Quick wins: Let there be light

13th October 2011


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The first in a new series looking at ways to reduce resource use focuses on lighting controls

The Carbon Trust estimates that lighting accounts, on average, for 25% of an organisation’s electricity costs. Simple steps can be taken to reduce this. Switching off lights in empty rooms and making the most of natural light are just two no-cost options. Spend a little money and even greater savings – both financial and in terms of emissions – are possible.

Commercial lighting consumes 42TWh of electricity in the UK each year, resulting in 22 million tonnes of carbon emissions. Lighting controls can reduce lighting energy consumption by 30–40%. Switching off lighting in rarely used areas such as storerooms can achieve savings in such areas of up to 90%.

Estimates by the trust suggest that payback from installing lighting controls is typically five years or less, although some lighting companies claim payback can be achieved in 18 months. The trust also says that occupancy sensors, for example, provide improved convenience, a better working environment and increased security.

Controls and where to use them

There are three basic types of lighting controls, each more suitable in specific spaces/locations than others, but they can also be used in combination:

  • Occupancy sensors – as the name suggests, occupancy sensors detect presence, switching lighting on and off when an area is occupied or unoccupied. There are three main types of occupancy sensor: a passive infrared (PIR) sensor, with lighting triggered by warm objects, such as the heat emitted by a person; an ultrasonic sensor (US), which sends a high-frequency sound wave – undetectable to the human ear – into areas, with lighting triggered by the movement of solid objects; and a microwave sensor (MS), which works on a similar principle to the US, but uses much higher frequencies. Although they are less common, US/MS sensors are preferable in some areas, as furniture and machinery can obscure PIR sensors, which are restricted to detecting motion in “the line of sight” of the sensor.
  • Daylight (or photocell) sensors – monitor natural light, switching off or dimming artificial lighting in response to changes in available daylight. Lights tend to be switched off or dimmed in groups (zoning), with those nearest windows, for example, separate from the rest. Daylight sensors should be used with timing controls or occupancy sensors to allow lights to be switched off when areas are unoccupied. The Carbon Trust advises that dimming generally saves more energy and, compared with switching, is less obtrusive to the occupants. It also says the cost of installing daylight sensors can be recovered in less than one year.
  • Timers – can be set to switch lights on and off at predetermined times where workplace hours are fixed. Time-delay switches, which turn on lighting for a short period, can be effective in areas that are normally unoccupied, such as aisles and storerooms.

Lighting controls can be integrated into fittings but this would only normally be considered if the lighting needs to be renewed. Building control systems are also available but are more suited to new builds or major building refurbishments rather than to retrofitting existing lighting systems.

Most controls can be set to operate automatically or semi-automatically. Automatic means the control turns the lighting both on and off, while a semi-automatic setting switches lights off when they are not required, but they must be switched on manually. Semi-automatic controls generally deliver greater savings.

Costs and savings

The Carbon Trust says that organisations should consider installing lighting controls where there is the potential to save at least 500kWh of electricity a year. This could be achieved, for example, with a 500W lighting load, being turned off for 1,000 hours per year – approximately four hours a day.

The cost of installing a lighting control will vary from contractor to contractor and installation to installation depending on a number of factors, such as accessibility to existing wiring and height of the ceiling. The trade price of a PIR occupancy switch is about £40 and its straightforward installation is about the same again.

The Carbon Trust’s 2008 guide to lighting equipment eligible for enhanced capital allowances (ECA) provides some indication of the level of savings that can arise – although energy costs are now much higher.

The guide provides the following example: A 400m2 warehouse with a fluorescent lighting installation that is left on for 10 hours a day, five days a week, even though the average rack is only visited one-quarter of that time. Installing ECA-eligible occupancy detectors (see below) on each of the 10 racks is predicted to save 70% on lighting-energy use in that part of the warehouse. In this scenario, annual financial savings are estimated at £664, while energy savings amount to 8,736kWh and carbon emissions are down 3.8 tonnes. The cost of 10 sensors and their installation was put at £900.

The trust says that savings from installing lighting controls are roughly proportional to floor area, so a larger warehouse would achieve higher savings. It also notes that combining occupancy and daylight sensors can provide even bigger savings.

A UK company that designs and manufactures controls for lighting, heating, ventilation and air conditioning systems says that one of its PIR occupancy switches installed in a single office can typically save four hours of lighting a day, with an annual saving of £32 on electricity bills, while a PIR occupancy switch in a distribution centre warehouse typically saves 20 hours a day and £263 on the annual electricity bill.

Lighting controls such as occupancy sensors and daylight detectors come under the government’s ECA scheme (the latest list of energy-saving plant and machinery – the Energy Technologies List – that qualifies for ECA. The allowances enable businesses to claim 100% first-year capital allowances on spending on qualifying plant and machinery. Qualifying expenditure can include not only the actual costs of buying the equipment but also other direct costs, such as the transport of the equipment to site and some of the direct costs of installation.

Installation and control

An energy survey will identify where potential savings can be made, and modern metering and monitoring solutions provide detailed information on where energy is wasted and therefore where the greatest savings can be made. Most lighting controls can be installed in existing wiring systems, and competent electricians will be able to install simple systems. For larger, more complex installations it is wise to get guidance from lighting control manufacturers.

The main issue with lighting controls is turning lights off or on too soon. Settings are important, and although these will depend on the area covered by the controls, the

Carbon Trust offers the following advice:

  • The delay before fluorescent lights are switched off should be between 10 and 15 minutes – not less than 10 minutes.
  • The switch-off lux level – the measurement unit for light – on internal, switching daylight sensors should be set at three times the required workplace level. So, for example, where the required level is 300–400 lux, the sensing controls should be set to switch off artificial light when levels reach around 1,200 lux. If dimming is used, then the reduction can begin at much lower levels.
  • For occupancy sensors in meeting rooms, store rooms etc, select the “absence” rather than the “presence” control – meaning lights have to be switched on manually when entering, but switch off automatically when there are no occupants. This prevents lights automatically switching on when there is sufficient natural light for the occupants.

Further information:

Lighting will be featured in the Carbon Trust’s “Expert in energy” guidance series in December 2011, and will include a new lighting technology guide and a training webinar. The series has already launched new advice and information on how to: green your business for growth; run refrigeration systems efficiently; implement heat-recovery processes and better understand your organisation’s energy management. Visit the Carbon Trust website to register your place on the lighting webinar and to view the latest content.

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