Seeing upgrades in the right light
With so many organisations upgrading their lighting to reduce energy consumption, building-services engineers have an important role to play in ensuring end users get the optimum system. Simon Dixon of Riegens Lighting considers the options
Next year (2013) we are due to see another revised edition of the Building Regulations. From the recent consultation with the lighting industry, it is clear that Part L 2013 will continue to promote more efficient lighting. It is also highly likely that it will focus on both increasing the lower limit for luminaire efficacy (the technology requirement), and propose use of the Lighting Energy Numeric Indicator (LENI) as an alternative to the technology requirement.
In practical terms this means that specifiers will need to consider the overall efficiency of the system in terms of lumen output and how the lighting is controlled. Effectively, the new regulations will be looking for a meaningful way of measuring how the lighting is used. Also, as the Building Regulations apply to major refurbishment as well as new build, these changes set the scene for lighting upgrades.
In parallel, of course, there is the general principle of delivering the best result for the end user, irrespective of whether particular regulations apply. And doing so entails making use of the most appropriate lighting technologies for the project in hand.
Currently the lighting technology with the highest profile is the light-emitting diode (LED), and LED lighting certainly has a key role to play in reducing lighting energy consumption in some applications. But that doesn’t mean LED is a universal panacea. In fact, there are many situations where upgrading to high-efficiency T5 fluorescent light sources in luminaires that have been optimised for T5 — and combined with effective controls — will offer the best all-round solution.
One reason for this is that the return on investment is particularly important in these straitened times where organisations are reluctant to invest in building improvements unless they can see a reasonably quick payback. With LEDs the criterion that mitigates against a fast payback is the cost of the lamps — typically 10 times that of a linear or compact fluorescent lamp. LED luminaires also tend to be expensive compared to fluorescent luminaires, simply because of the economies of scale in relation to the volumes sold.
|Office lighting is typically replaced every six to seven years, so capital cost needs to be related to projected life.|
In the light of this high price differential, it takes a significant reduction in energy costs to compensate sufficiently to deliver a fast payback. So clearly the type of lamp that is being replaced in the refurbishment is important. If a 50 W halogen lamp is being replaced with a 7 W LED the reduction in installed electrical load will deliver an impressive return on investment — or at least one that is acceptable to the financial director.
This situation is quite different when replacing fluorescent light sources with LEDs. Indeed, there are some 600 mm-square LED fittings on the market that will consume as much power as a 600 mm-square fluorescent fitting.
In such case, other factors come into play; an obvious factor is the reduction in maintenance costs resulting from the longer lamp life of LEDs. Most LED drivers have a rated life of only 20 000 h, which means they are not a ‘fit-and-forget’ solution. Some LED manufacturers also claim a 45 000 h life for their lamps, which is certainly impressive. However, there are also special premium T5 lamps that claim the same. And the standard T5 lamps from quality manufacturers will deliver nearly 20 000 h.
In these circumstances it is necessary to calculate whether the maintenance savings sufficiently offset the extra cost of the LED lamps. For example, office lighting is typically replaced every six to seven years, so it is worth questioning the value of a high-capital-cost installation in relation to its projected life. In retail applications the life of the lighting is likely to be more like two to three years before the store gets a make-over, so there may be even less justification.
Of course, not all lighting upgrades are even suitable for LED lighting because of the light outputs that can be achieved. For instance, a 4 x 55 W T5 fitting will provide a comparable light output to a 400 W high-pressure sodium (SON) lamp. So replacing SON with T5 in a high- or low-bay installation will provide an immediate reduction in energy consumption. It will also facilitate improved control, so that even greater savings can be achieved — in line with the move towards a LENI-like approach to evaluating lighting efficiency that was discussed earlier.
Therefore, as has always been the case, each project needs to considered in its own right. The important thing is not to be blinded by the hype but to apply sound engineering principles to each job.