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Retrofit for purpose

Retrofit for purpose

With ever increasing energy costs and an emphasised focus on green credentials, the push for efficient operations is now higher than ever. This is something that is true across all industries, but the opportunities for energy reduction, and therefore the approach which one should take to achieve this goal is something that often varies between cases.

However, one theme which can be seen time and time again is lighting.

Lighting of car parks (or any other space) frequently represents one of the largest ongoing operating costs. With regular leaps forward in technology the latest products on the market can be used to drastically cut these to a fraction, leading to the obvious question: is it better to upgrade now, or wait until the next technology becomes available?

So what is the best way to reduce lifetime installation costs and carbon footprint? Upfront costs, and indeed the energy embodied within the materials, manufacture, transportation and installation of the units, can account for significant proportions of the life time costs. For this reason a smart upgrade strategy is required to ensure that only the outdated components are replaced – in other words, a retrofit upgrade strategy.

In the context of lighting products, a retrofit is a product which is compatible with an existing system and that has an offering above and beyond that of what it replaces. Retrofitting presents an opportunity to take advantage of new technologies without incurring the need for full fitting replacement, and in many cases in the form of a direct lamp replacement (requiring no rewiring or modification to the existing circuit). In fact, retrofitting is by no means a new idea – the use of metal halide lamps to replace sodium is a good example where benefits were achieved from a simple retrofit solution.

Fittings are generally made up of three main parts; the housing, the light source (the lamp, or LED) and the ballast or driver. While the housing is generally a low tech part which has the potential to age as well as Carol Vorderman, the latter two of these exhibit increases in performance over time due to innovations in the industry. Innovations can be both transformational (which is usually attributed to a technology change such as that from fluorescent to LED) and incremental (which is driven by small gains in efficiency, attributed to improvements in existing technology or production processes).

Technology Adoption

Generally there are leaps in performance associated with transformational changes. Conversely, incremental changes usually provide regular improvements which push up efficiencies. A new technology does take time to overtake the incumbent technology in terms of performance and this is where patience is required. Remember when Apple tried to push the Newton as a PDA device in 1993? Due to the bulkiness and price it was not thought to offer performance benefits over using a paper diary, so it fell flat. The people who did buy in at this stage were doing so not for performance benefits but because they were technology enthusiasts (these individuals form part of the “early market” described by Geoffrey Moore in his book Crossing the Chasm). Once a technology presents immediate performance benefits (rather than the promise of performance benefits in the future) its chances of being adopted by the mainstream market soars. In recent years LEDs have broken through this market barrier. Cast your mind back to 10 years ago when the latest LEDs were offering 60 lumens per watt, compared to over 200 lumens per watt today[i].

Figure 1 Technology adoption curve

Figure 1 - Technology adoption

With these ever increasing performance possibilities comes an opportunity to replace the light source and/or driver within the existing luminaire in order to reap financial benefits, securing a return on investment for the purchaser. If each time we wanted to do this we had to replace the luminaire too, then the incentives would be lower.

Figure 2 Performance improvements with new technologies

Figure 2 - Performance improvements>

Embracing this philosophy can be done by following a retrofit strategy from the outset – investing in retrofit-friendly fittings with the intention of upgrading the ‘inners’ on a more regular basis than the luminaire. Broadly speaking it is a strategy regarding asset utilisation which ensures maximum value and enables flexibility in terms of future technological developments or changing requirements. It ensures that there is always an option to upgrade to the latest performance level at a low cost.

Retrofit product design

If it is as simple as that, then why isn’t everyone retrofitting?

Designing a new technology into a retrofit form adds complexity. The main thing about any electronics is to design the system to ensure a suitable operating temperature to prolong the life of the product. The starting point of any design must therefore be the matter of heat management which can be more difficult when designing retrofit products because there is usually no direct conductive thermal path to the outside environment. Nevertheless, by using thermal simulations and carrying out thorough thermal tests in a variety of closed fittings, it is possible to be confident that the operating temperature of the LED chips is well within the range set by chip manufacturers to ensure long life operation.

