Any hospital complex encompasses a broad range of functional elements and is almost a self supporting community. The occupancy is both complex and dynamic and, therefore, any lighting has to meet the separate, and even conflicting, visual needs of staff, patients and visitors. Furthermore, many areas are in use 24 hours a day, seven days per week. Extending the natural working day is possible by electric lighting, but for hospitals the use of artificial lighting occurs to a much greater extent than in normal commercial and industrial premises. Recommended illuminations vary from one lux for night-lighting to 100,000 lux in operating theatres. The first objective is the provision of adequate illumination. Attempts to save energy by underlighting are a false economy, as without sufficient light errors and mistakes increase and visual fatigue reduces the rate of work. It is impossible to deal with all the lighting issues in a single article, so a small number of aspects have been selected. Their relative importance will vary from site-to-site, but hopefully it will be possible to audit local conditions either by a walk-through survey or by asking a few key questions of facilities management and procurement. Daylight This is a good starting point and immediately recognisable. Daylighting is an important element in building design, as it provides variety, a link with the outside world and a temporal scale. These aspects are particularly important for visitors and patients who are in an unfamiliar environment. Well-designed daylighting of a space can reduce the reliance on electric lighting, thus saving electricity. The inconsistency of natural light, however, often results in electric lighting being left switched on when it is not needed. In fairness to the occupants of a space there is no clear indication of the relative contribution from electric light and daylight by which a decision can be made to switch off electric lighting. The potential for daylighting to save energy is thus rarely realised. Lighting Controls There are various options available for the automated control of lighting based on presence detection, photo-sensors that can measure the amount of natural light, timers and building management systems. Which is deemed to be the most suitable will depend on the type of location and its usage pattern. There are two basic rules in providing automated switching. Firstly, there should always be safety of movement so occupants are never deprived of all lighting in a space and secondly there should always be a convenient local manual override so that the function of a space can continue. Lighting controls are called for in Part L of the Building Regulations for England and Wales, either automated or by local manual switching. For the latter, it is important that the switching circuitry relates to a sensible sub-division of the space. Large open spaces can be reorganised and it is important that the switching is changed to match the current arrangement. Manual switching does not have to be hard-wired and where change is likely switching by infrared handsets, similar to the domestic TV remote control, can be considered. Other options include switching via telephones or PCs. Sudden abrupt changes in lighting levels can be disturbing and even construed as a fault condition, so dimming is becoming more popular. With modern light sources, such as fluorescent tubes, the relationship between light output and power consumed is almost linear – dimming saves electricity consumption. With filament lamps, however, the light output decreases much more rapidly than the power consumption, so the potential for energy saving is less significant. Simple resistive dimmers do not save energy but merely transfer consumption from the lamp to the dimmer itself.
It is not normally appreciated that the greatest cost associated with lighting is the energy consumed. Typical through-life costs are shown in Figure 1. Changing from a normal nine-to-five, five-day week, to 12 hours per day every day doubles the hours of use and thus the energy consumed. For many situations in a hospital complex this may be a conservative estimate. Energy costs are currently predicted to rise after a period of stable, and even falling, prices. This is partially due to market forces, but concern about global warming and increasing environmental pollution is applying additional pressure to reduce energy consumption. It is, therefore, important that hospital lighting is based on only the most efficient light sources.
Fluorescent Tube Lighting
Probably the most common lamp in use today is the fluorescent tube. Developed just before WWII, its availability was restricted during the years of the conflict and became part of the post-war building programme. Significant technical progress was made in the 1950s with the introduction of improved phosphor coatings generically called ‘halophosphates’. There were two groups of white lamps for general lighting called white, warm white and cool white. Better colour rendering was possible if required, but only with approximately two-thirds of the light output. This group was given names such as Natural and Northlight. With this choice, good colour rendering was restricted to situations where it was important, such as retail premises and industrial colour matching. In the 1970s, new phosphors were introduced that created white light by the addition of red, green and blue colours and became known as ‘triphosphors’. These had three main advantages:
- Increased light output – typically +10% initially, 35% at end of life
- Good colour rendering – no longer was it necessary to compromise efficiency for colour rendering or vice versa. Colour rendering is explained in more detail below
- Good lumen maintenance
- Longer life.
