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Technical Articles

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Energy Efficiency for Indoor Lighting Projects

Out of the energy consumed around the world, about 19% is used for lighting. This percentage is higher if we focus on the use of lighting in buildings, where it can even reach up to 40%.

The way to reduce this consumption is not to give up quantity or quality of the light, because this would affect people’s comfort and well-being. The solution is to use more efficient lighting systems.

This efficiency will depend on several factors. These are the most important:

•    Design of the luminaire: both the reflector and the body of the luminaire must be designed so that an optimum use of its performance and luminous flux is made, avoiding annoying glare and not forgetting visual comfort.

•    Lamp that is used: when choosing the type of lamp to be used, we must take into account its colour rendering, its useful life, the possibility of adjusting it and above all, its energy efficiency [lumen/Watt]. Some types of lamps are labelled according to their efficiency with letters from A to G.

•    Auxiliary equipment: it limits the maximum losses of systems. Electromagnetic systems with high or moderate losses are forbidden by several directives. This equipment will gradually disappear in favour of electronic equipment that offers more advantages and saves more energy.

•    Control and adjustment systems: using adjustment systems that adapt, for example, to the times the different spaces are used, or to the presence of natural light, or which have presence detectors. Up to 60% of energy can be saved.

•    Use of natural light: nowadays artificial light can be complemented with natural light, or vice versa, with an adjustment system of artificial light, depending on the natural light that is available. This saves a lot of energy in some cases.

•    Maintenance of the installation: as time goes by, the performance of the installation decreases, either because the lamps lose flux or because the performance of the luminaires decreases because the reflector wears out, or dirt gets accumulated.  In order to avoid this loss of energy as much as possible, a maintenance plan for the installation would be needed, as well as a calendar to replace the lamps according to their nominal life, even if they still work, because after that established period of time their flux will decrease considerably.

The state government has brought out several regulations with the aim of limiting energy consumption. Regarding indoor lighting, the Spanish Technical Building Code (CTE) is the regulating legal framework for energy efficiency in lighting installations.  

The CTE was approved by Royal Decree 314/2006 of 17 March 2006 and aims to make building more sustainable by establishing requirements relating to safety and habitability. It affects residential, commercial, educational, health, sports, industrial and sociocultural buildings.

It includes several basic documents that refer to safety, structures, heating/air conditioning issues, etc. The most innovative one is the one on Energy Saving (DB HE), with the aim of using energy in a more rational way in buildings. It includes energy efficiency criteria and the use of renewable energies. Section HE3 refers to lighting and it is the first regulation that refers to energy criteria, because, for example, in the UNE EN 12464-1 standard, only the minimum values for quantity and quality of lighting in indoor work areas are regulated, but the efficiency of the installation is not mentioned.

In order to assess energy efficiency, the Building Technical Code defines the VEEI (Value of Energy Efficiency of the Installation) as follows:

VEEI

where P is the total power installed, that is, the power of the lamp and the power consumed by auxiliary equipment that it requires in order to be used [W]; S is the lit-up surface [m2] and Em is the average horizontal illuminance maintained [lux] and is defined as the value under which the average illuminance on the specified surface cannot drop, regardless of the age or condition of the installation. This last value must be at least the one established by the different UNE standards, for example, the aforementioned UNE EN 12464-1 in the case of indoor work.  We will obtain these values from the different light calculation programmes that exist on the market. In order to take into account how the light of luminaires and lamps will decrease over time, a maintenance factor must be applied to the calculation, normally 0.8 in the case of standard indoor installations, which will give a higher measurement for the installation taking into account that loss of performance after the installation is made. Once the VEEI of an implementation suggested in a project is calculated, with luminaires and a specific distribution of these, we must check that this value is never higher than the limit value established in the CTE tables, according to a classification for different activities.

Marta Culubret
Project Department Manager