etc. At this point, in order to provide the most accurate lighting from an ergonomic point of view, first of all, a design should be provided in such a way that it is suitable for the lighting purpose. The purpose of lighting should be determined and the design should be made by assessing all the parameters such as how much natural light sources are used, the luminance distributions of the light sources to be used and the color rendering values of these products on objects, the light reflection and absorption values of the structures and objects in the areas, the glare measures caused by the luminance directly affecting the human eye, the homogeneous distribution of light sources, as well as the energy efficiency.