This extra performance carried a cost penalty with triphosphor lamps at approximately twice that of their halophosphate versions. The construction industry has been traditionally structured so that through-life cost benefits are not properly recognised. The installing contractor is only interested in initial costs and not operating costs. The purchasing department compares component costs and favours low-cost replacement lamps. Facilities management can identify energy consumption, but have little opportunity to influence equipment specification. Higher lamp costs can be easily justified. More light emitted means less luminaires to purchase, fewer lighting points to install, lower installed load and less equipment to maintain. The better durability of ‘triphosphors’ results in the light output being maintained at a higher level for a longer period. The reduction in light output with time from the triphosphor lamp is only approximately 5%, which is not readily detectable by the naked eye. Consequently, if one lamp fails its replacement will not appear at different brightness. With halophosphate lamps there is a much greater fall-off in light output, which, after 9,000 hours, is approximately 20%. A single replacement lamp would be 25% brighter and would be apparent. This is why the curve for the halophosphate lamp is only shown to 9,000 hours – after that time group replacement becomes necessary in order to maintain a uniform appearance from an array of lamps. Recommended illumination levels are more accurately described as maintained or service illuminance, which does not refer to the initial performance, but the minimum average. This means lighting designers do not have to consider the initial light output from the lamps, but the lowest value when the lamp is replaced. The difference in light output, therefore, is not 10% but approximately 35%.
In addition to the phosphor efficiency the gas filling of the tube was altered so that approximately the same light output was possible with a reduction in power consumed. This can be identified by the change from 1 1/2 inch diameter to one inch. Lamp producers know this internationally as the change from T12 to T8. Many standard light bulb shapes are designated a letter – in this case T = tube – and its diameter is expressed in eighths of an inch. If any T12 lamps are found then it is likely that energy savings are possible. The only exception to this simple rule is 2,400mm (8ft) lamps, which are only available as T12. T8 and T12 tubes are physically interchangeable as they use the same bi-pin cap and are of the same length. In the 1990s, T5 fluorescent tubes were introduced. These use only triphosphor coatings and are designed specifically for high-frequency electronic operation. They will not retrofit into lighting designed for T8 or T12 lamps.
Electronic Control Gear
Operating fluorescent tubes at high frequency (circa 50kHz) will increase light output by approximately 10% compared with a standard 50Hz supply. Electronic circuits adjust the lamp power to give the same light output as conventional control gear, so the value branded on the lamp can be misleading. The use of T12 lamps and electronic gear is rare as availability started during the era of T8 lamps. The 36W lamp listed above would operate at approximately 33W. Electronic control gear has several significant additional advantages. The light is ‘flicker-free’ whereas lighting at 50Hz can cause discomfort to a small section of the population. It is also silent in operation and this can be important for certain hospital areas. Due to the fact that the starting process is controlled, the lamp life is extended to approximately 20,000 hours.
This is a key performance characteristic of fluorescent tubes. It is the ability of a light source to accurately represent the colours of an object, which it is illuminating. Colour is a complex subject but a colour rendering index (CRI) as a numerical scale 1–100 has been developed to provide an approximate indication. There are several versions but that commonly quoted by lamp manufacturers is Ra8, which is based on the average results from eight pastel shades across the spectrum, typical of normal interior surroundings. There are specific indices, of which one is based on skin colours, thus relating to medical visual environments. There is a European standard for surgical lighting, which suggests that the ideal colour temperature is 4,000–4,500 Kelvin. For tungsten halogen lamps, colour temperature and colour rendering are interrelated. For fluorescent tubes the characteristics are separate and a colour temperature of 4,000K should be specified in association with an appropriate CRI. Standard and deluxe triphosphor fluorescent tubes are normally acceptable for general lighting with CRI 80+ and for medical areas with CRI 90+. This aligns with the international and European standards for lighting of the workplace, which call for lamps with a minimum CRI of 80 for general areas and 90 for clinical areas. It is worth noting that compact fluorescent lamps are only available with triphosphor coating. Standard halophosphate lamps have a CRI of 50–75 so cannot meet these colour rendering criteria. Identifying which lamps are triphosphors is not simple, as manufacturers use individual brand techniques rather than generic descriptions. This has some justification as two lamps from different manufacturers may have the same CRI, but colours will not appear the same under both. As CRI is an average performance measure, so individual colours can differ, which is a limitation of presenting colour performance by a single number. To ascertain that the correct lamps are being used, it is necessary to determine that they are triphosphor and with a minimum CRI of 80 or 90 according to the location and that the lamps are provided by one manufacturer. Where colour is important there is no substitution for visual assessment of lamps in situ, which is not normally difficult to arrange.
Fluorescent lamps are now classified as hazardous waste and require appropriate disposal. The European Directives 2002/96/EC for Waste Electrical and Electronic Equipment and 2002/95/EC Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment were due to be implemented in UK legislation at the time of press. Lamps with high light output and a long life will help to offset the additional operating costs from these forthcoming regulations. Summary If the answer is no to any of the following questions, then energy saving measures can be applied.
- Where there is adequate daylight can the electric lighting be switched off?
- Have automated lighting controls been considered?
- Are the fluorescent lamps T8 or T5 diameter?
- Are ‘triphosphor’ lamps being used, with deluxe versions for examination areas?
- Is electronic gear being used? For most building services, efficient operation can only be confirmed by interrogating records and visits to plant rooms.
For lighting the answers to the above questions are there for all to see.