A few years ago the Governments motto was education, education, education. More recently it seams to be environment, environment, environment. Even ignoring the government spin, there is still good reason to make lighting installations as energy efficient as possible, for a start it can save you money, and secondly it could save you from having to swim to work rather than catch the bus.

There is no doubt that recent advances in technology have made lighting much more efficient a typical office luminaire is up to 4 times as efficient as one from the 1960’s (if the motor industry had the same attitude to energy saving a family salon car would be able to do over 100 mpg by now) but energy is still being wasted by not using the most efficient lamp/gear/optical combinations, by not controlling light properly, and by not considering where light is actually needed.

With the use of well designed lighting it is possible to light an open plan office to a uniform level of 500 lux for less than 12w/m2 which is at least 30% less than was achievable as little as 10 years ago. However with introduction of LG7 and EN12464 which encourages us to consider the task and not blanket light the whole area this can be reduced further. Based on an occupancy density of one work station per 5 sq.m. using a combination of ambient lighting and task lighting it is possible to get down to nearer 8 w/m2 and still give 500 lux or more on the task area. Further savings are possible because people will turn their task lights off when the leave the desk. This is based on Luxo’s new “Ninety” LED task light which will give up to 1000 lux on the task whilst consuming only 6 watts of power, with a lamp life of 45,000 hours. This represents a major step forward in energy efficient and mercury free lighting, making LED’s viable in the office environment.

Task lights have the added advantage because with adjustment the can provide up to 1000 lux on the task without disturbing fellow staff, as recommended by the CIBSE Fact File No. 10 when considering the aging work force.

The following is a brief discussion of the 5 major factors influencing the overall energy efficiency of a lighting installation:

Lamp Efficiency
The most efficient of the new generation of T5 lamps is the 35W HE (high efficiency) which gives 94 lm/W, however the 24W T5 HO (high output) gives just 73 lm/W, a difference of 30%. Generally speaking the lower the lamp wattage, the less efficient the system, so try and use the higher wattage T5 HE lamps. Also the more lamps you use the more mercury waste you are storing up for the future, so again use longer more efficient lamps where possible. Rather than use say a 4x14W 600 square module, if possible use a 2x28W pendant or better still use even less 2x35W pendants.

Control Gear Efficiency
One problem with lighting installations is that developers look at the initial cost of a lighting system rather than the whole of life cost. Low cost electronic ballasts, as well as being less efficient, do not have a warm start facility thus reducing lamp life. This reduction in lamp life can be dramatic if PIR’s are used or the lamp is switched more than 3 times a day, so any energy saving is far outweighed by lamp costs, which in turn impacts more on the environment due to the hazardous waste created. So always specify warm start control gear, and check the power factor.

Luminaire Efficiency.
Probably the biggest single factor in the overall efficiency of a lighting scheme, is the efficiency of the luminiare in terms of light output ratio (LOR) and the distribution of the light. The latest building regulations Part L, give a requirement of 45 luminaire lumens per circuit watt. In other words if a lamp has an efficiency of 90 lm/W then the luminaire only need be 50% efficient. With T5 lamps which reach their peak output at a higher temperature than older lamps it is possible to reach LOR’s of over 80% so we should not be content with just achieving Part L requirements.

The Government Enhance Capital Allowance Scheme (ECA Scheme) is much stricter on its requirements because it specifies the amount of light delivered to the working plane, and has higher values than part L.

Designing to Part L or the Government ECA guidelines is all well and good, but you can comply to these criteria quite easily and yet still be wasting a vast amount of energy. How? By lighting parts of a building that are rarely used or unoccupied, by lighting to incorrect levels, or by lighting areas that are already well lit with natural daylight. This leads us on to the following two points:

Use of Controls
For relatively low cost, controllable ballast can be built into a luminaire allowing it to be dimmed or switched by control sensors. These can detect daylight and dim the lighting accordingly or switch the lighting off when the area is unoccupied. Even in an existing building and using existing wiring controls can still be used because sensors can be built into each luminaire so the individual fitting becomes “intelligent” and will dim and switch itself depending on ambient conditions. The use of such controls and areas with natural light can cut energy use by 40% or more.

Best Use of Light
If light were, water or something we could see we would take much more care of how it is used and would be more careful with it. If we are watering the garden for example we would not water the drive way and patio as well as the plants and lawn (that is if you are allowed to use a hose at all). I hope I’m not being too patronising here but you get the idea. Likewise, as mentioned in the opening paragraphs, with lighting we do not have to light all parts of an area evenly. With well designed ambient and task lighting we can save energy and cater for a wide variety of worker requirements.

Hopefully this gives a common sense guide on how to achieve an energy efficient lighting scheme which will not only help reduce carbon emissions, but also save money.

Steve Willis, Technical Manager, Luxo

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