Another area where careful consideration is required is the matching of optical performance. The photometry of a fluorescent tube differs from that of an LED retrofit tube. However, as will be discussed below, when it comes to fitting efficiency this factor usually works to the LED retrofit’s advantage.

There are also a number of common misconceptions regarding the use of LED retrofits ranging from financial concerns to compliance and re-certification issues.

Provided that the retrofit lamp is certified for its intended purpose then there will be no requirement to re-certify the fitting once it is installed. In the same way that you do not need to recertify your bedside lamp when a CFL is used in place of a filament bulb, there is rarely the need to do so when using LED tubes in place of fluorescents.

Lifetime costs

Financially speaking, the use of LED retrofits does pay off. Savings are highest in installations where access to the fitting is difficult and using longer life technology allows for fewer lamp changes. Shae Gilbert, lead engineer of lighting and innovation at London Underground recently explained how the use of LED lamp retrofits is saving millions on maintenance bills. Changing a single tube over an escalator can cost nearly £1,000 so the return on investment once a lamp change is avoided is phenomenal[ii]. Huge savings can be achieved in other areas where maintenance costs are high, for example where traffic management is required in tunnels, underpasses and subways.

Maintenance costs aside, energy savings are typically 50% of the fluorescent system wattage to attain the same brightness, meaning a return on investment can be achieved even in scenarios where lamp replacement costs are negligible. Consider a 58W fluorescent lamp on magnetic gear (circuit wattage 65W) being replaced with a 30W LED tube. At a conservative energy cost of £0.10/kWh the saving per hour of operation is 0.35 pence, meaning even after only 20,000 hours of operation (a fraction of the rated life for high quality LED tubes) the savings in energy equate to £70; this by far exceeds the cost of the LED lamp.

Improved performance

Understandably, at this point you will be asking how it is possible to achieve a 50% reduction in energy usage while maintaining the brightness levels when fluorescent lumens per circuit watts is around 75 and that for LED tubes is typically 105. One of the reasons relates to fitting efficiency, or light output ratio.

Figure 3 Diagram showing LOR principle


Fluorescent tubes emit light from the entire circumference of the lamp, meaning reflectors must be used to direct the light emitted from the ‘back’ to the desired area. Inevitably, this optical control introduces inefficiencies. What’s more, over time particulates become deposited on the surface meaning even less of the light directed into the fitting is reflected. Typically a reflector for an external fitting (such as those used in subways) is made from basic sheet metal of low reflectivity so the losses are significant. LEDs, however, only emit light from one surface of the tube which means there is no reflectance within the fitting.

The extent of this change in fitting efficiency can be estimated by scaling measured average lux levels by the lumen output of the lamp using fluorescent lamps and then again for the same installation using LED lamps. Using a real life subway installation the LOR was calculated to have improved by 59.4% after switching to LED retrofit lamps (see Figure 6).

On top of this there is the quality of light to take into account. Using white light from LEDs to replace standard warm or cool fluorescent lamps increases the perceived brightness per watt and this is what is important when it comes to safety and comfort. It is widely accepted that this is a valid approach, as acknowledged in Annex A of BS 5489-1:2013 and ILP PLG03 [34]. The SP ratio of a cool white fluorescent lamp is approximately 1.48, whereas a white LED lamp can be over 2 (exact value dependant on manufacturer and binning)[iii].

By combining these three improvement areas (higher lumens per watt, improved fitting efficiency and a greater SP ratio), it is easy to see how significant energy savings can be achieved.

Health concerns

A topical issue that has attracted a great deal of discussion and coverage in the industry has been that of health and safety in relation to light sources.

Mains power in the UK is supplied at a line frequency of 50Hz. Since the waveform is approximately sinusoidal there will be two points in the cycle for which the voltage supplied is 0, giving rise to the phenomenon of flicker and light output modulation.

Fluorescent tubes running on magnetic gear modulate at 100Hz (relating to the two points on the mains cycle where supplied voltage is 0) and towards the end of life a severe modulation of 50Hz and below can be introduced.

Studies investigating the effect of flicker on patients with photosensitive epilepsy (which represents approximately 1 in 4,000 of the population) indicate that flicker in the range ~3 – ~70Hz represent a risk of seizure[iv]. The electroencephalographic recordings from patients during the study highlight around 50% of patients responded to a flash frequency of 50Hz[v].

