Building design is arguably the most important these days. And the energy efficiency of a building is one of the most significant things. The designers of architecture, engineers, and lighting designers have to ensure a balance of functionality, comfort, and sustainability. Lighting power density (LPD) is one of these important concepts that has been employed in such a balance.

LPD is also applicable in construction codes, energy regulations, and green certification. Unless you are a newbie who has never glanced at the architectural plans of energy-efficient buildings, you must have heard this term. But what is it after all, and why should it be so important? OK, let’s take it slowly.

Lighting Power Density Definition

Lighting Power Density (LPD) is what is known as the electrical power consumed by the lighting system. Within a building area, divided by the area of the building.

It is stated as watts per square meter (W/m 2 ) or watts per square foot (W/ft 2 ).

Formula:​

              LPD=Total Lighting Wattage Installed​ / Area of the Space 

For example, if a 100 m² office has lighting that consumes 500 watts, its LPD is:

                              LPD=   500/100   ​=5 W/m²

Lighting efficiency between rooms, buildings, or designs can be compared using this simple calculation.

What of the Importance of LPD?

The lighting takes a sizable part of the electricity use in buildings. Large LPD translates to greater energy consumption, and smaller LPD translates to efficiency.

Energy efficiency requirements 

• The building codes sometimes post the largest LPD values. Manufacturers have to remain within these tolerances.
• Savings on costs -Lower LPD lowers electricity bills.
• Environmental impact- the use of energy-efficient lighting reduces the emission of gases.
• Energy performance benchmarking – Can allow a comparison of energy use in buildings.
• It has never been easier to maintain the LPD low with such modern solutions as LED outdoor lighting.

Influences on LPD

The lighting power density of a building is dependent upon several things:

1. Light source type used :

LEDs use less energy compared to fluorescent or halogen lamp light sources.

2. Fixture efficiency:

Properly designed fixtures radiate light further, and the ability to get away with fewer watts.

3. Room use:

The offices or classrooms need more light than the storage rooms.

4. Lighting plan/ arrangement:

Nicely arranged lights do not waste light and decrease LPD.

5. Controls and sensors:

Dimmers, timers, and occupancy sensors limit the use of unnecessary lights.

Standard LPDs, Typical LPD Standards

Buildings of different types have various limits of LPD, typically in the form of codes such as ASHRAE or IECC. Below are typical examples (rough estimates, which may differ by region):

• Offices: 8-10 W/m²
• Classrooms: 911 W/m²
• Hospitals: 12-14 W/m²
• Retail Store: 12-16 W/m²

These values will assure the best lighting of spaces without wastage of power.

Ways of Achieving the LPD Targets

To maintain the power density of lighting within recommended levels. Several strategies are available to the designers:

• Go LED- LED lighting with outdoor lamps and indoor LEDs cuts way down on watts.
• Design efficient fixtures – select the light fixtures that have controlled light output.
• Use daylight combination, integrate natural light with others.
• Put in smart controls. Installation of motion sensors and dimmers minimizes the use of unnecessary functions.
• On correct spacing, the zones of light do not overlap.

The Advantages of Low LPD

1. Better sustainability rating (LEED, BREEAM, etc.)
2. Extended length of fixture service life, particularly LEDs
3. Less heat in the lights can cause reduced load on air-conditioning.
4. More adherence to national energy codes

LP density and Building Regulations

Energy Codes in every corner of the world demand that they follow the greatest amounts of LPD. Countries have their codes, but they all roughly work by the same principles.

For example:

• The most limiting LPD are established in ASHRAE 90.1 (USA). This gives strict limits, based on the type of building.
• European standards (EN 12464-1). These are aimed at having a balance between energy consumption and visual comfort.
• In the Middle East and Asia, LPD is also employed in local codes in Asia and the Middle East. Its main purpose is to prompt efficient lighting design.

The lighting power density guide can ensure designers design to specifications. And achieving a proper lighting power density would prevent penalties.

Illustration: LPD Outdoor Lighting

Although the use of LPD is regularly talked about in indoor spaces, it applies to outdoor projects as well. The parking spaces, walkways, and exteriors of a building also need efficient lighting.

In these instances, LPD is significantly reduced by using LED outdoor lighting, as the LEDs provide high luminosity using very little wattage. That is why cities and corporations around the world are changing their street, landscape lighting, and security lights to LED.

Conclusion

Lighting Power Density (LPD) is straightforward. Yet an exceedingly effective tool in energy-efficient building design. It informs us about the amount of power utilized in the lighting of a unit area. It is useful in controlling the amount of energy consumed in homes. Offices, hospitals, and outdoor areas.

Adhering to an effective lighting power density guideline and applying the energy-saving options plans. Such as LED outdoor lighting, such organizations can save money, fulfill regulatory requirements, and become ecologically responsible.

The ability to have efficient lighting is no longer optional, but rather the basis of responsible design in the contemporary world.