Key Considerations when Lighting for Data Centres

Lighting in data centres requires careful consideration beyond simply achieving the recommended illuminance levels. A typical design objective is to provide approximately 500 lux on the horizontal working plane, generally at floor level within equipment aisles, together with around 200 lux on the vertical faces of server racks and cabinets where technicians carry out maintenance, inspections and equipment changes.

Good vertical illuminance is particularly important because technicians frequently need to read labels, identify connections, inspect equipment and work on the front and rear faces of server racks rather than on conventional horizontal work surfaces. The lighting layout should therefore be designed to provide adequate illumination between racks and avoid excessive shadows caused by tall equipment cabinets.

One of the most significant challenges when selecting lighting for data centres is the elevated ambient temperature that can occur within server halls. High-density IT equipment generates substantial heat and, although cooling systems are designed to maintain suitable operating conditions, localised hot spots and elevated temperatures may still occur, particularly within hot aisles, above server racks and close to equipment exhausts.

Elevated ambient temperatures can have a direct effect on the performance and service life of LED luminaires. LED modules rely on effective thermal management to control the temperature at the LED junction. When luminaires operate in higher ambient temperatures, the internal temperature of the LED modules and electronic control gear also rises. This can accelerate lumen depreciation, reduce driver life and shorten the overall operating life of the luminaire.

It is therefore important to specify luminaires that have been tested and rated for the anticipated ambient temperature. Standard commercial luminaires are often designed around an ambient temperature of 25°C and may not be suitable for continuous operation in warmer data centre environments. The manufacturer’s declared ambient temperature rating, commonly identified as the Ta rating, should be checked carefully during product selection.

The thermal performance of the luminaire body and optical materials must also be considered. Many LED luminaires use thermoplastic diffusers, commonly manufactured from materials such as polycarbonate or polymethyl methacrylate. A critical material characteristic is the glass transition temperature, known as Tg.

The glass transition temperature provides an indication of the temperature range at which an amorphous thermoplastic begins to lose rigidity and becomes increasingly flexible. It does not represent the melting point of the material. Instead, it marks the transition from a hard, glass-like condition to a more compliant, rubber-like state.

As the temperature approaches or exceeds the Tg, the diffuser may become more susceptible to deformation, sagging or distortion, particularly where it is subjected to its own weight, internal stresses or mechanical loading. Prolonged exposure to elevated temperatures can also accelerate material ageing, discolouration and changes in optical performance.

Designers should therefore confirm that the diffuser material is suitable for the expected operating temperature and that the complete luminaire has an appropriate declared ambient temperature rating. Consideration should be given not only to the general room temperature, but also to localised temperatures within the luminaire and in areas affected by heat discharged from server equipment.

Emergency lighting requires particular attention. Many self-contained emergency luminaires incorporate integral lithium-ion, nickel-cadmium or nickel-metal hydride batteries. Battery performance and life are highly sensitive to temperature, and continuous operation above the manufacturer’s recommended ambient temperature can significantly reduce battery capacity and service life.

A battery intended to provide several years of service under normal conditions may require replacement much sooner if it is continuously exposed to elevated temperatures. High temperatures may also reduce the available emergency duration and increase the risk that the luminaire will fail to achieve its required backup period during testing or a mains power failure.

For this reason, designers should carefully assess whether self-contained emergency luminaires are appropriate within the server environment. On larger data centre projects, a centrally supplied emergency lighting system may provide a more reliable solution. Alternatively, emergency battery packs may be remotely located in cooler plant rooms, service areas or circulation spaces where they are less exposed to heat.

These approaches can reduce thermal stress on batteries, improve system reliability and simplify maintenance and replacement. The emergency lighting strategy should be developed in accordance with the relevant requirements of BS 5266 and coordinated with the wider fire safety and electrical resilience strategy.

Other important lighting considerations include glare control, maintenance access, circuit resilience and energy efficiency. Excessive glare or reflected brightness from equipment cabinets can make maintenance work uncomfortable and reduce the visibility of labels and indicator lights. Luminaires should therefore provide suitable light distribution and good visual comfort without creating excessive contrast.

Lighting circuits may also need to be segregated to maintain partial illumination during faults or maintenance. Products should be selected for low maintenance, long service life and ease of replacement, while high-efficacy luminaires should be used to minimise additional electrical load and heat gain within the conditioned space.

Careful coordination is required with cable trays, busbars, containment systems, cooling equipment, fire detection systems and fire suppression installations. The lighting layout should avoid physical conflicts and ensure that luminaires remain accessible for inspection, cleaning and replacement throughout the life of the facility.

In summary, a successful data centre lighting design should provide approximately 500 lux on horizontal working areas and 200 lux on the vertical faces of server racks where technicians carry out detailed work. However, illuminance alone is not sufficient. The elevated thermal environment is a defining consideration and can affect LED modules, drivers, emergency batteries, luminaire housings and thermoplastic diffusers.

Specifying luminaires with suitable ambient temperature ratings, appropriate diffuser materials and a carefully considered emergency lighting strategy is essential to maximise reliability, maintain optical performance, reduce maintenance costs and ensure long-term compliance.

Finally, it is recommended that an experienced lighting designer is consulted when designing lighting systems for data centres or any other specialist application. Lighting design is a highly specialised discipline, requiring an in-depth understanding of photometry, visual performance, optics, controls, emergency lighting, material science, energy efficiency, maintenance, standards and the interaction between light and the built environment. Whilst electrical engineers possess extensive expertise in power distribution and electrical infrastructure, specialist lighting designers focus exclusively on achieving the optimum lighting solution and therefore offer a depth of knowledge that extends well beyond the lighting aspects typically encountered within general electrical design. Engaging a specialist lighting consultancy such as Lumenata at an early stage of a project can help ensure that lighting installations are not only compliant with current standards but also deliver optimum performance, reliability, energy efficiency, maintainability and whole-life value. This collaborative approach can reduce project risk, avoid costly design changes and provide clients with confidence that the lighting system has been designed using industry best practice by specialists dedicated solely to the science and art of lighting.