Lux magazine introduces the Lighting Economist, Dave Tilley. His job is to work out the maths of lighting and energy – so you don’t have to. This month Dave solves a common problem: what’s the most cost-effective retrofit for low voltage halogen?

Once, not so long ago, the low voltage MR16 lamp was sex on a stick. Now it’s an embarrassing energy-guzzler that’s a whisker away from being banned.

So you want to replace them with a retrofit lamp. Good idea. But what to choose? The range and diversity of efficient light sources has increased exponentially over the past few years, making the selection process more complex than ever.

Retrofit lamps can deliver significant energy and, crucially, maintenance savings.

There are a few fundamentals that may seem obvious, but are important to remember when specifying retrofit lamps. • Lamp manufacturers need to sell lamps. • The information provided will only apply to the lamp. • The information will often apply only to the most favourable application, such as residential. • Return-on-investment calculations often ignore system wattage and the cost of installation.

What do we mean by retrofit?

This accepted, there’s also the definition of retrofit. Lighting specifiers expect a retrofit lamp to replace the existing lamp without having to make changes to the luminaires.

This includes the lamp holder. This requirement alone will reduce the number of lamps that manufacturers can claim to be retrofit.

Although significant efficiencies in energy and maintenance can be achieved by using retrofit lamps it’s important to balance efficiency with application.

OK, let’s get started on a real-world installation. This example is based on an installation comprising 30 50W MR16 low voltage dichroic lamps. Let’s compare it with a range of possible retrofits (see Table 1). The calculations are based on annual operation of 4,200 hours and electricity priced at £0.10 per kilowatt hour. For instance, one 50W MR16 will consume 210kW hours and cost £21 a year. A lot compared to its purchase price of about £1, isn’t it?

So on this calculation, LEDs provide the best energy savings over product life. But this table doesn’t include the cost of the lamp itself and how often it has to be replaced. So let’s take a typical five-year timeframe and now include the cost of the lamp and replacements (see Table 2).

Now the calculation demonstrates that over five year:

the 11W CFL has the edge, if you want to achieve the equivalent light output as the original MR16. Would it therefore be reasonable to conclude that the 11W CFL should be the lamp of choice to replace 50W MR16? The short answer is no. There are a number of important factors to consider, most important of which is the application. Also the interaction and balance with the remaining light source must be considered. The cost saving relating to maintenance efficiency is dependent on the maintenance regime. If maintenance

failed lamps, the cost of replacement, the employee’s time, is rarely included in any financial calculations and statements. Also the practice of using staff to change lamps contravenes health and safety regulations.

If staff are used to replace lamps there are a number of points to be considered.

• Health and Safety legislation could be compromised. • Lamp life can be reduced due to poor handling. • Wrong lamps can be installed. • Where it is not a lamp issue the problem is not resolved.

Disguised costs

When managers use local electrical contractors the true cost of lamp replacement can be disguised due to poor financial records, payment made from petty cash, job combination and inadequate administration records.

A realistic cost for reactive lamp maintenance is based on a call-out charge and hourly rate. A call-out charge from a qualified electrician will be a minimum of £75. Therefore the minimum cost of a lamp change will be £3. This assumes that 20 lamps are changed during the visit which is unlikely because the store or premises would be poorly illuminated.

Where reactive lamp maintenance is used a more realistic figure of £6 per lamp replacement should be used.

The cost of a new lamp holder or new luminaires will only extend the ROI by 12 months. This means that the overall ROI through the implementation of any of the lamp types shown, with the exception of the 20W CMH, will be 24 months or less.

The Lighting Ecomomist’s verdict

Is there a retrofit lamp that is the best in class and the obvious solution? The simple answer is no. If a true retrofit lamp is required then the IRC range meets the criteria of a straight replacement with no extra work. In fact the question is: why would anyone choose a standard 50W MR16 over an IRC equivalent?

My recommendation is to replace the low voltage halogen with a CFL with a GU10 twist-and-lock base in either 11W or 14W, such as Megaman’s. It’s cost effective but you have to be prepared to change the luminaires as well.

The LED lamp is, however, getting better and costs are coming down. And one day soon it will suddenly become the retrofit lamp that the manufacturers currently claim; that is until they launch their new and improved version three months later.

Simple savings

Saving energy need not be a complicated affair, and in the current economic climate, the time is right to consider the simplest of energy-efficient retrofits. Dave Tilly does the sums

The low down on low bays

Lighting Economist Dave Tilley turns his attention to a specific retrofit application this issue – warehouses. How do the alternatives to the ubiquitous HID low bays stack up?