After HVAC system, lighting system is the next largest energy consumption system in any commercial building. Usually lighting consumption is expressed in the form of lighting power density.

The lighting power density (LPD) can be defined as the lighting load in watts/sq ft (or watts/square meter).

Particularly, for a commercial building it is much more important to implement a good quality lighting system to avoid problems like glare and dimming as well.

All the green building rating system across the world put special emphasis on Day lighting. In LEED lighting credit, in some cases it is important to achieve 50-70% daylight. As The lighting loads has a concern with the availability of daylight. Hence your occupied areas requires a combination of artificial lighting as well as sufficient day lighting.

The use of daylight is analysed by various softwares are available or floor plate analyses can also be conducted.

ASHRAE 90.1 offers two methodologies to calculating LPD –

• The Building Area Method and
• The Space-by-Space Method.

The Building Area Method lists approximately 30 different building types (Office, School, Hospital, etc.) and provides an LPD for the entire square footage of the building

The Space-by-Space Method considers each room individually. The Space-by-Space method lists approximately 100 space types (Open office, Enclosed office, Classroom, Restroom, Corridor, etc.) and provides an LPD for each space of that type in a building. This is a much more difficult.

In order to achieve a good LPD it is important not only to select energy efficient lighting fixtures but also use of good lighting control, dimming switches and sensors etc. are also needed.

Lighting effects not only reduces the direct energy consumption of the building but also reduces load on building’s HVAC system.

Following is the example of daylight analyses of a building that has been registered to LEED certification.

We have performed daylight analysis of a commercial building. Having G+13 floors. The model that has been made in design builder is shown below

As per LEED EQ credit Requirement – Daylight simulations has performed with clear sky conditions at 9:00 a.m. and 3:00 p.m. within 15 days of each equinox.

Percentage of regularly occupied area that is daylighted (in %) must be atleat 75% for 1 point and 90% for 2 points.

Design Builder version 4.0 have been used to model and simulate the building for daylighting Analysis.

Technical Specification of Glass used

Visible Light Transmittance – 25%

Over Heat Transfer Coefficient – 0.86 (U –Value in BTU/ hr ft2 °F)

Shading Coefficient – 0.39

Solar Heat Gain Coefficient – 0.34

The analyses of each floor has been done individually and the pictorial view result outcome is shown only of G.F in the picture below

From the complete analyses and calculations prescribed in LEED, it has been concluded that 80% of the total occupied area is daylighted. Hence, meets the LEED requirements for achieving 1 point under EQ credit.

There are many other advantages of adopting energy efficient lighting system such as-

• Energy efficient bulbs use about 25-80% less energy than traditional bulbs, which means you will save a significant amount of energy.
• Energy efficient bulbs last much longer than traditional lights. This means even though being costlier than traditional bulbs, we need not have to replace them as often, so we are actually saving money down the road.
• These emits low heat thus reducing buildings HVAC system load.