Importantly, LEDs do not exhibit a 50Hz flicker towards the end of life. A 100Hz modulation is usually present for mains connected LED circuits, but depending on the driving circuitry it can be reduced or entirely removed (for LEDs driven with a continuous direct current).

There is also the added benefit that the LED retrofit doesn’t make use of glass or a mercury vapour, which is a cause for concern when a breakage occurs perhaps during cleaning or a lamp replacement.

LED retrofits in action

The introduction of new technology on the market is usually met with scepticism and perceived risk. Once the performance and price reach a point where there is a clear opportunity for savings, and large installations have been implemented and proved to be successful, this perceived risk will invariably diminish.

The time for LED retrofitting to shine has now arrived. The performance of LEDs has been improving rapidly over recent years and LEDs are now able to offer significant benefits over older technologies. Confidence in the technology has increased considerably, giving rise to regular announcements from large companies and organisations that they are making the switch to LED sources.

One such installation is Captain Cook Square car park in Middlesbrough. INDO Lighting supplied over one thousand T8 LED retrofit tubes to be installed into the multi-story building, providing attractive returns for the car park owner. In addition to these financial benefits, the quality of light improved, allowing greater colour recognition and increased brightness. Figure 4 shows the visual improvement, which can be explained by the gains in lumen efficacy, SOP ratio and LOR as discussed earlier.

Figure 4 Before (left, fluorescent) and after (right, INDO LED) photographs from Captain Cook Square car park

Figure 4 - Captain Cook before v after

Following the LED installation (carried out in Q1 2014), electricity metering showed a reduction in the total building energy consumption (including lifts, barriers, security systems etc.) of 45%. This is a monthly reduction of around 13,000 kWh. Figure 5 shows more details.

Figure 5 Whole-building monthly energy consumption compared year on year.

Figure 5 - Captain Cook energy

Large installations of INDO LED retrofits have been carried out across London Boroughs with extremely positive results. An independent report carried out within a subway installation at Westminster commented that the LED retrofits had notably improved the appearance of the space as a whole. Key metrics from the report, including an analysis of the results are shown in figure 7.

Figure 6 Westminster: INDO LED lamps (30W circuit, left) next to fluorescent lamps (84W circuit, right)

Figure 6 - Westminster LED vs Flu

Figure 7 Summary of performance results from test installation

Figure 7 - Installation results

[gdlr_quote align=”center” ]Illumination per circuit watt and illumination per lamp lumen relate to average illumination levels and are calculated from a test subway installation where an independent lighting survey was carried out for fluorescent T8 lamps and for INDO LED T8 lamps. The measurement grids used to carry out the survey were in accordance with ILP Technical Report 28 ‘Measurement of road lighting performance on site‘.und benefits[/gdlr_quote]

The general performance of LEDs is ever increasing and a new technology is always around the corner. Retrofitting with the latest technology at a low cost provides flexibility as it ensures that there is never a lock-in to current technology levels. If an improved product is launched a few years after installation there will not be the need to write off costly fittings to upgrade.

Combining revolutionary LED technology with this pragmatic retrofitting philosophy is undoubtedly a smart way to exploit the current technology landscape to improve lighting standards and drastically reduce installation lifetime costs.



[i] Miller, H. (2010) Creative Destruction, With a Nudge from the Top, [Online], Available: [27 Nov 2013]

[ii] Bain, R. (2013) ‘The light at the end of the tunnel’, Lux Magazine, Issue 31 – November 2013, pp. 54-59.

[iii] Lighting Research Center (2009), Outdoor Lighting: Visual Efficacy, Vol. 6, Is. 2, p. 6

[iv] Wilkins, A., Veitch, J. and Lehman, B. (2010) LED Lighting Flicker and Potential Health Concerns: IEEE Standard PAR1789 Update [Online], Available: [27 Nov 2013]

[v] Wilkins, A., Veitch, J. and Lehman, B. (2010) LED Lighting Flicker and Potential Health Concerns: IEEE Standard PAR1789 Update [Online], Available: [27 Nov 2013]