Down With Lighting

15 June 2006

With energy costs rising and corporates in the spotlight to responsibly reduce their environmental impact, some common sense advice from Steve Willis shows how to achieve more efficient lighting that will not only help reduce carbon emissions but also save on costs

A FEW YEARS AGO THE GOVERNMENT'S 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 to save you money.

There is no doubt that recent advances in technology have made lighting much more efficient, but you do need to be a bit careful and look past some of the advertising slogans. For example, LED's are not very efficient at the moment, some of the new T5 lamps are less efficient than their old T8 counterparts, and not all high frequency electronic ballasts offer the same energy savings. Even the use of controls such as PIR's which you would think to be a certain winner can be counterproductive because of vastly reduced lamp life if not used with the correct lamp control gear.

1. Lamp efficiency
It is not enough just to specify the use of T5 lamps to achieve energy efficiency. For example the most efficient T5 lamp 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 per cent. Generally speaking the lower the lamp wattage, the less efficient the system, so try and use the higher wattage T5 HE lamps. The latest hype is coming from LED producers, but if you read between the lines you will find that unless you are using them for applications where colour is required or for decorative purposes then these are certainly not an energy saving option. A typical output for a white light LED is 25 lm/W, nearly a quarter that of an efficient fluorescent lamp.

However people are taken in by the headlines, I was recently asked by a major retail company to look into lighting their entire supermarket to 1000 lux using just LED's, because they had been told that was the 'future for lighting'.

2. 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 three times a day. Any energy saving is far outweighed by lamp costs, which in turn impacts more on the environment due to the hazardous waste created.

3. 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 per cent efficient. With T5 lamps which reach their peak output at a higher temperature than older lamps it is possible to reach LOR's of well over 80 per cent so we should not be content with just achieving Part L requirements.

The Government's Enhance Capital Allowance Scheme (ECA Scheme) is much stricter on its requirements. For example, it does not specify the efficiency of a luminiare just in terms of LOR but in terms of the amount of light delivered to the working surface. It also takes into account the efficiency of the lamp and control gear.

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:

4. Use of controls
For a relatively low cost, controllable ballast can be built into a luminaire allowing it to be dimmed or switched by manual or automatic controls. 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 'eintelligent' 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 50 per cent or more.

5. Best use of light
If light were water or something we could see in terms of something solid, 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 driveway as well as the plants and lawn (that is if you are allowed to use a hose at all!). Or, if we have a patio with pots then we would not apply an equal amount of water to the whole area, but just water the pots. Likewise with lighting we do not have to light all parts of an area evenly.

As discussed earlier EN12464 and LG7 encourage the targeting of light to where it is needed - on the task. This is where good design using ambient lighting and task lighting comes in. Whereas it was common to light a whole open plan office to say 500 lux, we should now be looking at a much lower general level of illumination. The two documents mentioned above say we can light the general area outside the task area to 300 lux, with 200 lux in circulation areas. The task area can then be boosted to 500 lux with the use of a welldesigned, efficient task lighting. A recent office lighting installation which used these methods estimated that they achieved an energy saving of around 60 per cent, over a conventional scheme, using these methods. An added benefit was, because individuals had control over the lighting on their own work station, and were conscious of energy usage the task lights were only used when the desks were occupied leading to further savings.

... Steve Willis is Technical Manager at Luxo UK Limited