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Lighting system efficiencies for Part L 2010March 2010

The 2010 edition of Part L is going to require even greater efficiencies from lighting systems. Richard Forster identifies the major changes.

You don't have much time. The next edition of Part L is due to be implemented in April 2010. Building designers need to understand the changes very quickly so that projects can comply without the need for last minute revisions.

The 2006 edition suffered from a slow start as the details were not made public until a few weeks before it went live, leaving little time for training and awareness. The success of the 2010 revision will depend on quick uptake if energy consumption is to be reduced significantly.

The 2010 edition of Part L proposes changes that reflect not only technological improvements but also the effects of phasing out tungsten lamps. The extent of the changes will also be influenced by political judgement on how far the public is prepared to make efforts to reduce energy consumption.

There is nothing in Part L that determines the quantity or quality of electric lighting. Ergo, lighting that is not fit-for-purpose could meet the energy criteria and thereby be Part L compliant.

Some designers have continued to justify inefficient light sources on the basis that they provide a better quality of light than is available from low energy lamps. This can be defensible: the cost of occupants can be 15 times that of energy, so efficient visual performance could be more valuable than the fuel consumed.

For domestic buildings the use of low energy lamps is expected to rise dramatically. Low energy lamps installed in light fittings with BC or ES holders will now be accepted whereas before only those fitted in dedicated sockets could be considered.

However, the "reasonable provision" of one low energy lamp in four fittings is to be increased to three out of four. The definition of low energy is also changed to "greater than 45 lamp lumens per circuit watt" from the old value of 40.

For non-dwellings the standards have been raised in three specific ways:

  • general lighting for offices, industrial and storage will be increased from 45 to 55 luminaire lumens per circuit watt
  • general lighting for other areas will rise from 50 to 55 lamp lumens per circuit watt 
  • display lighting will increase from 15 to 22 lamp lumens per circuit watt.

Some commentators have misinterpreted these efficiency figures. The requirement is not a minimum performance for each product, but the average of all the lighting in a building. It therefore depends upon the combination of lamps specified by the designer for that particular installation.

Richard Forster MSLL MCIBSE MILE IS a lighting engineer with BSRIA. Note that this article is based on the consultative documents not the final proposals.

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