What is the most cost effective and energy efficient design solution?

Several factors should be considered when evaluating the cost effectiveness and energy efficiency of a proposed lighting design:

  • Access to daylight: The cost and energy efficiency of your lighting system will depend on natural light availability. Whenever possible, a lighting designer should examine how best to leverage daylight, as this will allow you to avoid switching on artificial lighting.

  • Technology: Lighting technology has developed quickly in recent years, with lamps providing great improvements in lighting efficiency. Traditional incandescent bulbs are being fast replaced by a new generation of lighting such as compact fluorescent lamps (CFLs) and light-emitting diodes (LEDs). LED lighting, with lamp lifespans exceeding 50,000 hours of operation and with a possible output of 200 lumens per watt (power), stands out as the most cost and energy efficient technology for many uses. Considering the light output (lumens), the power (watts) used, or total cost of ownership, they consume approximately 80% less energy than halogen lamps and 60 to 70% less than traditional fluorescent lamps. Some LEDs offer additional functionality, for example embedded sensors allowing the user to monitor energy use or the operation and maintenance of lighting fixtures, as well as the potential for wireless data communication over the visible light spectrum (LiFi).

  • Lighting Control: Lighting efficiency will depend on the compatibility of your new lamps with the lighting control system, e.g. timers, motion detectors and dimmers. Without suitable lighting control, even the newest generation of lighting will incur unnecessary energy costs. Conversely, teaming a control system with compatible efficient light sources can yield significant savings. Digital lighting control systems allow energy managers to better understand how lighting is used in a building, improve system design and optimise energy efficiency.

    When choosing the most appropriate control method, it is important to take into account:
    • Type of space, ranging from ‘owned’ (e.g. a small consulting room) through ‘shared’ (e.g. an open-plan office) to ‘managed’ (e.g. a restaurant) spaces
    • Occupancy level and how the space is used
    • Amount of daylight available, considering such influences on lighting as skylights, daylight harvesting, type of window glass, wall colour etc.
    Modern, automatic lighting control systems use smart technologies to optimise lighting. They are based on the following three functions:
    • Presence control: acoustic or movement detector
    • Time control: time switch or programmed control
    • Daylight linked: simple photocell or photocell plus regulator
    Commissioning of the lighting control system is particularly important during both the installation stage and subsequently during normal operations. This quality assurance process identifies lighting requirements at the outset and ensures that, once installed, lighting systems perform according to the design intent.

    If the control system does not perform as designed, energy savings may not be realised. This includes too-stringent controls; a system that is too aggressive in switching on/off and dimming can result in occupant complaints, reduced lamp life, and may lead to automatic controls being manually over-ridden.

    The CIBSE Commissioning Code L: Lighting presents standards of good practice in this area. The Code provides guidance on how to set up a commissioning plan for a project, to manage the process of ensuring that the design intent is realised and that the users of the lighting installation are aware of the operation and benefits of the lighting installation, as apply to their particular use of the building.

The following figure summarises the main characteristics of example relatively-efficient light sources:

For example:

Lamp Type
Efficiency (lumen/Watt)
Lamp Life (hours)
Colour Rendering Index
Installation Cost
Operational Cost
Induction Lamp
60 - 80
60,000 - 100,000
Metal Halide
50 - 100
6000 - 12,000
High Pressure Sodium
80 - 100
12,000 - 16,000
20 - 200
20,000 - 100,000

Further reading: