Even though LEDs have proved their worth as energy efficient solution to lighting, the decades-old investment in conventional lighting fixtures has delayed their large-scale implementation. For the past few years, several of these legacy systems have started approaching their end-of-life, meaning they are being replaced by new technologies such as LEDs.
Codes and Standards
The ongoing evolution of lighting systems requires engineers to stay up-to-date with modern regulations, codes and guidelines. The global trend towards energy efficient products has greatly influenced the design of lighting fixtures, particularly after the adaptation of LED lighting. System Integrators and designers are facing challenging requirements from their clients for low-maintenance & high-efficiency systems.
Consultants often rely on codes and guidelines put forth by organizations such as ASHRAE and International Energy Conservation Code (IECC) to determine the energy efficiency measures that must be implemented. In addition to these codes, some countries/states also have strict regulations such as Title 24 in California that require designs to be even more stringent.
Both ASHRAE 90.1 and IECC define the lighting-power allowance and lighting-power density for fixtures, values of which can be calculated either through the space-by-space or building area method, as per the designer’s choice. Furthermore, these requirements also define the need for lighting controls, i.e. automatic daylight-responsive controls, vacancy sensors and bi-level lighting.
These guidelines are supplemented by emergency lighting codes given by NFPA 101: Safety Code that incorporates the backup requirements for fixtures. There are various code classifications according to the lighting application, e.g. wastewater treatment, which should be taken into account by the consultant while designing the illumination system.
The final resource for lighting scheme designers and consultants is the Illumination Engineering Society (IES) Lighting Handbook that presents itself as a reference handbook, containing all major literature resources in one place.
A major factor influencing lighting calculations is light-loss factor, or LLF, that gives insight into the differences between laboratory and real-world illumination conditions. They are divided into two factors:
- Nonrecoverable – e.g. ambient temperature and voltage to luminaire factors that cannot be controlled by the end user through maintenance
- Recoverable – are influenced through timely maintenance
Other elements that need to be considered are the uniformity rations, i.e. maximum-to-minimum and average-to-minimum foot-candle for uniform lighting designs. These ratios are defined in tables found in Chapter 21 – 37 of the IES lighting handbook.
Choosing Fixture Types
Selecting the proper fixture type ensures that the right level of illumination is obtained while at the same time energy efficiency and comfort are kept to a maximum. The flexibility of arrangement of individual diodes within LED fixtures allows the lighting requirements to be met in a precise manner.
Most owners expect their LED lighting system to be maintenance-free for at least 10 years, which is why choosing the right fixture type is important. For consultants and designers who are working in existing facilities, additional factors must be taken into account. If corrosion is detected, then a fixture that has moisture protection needs to be installed in order to fulfill the clients’ requirement for maintenance-free installation. This should be followed by taking color temperature into account so that it matches with the one used at the rest of the facility.
Once these factors have been considered, the codes and references can be reviewed, and lighting layouts can be designed.
Calculations and Energy Analysis
Lighting calculations can be carried out by hand or through computer software. Lumen and zonal cavity methods are used for hand calculations while software such as AGi32, Visual Lighting 2017, Autodesk Revit, etc. can be used for large-scale calculations.
After the lighting design has been finalized in accordance with the owner’s requirements and local codes, the US Department of Energy’s COMcheck assesses the scheme. A final report is then generated that projects the efficiency of the design as well as a comprehensive checklist of guidelines the designer has followed.
Modern LEDs have given way to effective control of lighting systems. For instance, a high-bay application that has HID fixtures can achieve similar results with LED fixtures, minus the abnormal losses. Instead of operating these fixtures continuously, occupancy sensors can be used to dim the LEDs or turn them off completely, since they don’t have cool down/warm up requirements like that of HIDs.
Furthermore, if the owner requires an advanced lighting control system that packs remote control, then engineers can be instructed to follow a lockout-tagout style procedure that prevents certain loads from turning on until the maintenance is complete.
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