Fonte (Source): Consulting-Specifying Engineer
Por (By): Michael J. Mar, PE, LEED AP; and Robbie Chung, PE, LEED AP; ESD
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Clients are asking lighting designers to help them save on energy costs, and replacing fluorescent, HID, or other lights with LEDs is in high demand. Here’s a look at the codes and guidelines that define LED use, including ASHRAE Standard 90.1, California Title 24, Dept. of Energy, and IECC.
- Recognize the impact of various lighting sources on the energy efficiency of a building.
- Know the codes and standards that dictate lighting design.
- Understand the availability of rebates and incentives that may exist for utilization of LEDs.
According to the U.S. Dept. of Energy (DOE), LED lighting can have the greatest potential impact on energy savings in the United States. The DOE estimates that widespread use of LEDs could save the equivalent of the annual electrical output of 44 large, 100-MW electric power plants for a total savings of more than $30 billion at today’s electric rates.
This solid-state lighting technology that uses a semiconductor to convert electricity into light is one of the most energy-efficient and durable lighting technologies today. In fact, LED light sources can be six to seven times more energy efficient than conventional incandescent lights, allowing for significant reductions in energy use. Quality LED light sources can have a service life of more than 50,000 hours, or more than 50 times longer than incandescent lamps and four times longer than compact fluorescent lamps. That is a life of more than 5 years if run 24/7. LEDs are robust, resistant to breakage because of their compact size, and easy to maintain.
Other benefits to LED lighting include:
- Emittance of light of an intended color without using any color filters
- Emittance of light in a specific direction, reducing the need for reflectors and diffusers that can trap light
- Negligible on/off time-full brightness can be achieved in less than a microsecond
- Ideal for uses subject to frequent on/off cycling, unlike incandescent and fluorescent lamps that fail more quickly when cycled often
- Difficult to damage with external shock due to its solid-state components
- Minimal heat radiation, i.e., reduced cooling requirements
- Inherently dimmable
- Comes in a wide variety of styles, colors, and sizes to fit any décor and task
- Availability of retrofit components for numerous luminaire types (retrofit kits shall be UL listed).
With these significant advantages, LED can be a great solution for certain retrofit and renovation applications.
Evolution of LEDs
Even though LEDs currently have many advantages, it took years to optimize this technology and increase its efficacy to today’s average 70 to 100 lumens/W. With extremely high costs, the first use of the visible-spectrum LED more than 50 years ago was limited to applications such as replacement of indicator lamps in displays and appliances. It wasn’t until 2000 that the DOE began funding solid-state lighting research and development, allowing LED technology to develop rapidly with improvements in the use of materials, extraction of more light, and other underlying technical challenges that previously hindered its widespread use as a source for general illumination.
During the LED research and development phase, each manufacturer published lamp life and efficacy values based on its own criteria, resulting in inconsistent performance levels. However, standards were recently developed to allow for accurate comparisons between different manufacturers’ LED luminaires and between LEDs and other lamp types. Some of the critical LED standards established include Illuminating Engineering Society (IES) LM (lighting measurements)-79 and LM-80 standards. LM-79 is a standard method for photometric lighting measurements. LM-80 is a standard method for measuring lumen maintenance, which is used to make useful lamp life projections. Cost analysis and light level calculations are now able to be completed more accurately and consistently, and therefore LED luminaires specified on projects should be compliant with these standards.
As LEDs continued to advance technologically, energy codes were simultaneously revised. In fact, these revisions helped push the implementation of LED sources. For example, when energy codes changed the requirements to a maximum of 5 W/side on exit signs, LEDs become the norm because the incandescent and compact fluorescent types could not comply.
Each new edition of the energy codes establishes more stringent requirements, with California Title 24 energy code leading the way. Title 24 has modified the requirements necessary to comply with the latest lighting power density and controls requirements for replacement projects, which makes LEDs an appealing solution because other lamp technologies cannot easily meet some of these requirements.
The latest 2013 California Title 24 standards, which took effect on July 1, 2014, expanded requirements for photo and occupancy sensors and multilevel lighting controls, both indoors and out, making adaptive lighting the new standard in California. The newest standard also requires many more retrofit and renovation projects to meet new construction standards for lighting than in the 2008 standard. Spaces in which less than 10% of the lighting is being changed out, or buildings in which fewer than 40 ballasts are being replaced are exempt. Otherwise, all new lighting in an existing building must meet not only the lighting power density (LPD) requirements, but also most of the controls requirements (including dimming). In addition, lighting in exterior spaces, such as parking garages, lots, and loading areas, will be required to have occupancy controls with at least one step of 20% to 50% of full lighting power. The wide range of retrofit LED products available today allows for a more economical solution to meet codes without having to replace the entire luminaire.
Other states have adopted various versions of the International Energy Conservation Code (IECC) or ASHRAE 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings. The major changes in lighting for ASHRAE 90.1-2013 include adjusted LPD, more stringent lighting control requirements, and a new table format for determining lighting power and control requirements in individual spaces. Most interior LPD values were lowered. For example, building area method LPDs were adjusted for retail spaces to 1.26 W/sq ft (down from 1.4 W/sq ft), offices to 0.82 W/sq ft (down from 0.9 W/sq ft), and hospitals to 1.05 W/sq ft (down from 1.21 W/sq ft). The other significant changes from the 2010 standard are a new table format for determining LPD allowances using the space-by-space method and minimum mandatory control requirements using either the space-by-space method or building area method.
Similarly, the 2015 version of the IECC has made modifications from the previous released code to include reductions in LPD values and enhanced lighting control requirements. The 2015 IECC continues recognition of the space-by-space method that was re-introduced in the 2012 version as a compliance path along with the building area method, which provides additional flexibility. The IECC space-by-space method is based on ASHRAE 90.1, with subtle differences in space types and lighting power allowances. In the end, the continual trend for reduction in installed lighting power densities makes fixtures with high efficacies, such as LEDs, a viable option, especially for U.S. Green Building CouncilLEED projects where the goal is an even greater energy reduction below code.