LENI: The Lighting Energy Numeric Indicator

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Did you know that buildings account for 40% of all electricity use in the US?

If you’ve been part of efficiency discussions in the construction industry, you’re most likely aware that lighting is responsible for a large portion of all electricity used in buildings – both commercial and residential.

Therefore, it’s fair to say that lighting efficiency in buildings is a topic that needs to be constantly addressed and discussed.

Government and state laws continue to effectively push engineers to minimize energy use by implementing regulations and standards such as Title 24. At Hyperikon, we praise these initiatives. But as we continue to push for more efficient lights, we can’t help but to critique ourselves and attempt to find new ways to increase efficiency.

One method that we feel haven’t been discussed enough is LENI (lighting energy numeric indicator), a European measure used to determine lighting efficiency in buildings. In this article, we discuss how LENI works, how it pushes us to reach zero ground energy and whether its methodology could be applied to buildings here in the U.S.


What is LENI?

LENI, or Lighting Energy Numeric Indicator, is a measure of the efficiency of lighting within a building space. It is calculated as the number of kilowatts per hour per square meter of space that a lighting system uses, taking into account all of the lighting fixtures present and any controls on their energy use.

LENI builds on the traditional method of calculating lighting efficiency per fixture, known as the Luminaire Efficacy Method (LEM). While LEM looks at each individual lighting unit (regulating their minimum lumens per watt), LENI is an indicator that considers a complete lighting installation.

Furthermore, LEM ensures efficiency for individual lighting units – making it the perfect measure when shopping for single luminaires. But it ignores the fact that most buildings use multiple lights in a coordinated system to adequately light an entire space. It also disregards lighting controls such as occupancy- or daylight-based dimmers and timers. These are routinely used in modern lighting systems both to increase net energy efficiency and to increase end-users’ satisfaction with how a building is lit.

Why is LENI Important?

By taking into account the energy used for lights over an entire space, LENI accounts for the extra efficiency introduced by lighting controls and system design.

The efficiency of individual bulbs, and especially LED lights, has dramatically increased in recent years. But that is only half the equation for lighting efficiency—the other half is to position those light fixtures in ways that maximize the utility of output lumens and to add controls that minimize wasted lumens.

Ultimately, LENI will allow for greater gains in lighting efficiency and greater reduction in energy consumption for buildings.

This is especially important looking towards the future. Although the trend of increasing efficiency for LEDs is likely to continue, there may ultimately come a point at which engineering ever more efficient lights brings diminishing returns. At that time, adjusting lighting controls and system designs - which LENI accounts for - will be the primary path forward for increasing lighting efficiency.

For now, basing energy efficiency regulations on LENI gives building planners more flexibility in designing how a space is lit. Efficiency targets based on LENI require designs that are tailored to an individual building or space and encourage the implementation of energy-efficient lighting controls.

How is LENI Calculated?

There are several different methods for calculating LENI based on how exact the metric needs to be for regulatory purposes. Here, we’ll walk through a simplified calculation that is outlined in the UK’s 2013  Non-domestic Building Services Compliance Guide. Keep in mind that LENI is typically calculated on a per-room basis rather than on a per-building basis to make the metric as accurate as possible.

First, some important terms that you need to know in order to calculate LENI:

  • The luminaire power is the total power, in watts, of all fixtures installed in a lighting system.
  • The constant illuminance factor is a multiplier determined by the presence of lighting controls like dimmers. When there are no dimmers or other controls in use, this factor is set to a value of 1.
  • The occupancy factor is another multiplier to account for lighting controls. In this case, when there are no controls to dim or turn off lights when a space is empty, the occupancy factor is set to a value of 1.
  • The daylight dependence factor accounts for lighting controls, such as dimmers, that are sensitive to external lighting conditions. When there are no daylight-based lighting controls, this factor is set to a value of 1.

  • To calculate LENI, start by determining the total energy used by the lighting system within a space each year. This can be broken down into daytime energy use and nighttime energy use, accounting for any lighting controls that may be present through the constant illuminance, occupancy, and daylight dependency factors.

    Second, add the parasitic energy consumption. This is the energy used by lighting controls themselves. If there is a standby or emergency lighting system, such as in many commercial buildings, the energy required to charge this system should also be included in the parasitic energy consumption.

    Finally, calculate the square footage of the space being lit. Add the lighting energy use and the parasitic energy use to get the total energy used per year after accounting for all lighting components and controls. LENI is equal to this total energy demand divided by the square footage.

    Where is LENI being used?

    LENI has been adopted as the primary metric for lighting efficiency in new buildings in Europe. In the European Union the use of LENI is outlined in  EN 15193, the Energy Performance of Buildings Directive, which was released in 2006. The UK adopted LENI benchmarks as requirements for new residential and commercial buildings in 2014, as part of a revision to Part L of the country’s Building Regulations code.

    LENI does in many cases make it more difficult to determine whether a lighting system complies with regulations. However, adding LENI benchmarks into regulations also helps push building planners towards using more efficient lighting systems, which will likely decrease European countries’ energy consumption and carbon emissions in the long run.

    Energy Efficiency and the Future of LENI in the US

    If you haven’t heard of LENI until now, that’s probably because this metric of efficiency isn’t yet being used for building construction in the US. The closest comparable regulation to what Europe is doing is California’s Title 24, which mandates some of the strictest lighting efficiency standards in the states. Title 24 leans heavily on lighting controls like countdown and occupancy timers, as well as prescribes a maximum wattage per square foot allowed in certain building spaces.

    So far, Title 24 has managed to improve energy efficiency, but the code may fall short of what LENI has done for building construction in Europe. Under Title 24, most building designers can meet the efficiency requirements simply by adding lighting controls and switching to low-wattage LED bulbs.

    While these are unquestionably great initiatives, one may argue that these regulations do not inspire a major push for an adaptive approach to lighting design. That push has been left to individual experts, who use their own methods of calculating lighting efficiency in buildings – often by using photometric data and precise lighting layouts.

    While LENI has not been explicitly proposed by a regulatory agency in the US, changes to lighting design standards may be coming. Title 24 is revised every three years, and California is considering requiring that all newly constructed commercial buildings are zero net energy as soon as 2030. Residential buildings could be required to transition to zero net energy even sooner.

    Such a shift could force the adoption of LENI or a similar high efficiency approach to lighting design in the state and set a new standard for lighting systems across the country. After all, even with increasingly efficient LEDs and solar panels, building designers are going to need every tool in the toolbox to push net building electricity consumption to zero.

    As is often the case, if such an indicator were to be introduced in California, look for dominoes to fall around the rest of the country. Washington and Oregon tend to follow closely behind California when it comes to efficiency standards, while states like Arizona and Texas that enjoy strong solar energy production could use a more efficient paradigm for lighting design in order to make the jump to net zero energy buildings.


    The US may be on the verge of transitioning to outcome-based regulations for lighting efficiency thanks to the growing push towards low- and zero-energy buildings. When that happens, the country could see widespread adoption of a metric like LENI, further revisions to Title 24, or the development of another efficiency indicator altogether.

    What do you think the future of lighting efficiency in the US will look like? Does it involve LENI? Leave us a comment below to let us know whether you think LENI could be adopted in the US and whether you see any direct use for it.

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