New light on warehouse and factory lighting
Fluorescent light fittings now offer a realistic and cost-effective alternative to HID luminaires for low bay and high bay lighting in warehouses and similar spaces. Simon Dixon explains why.
For many years, it has been traditional to opt for high-intensity discharge (HID) lamps such as high-pressure sodium (SON) or metal halide when selecting light sources for warehouses and other spaces with high ceilings. This tradition, however, fails to take account of the major advances that have been made in fluorescent light sources and fittings. As a result, a traditional high bay installation may also fail to deliver the maximum benefits to the end user.
Until relatively recently, there were very good reasons for choosing the high light output of HID sources, because of the distance between the fitting and the area where the light is required. With the introduction of the high-efficiency fluorescent lamp, however, comparable light outputs can now be achieved with considerably lower energy consumption and greater control flexibility.
To that end, luminaires with photometrics that are especially designed to maximise the benefits of fluorescent sources in low-bay and high-bay applications have now been introduced to the lighting market. Furthermore, these improvements can usually be achieved by replacing HID fittings with fluorescent fittings on a point-for-point basis, so no extra cabling is required.
An HID lamp can take up to 15 minutes to reach full light output, which makes switching in response to occupancy impractical. Similarly, most HID light sources cannot be dimmed, so there is no potential for control techniques such as daylight linking. In contrast, fluorescent lighting will re-strike immediately and can be dimmed whenever needed, so there are many more control options.
In a warehouse environment, these control strategies would typically include occupancy detection in aisles that are only used occasionally. Where daylight enters the building the lighting can also be set to dim as appropriate to maintain the design illuminance.
Just as importantly, considerable reductions in installed electrical load can be achieved without compromising on lighting quality. A 400 W SON or metal halide lamp can be replaced by a 4 x 40 W or 4 x 55 W fitting to give a better colour appearance and better colour rendering. In this respect, it is important to take note of ballast losses; a 400 W SON using wire-wound control gear, for instance, will run at 460 W.
Fluorescent lighting also offers greater flexibility in tailoring the lighting design to the needs of the space or, even, different zones within the space. For example, fluorescent tubes in a wide range of colour temperatures and colour-rendering properties can be selected to suit the activity in each zone.
Putting theory into practice
These and other key benefits are illustrated by a feasibility study recently carried out for supermarket chain Netto. Following a significant increase in electricity tariffs, the company decided to explore options for re-lighting its warehouses, beginning with the main warehouse in Yorkshire. Netto’s criteria were to reduce energy consumption and create an improved lit environment with minimum cost and disruption.
The solution involves replacing HID fittings with 4 x 55 W fluorescent fittings, using 4000 K colour temperature tubes on a point-for-point basis. They will be controlled via integral occupancy and daylight sensors to minimise running hours, resulted in projected savings around £50 000 per annum on energy alone. The ability to include integral emergency lighting in the fluorescent fittings also means there is no need for a separate emergency lighting system, as would be the case with HID lighting.
Further savings will be achieved through lower maintenance costs as the fluorescent tubes offer a life of 16 000 h before re-lamping is required, compared to around 9000 hours for HID lamps. Using multi-lamp fittings also means that a single lamp failure will have a minimal effect on light levels in the area, and re-lamping can be scheduled for a convenient time. When single-lamp HID fittings fail, light levels in a wide area fall dramatically so the lamp has to be replaced immediately to maintain a safe working environment.
Additional benefits from the new lighting scheme will include fewer picking errors due to poor colour rendering. The new scheme offers excellent colour rendering so that staff can clearly differentiate between different coloured labels.
Just as importantly, staff at Netto will enjoy a more comfortable working environment and the feedback on the ‘mock-up’ area has been very positive.
Many warehouses have been forced to compromise on their lighting in the past because of the limitations imposed by the light sources available. Modern fluorescent light sources, combined with fittings that optimise light distribution, have addressed these limitations so it really is time to take a fresh look at what can be achieved, while offering the end user best value and low cost of ownership.
Simon Dixon is with Riegens Lighting.
