The speed of light

One of the trends that nearly always accompanies an economic downturn is that more organisations decide to refurbish their existing premises rather than move to new premises. Or they may choose to delay any action altogether.

Where the current situation differs somewhat from previous downturns is that there is unremitting pressure on organisations in all sectors to reduce their energy consumption and carbon footprint. So they need to start thinking about the smartest ways to address both issues.

For example, it’s clear that the lowest cost option for upgrading lighting, and therefore the one that offers the fastest return on investment, will be to replace existing light sources with more efficient lamps, taking advantage of recent advances in lamp technology. High intensity discharge (HID) lamps such as metal halide and high pressure sodium provide a case in point.

Here, I would urge any specifier to be thorough in assessing the available options and to take account of both lamp and ballast operation to provide the full picture and arrive at the best solution.

For instance, if a particular project requires a 35,000 lumen package to meet design requirements; this can be achieved by using a cheap 400W metal halide lamp using equally cheap control gear. Taking ballast losses into account, that’s an electrical load of about 485W per lamp.

Or, the same lumen package could be achieved with a higher quality 350W lamp with better control gear that provides just 25W ballast losses – giving a saving of 110W per lamp without compromising on lighting quality. In fact, newer lamps will also give improved lumen maintenance so lighting quality will be improved over the life of the lamps.

Similarly, there are now 200W metal halide lamps that can directly replace older style 250W metal halide lamps to save 66 circuit watts, or 28% energy consumption per fitting (including control gear losses).

Taking this principle a step further, even greater savings can be achieved when high pressure sodium or mercury vapour lamps are replaced with metal halide. For example, a modern 200W metal halide lamp will give the same light output as a 400W mercury vapour lamp, resulting in a 49.6% energy saving.

As well as highlighting the benefits of opting for the newer designs of HID light source, these examples also illustrate the importance of ballast losses and how much these can vary.

Again, price often plays a key role in this decision making process and in the case of control gear there is generally a direct correlation between price and quality of manufacture and the materials used. This is particularly true in the current market conditions where the prices of copper and steel have been rising considerably and some manufacturers have resorted to skimping on materials to keep their prices down. Unfortunately, these materials have a direct impact on the efficiency of the control gear so a ballast that costs 25p less than a higher quality model could add as much as 55W electrical load to each light fitting.

Until relatively recently, buildings using metal halide lighting have been unable to take full advantage of the control options available for minimising energy consumption. This is because HID lamps couldn’t be dimmed and they are unable to re-strike immediately after being turned off.

This situation has now changed with the introduction of advanced electronic ballasts that allow these lamps to be dimmed. As a result they can be dimmed in relation to occupancy and daylight levels. For example, in a warehouse the lighting in unused aisles can be dimmed to a minimum light output and then be immediately ramped up when someone enters the aisle. Similarly, where daylight is entering the space the lighting can be dimmed while still ensuring the design illuminance is maintained.

All of these issues impact on cost of ownership – another key consideration for any organisation. So, for example, higher quality lamps don’t just offer improved energy efficiency, they also offer longer lamp life. This is particularly significant in areas where luminaires are difficult to access for re-lamping and where such maintenance is expensive and disruptive. Longer lamp life also means that fewer lamps are disposed of under the WEEE Directive during the lifetime of the installation.

For all of these reasons, I believe that anyone involved in specifying HID lighting needs to make a conscious effort to consider all of the options available, rather than simply doing what they’ve always done. In fact, this is the only way that end clients will get the best solution with the best value.

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