Lighting and the energy codes

Engineers have many resources when designing energy-efficient lighting in nonresidential buildings. Lighting designers do not have to sacrifice quality or reduce lighting levels just to meet energy codes.

10/26/2015


This article is peer-reviewed.Learning Objectives:

  • List the codes and standards that outline energy-efficient lighting design, such as ASHRAE Standard 90.1 and the International Energy Conservation Code.
  • Apply lighting power density to lighting design.
  • Recall that lighting design software and lighting controls play a role in lighting design. 

Prior to the 1973 gasoline crisis in the United States, energy conservation codes didn't exist. Today, the energy laws have virtually stopped the sale of incandescent bulbs that Thomas Edison worked so hard to develop. Offices that were routinely illuminated to 200 footcandles (fc) are now illuminated to 30 fc with task lighting to make up the difference (in accordance with the Illuminating Engineering Society, IES).

Architects, developers, and owners constantly complain that there is not enough light, whether they are talking about offices, common areas, corridors, or parking lots. Historically, offices that may have used 5 W/sq ft to 8 W/sq ft for lighting, now are allocated 1 W/sq ft. Exterior lighting is greatly restricted and dark-sky initiatives, such as the International Dark Sky Association, are normally required by most authorities having jurisdiction (AHJ); general exterior lighting on building facades is no longer permitted because it wipes out the visibility of stars in the vicinity of urban areas.

For most states and jurisdictions, interior and exterior lighting design for new or renovated facilities is controlled by either ASHRAE 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings (2013 edition) or the International Energy Conservation Code (IECC, 2012 edition), depending on which code is adopted by the AHJ. These codes have similar restrictions concerning maximum lighting power densities (LPD) for various facilities, but they approach the final calculations in different manners.

ASHRAE gives you a list of various types of facilities and then has subcategories within each facility type with specific restrictions on the LPD for each of the space categories. For instance, a hospital is divided into 14 different space types from corridors less than 8 ft wide to recovery areas to nurse stations. The total area of the facility must then be divided into each of these categories with specific areas for each space. The calculation then multiplies each space category by its allowable LPD to come up with a total allowable lighting power permitted for the hospital. The wattages for every lighting fixture in each of the space categories is then totaled and the fixture wattage total is compared to the maximum lighting power permitted. If the total lighting fixture wattage is less than the maximum permitted wattage, then the facility passes, but if the wattage is greater, then the facility fails. Most jurisdictions will not issue an occupancy permit to a facility that fails this calculation.

For IECC's 2009 edition—still in use in many jurisdictions—there are a number of facility types, but the total building area is used for the total lighting power. Using the hospital example, the entire building must have an LPD of less than 1.05 W/sq ft. Calculate the total hospital area and multiply it by 1.2, which results in a total lighting power for the facility. By totaling the Watts used by every light fixture in the facility and comparing it with the calculated lighting power above, the facility passes if its total lighting power is less than the permitted lighting power.

In the 2012 edition, the IECC modified its approach to more closely match the ASHRAE methodology, which allows space-by-space lighting power calculations as well as the previously described "building area method" used in the 2012 IECC.

Other lighting codes

In addition to our concentration on ASHRAE 90.1 and IECC, there are a number of federal acts and organizations that have regulations and opinions that affect lighting. These include:

Design lighting issues

As the engineer proceeds with his lighting design, applying all of the applicable codes and standards, he also must research the best way to apply the lighting fixtures that are desired by the owner and architect. He may find that the desired fixtures will not meet these codes, no matter what lighting source used in the fixtures. There are LED fixtures that now achieve more than 102 lumens/W, but T-5 fluorescent lamps manufactured by a well-known lamp manufacturer can achieve more than 105 lumens/W. Other LED fixtures still are in the 60 to 70 lumens/W range and there will be significant lighting loss by using these less-efficient fixtures.

Also, the lighting engineer should take the lamp lumen depreciation (LLD) of the selected lighting source. With an LLD of 0.91 to 0.95 for fluorescent lamps, according to data from a large fluorescent lamp manufacturer, and 0.70 for LEDs, there will be significant lighting loss due to lumen depreciation. On the positive side, the LLD is applied over 50,000 to 60,000 hr of operation for LEDs and 35,000 to 60,000 hr for selected T5 fluorescents. By carefully selecting the fluorescent lamp, relamping of fluorescent fixtures may be on the same interval as replacement of the diode elements and drivers of the LED fixtures at a significant cost savings.


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Douglas , TX, United States, 11/18/15 11:42 AM:

Regarding the comments in Design Lighting Issues, make sure you are evaluating fixture delivered lumens between both LED and fluorescent. While a T5 may have an efficacy of 105 LPW, an 80% fixture efficiency will drop the delivered lumens down to 84 LPW. Most LED specifications are reporting delivered lumens which often exceed 100 LPW now.

Also, a blanket statement of 0.7 LLD for LED's is somewhat old school. Most major manufacturers are publishing the LLD at 50k, 60k or even 100k hours. These are based on TM-21 test standards and are often as high as 0.90 LLD at 100k hours.
Anonymous , 11/19/15 12:10 PM:

I appreciate this kind of info being routinely posted. It keeps me up on things being semiretired, but being called on periodically by allies in the industry for help.
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