Bright idea

At some time we have all experienced the dramatic effects that different lighting can have on our appearance. In some hotel bathrooms the sickly face staring back at us in the morning can make us wonder if it was wise getting up at all. Then, a few minutes later, under different lighting and in a different mirror, our face now looks healthy and reassures us that there is more to life than staying in bed after all.

In a hotel bad lighting can be a small inconvenience. But in a hospital good visual characteristics can make the difference between identifying a patient's ailment or missing it altogether. In other words, good lighting is crucial.

Fluorescent lamps are the mainstay of hospital lighting. They account for about 70% of all lamps used in healthcare installations; a typical hospital will have about 10,000 of them. They are an energy-efficient, low maintenance means to ensure the provision of the right light levels. However not all fluorescent lamps are the same, they vary in colour appearance, how warm or cool they appear when you look at them, and also in colour rendering - how well they allow you to accurately see the colour of the objects they light, as the earlier hotel room experience proves.

Extensive research has been undertaken to optimise the light provided by fluorescent lamps and to determine the required lighting for medical tasks and, in particular, the detection and medical diagnosis of cyanosis – the bluish discoloration of the skin caused by a drop in the oxygenation of the blood which can signify severe heart or lung disease.

It has been proven that reliable detection is possible, but only when the light source contains an appropriate power output in the red part (600 nm to 700 nm) of the visible spectrum. Too low an output in this area, a lack of red, will potentially lead to a diagnosis of cyanosis when this is not the case. Conversely, too high an output in this area may give the false impression of wellness and lead to true cyanosis being missed.

To resolve this issue, the Royal North Shore Hospital and School of Optometry at the University of New South Wales, Australia, carried out a series of trials with blood oxygen saturations ranging from 0.7% to 99.8%. From an analysis of the data the researchers produced a Cyanosis Observation Index (COI). The index defines the suitability of a particular fluorescent lamp. The requirement is that these lamps have a COI of less than 3.3. In addition to meeting the needs for good visual observation, and early and reliable diagnosis of cyanosis, this also makes it much easier to locate veins for injections and extractions.

Many existing fluorescent lamps do not meet the COI requirement, so new fluorescent lamps designed specifically to do so have been introduced, for example the Philips Optiview.

Legislation and market pressures are driving the increased use of COI-compliant lamps. In Australia and New Zealand the standard AS/NZS 1680.2.5 has been brought in to ensure conditions are suitable for the identification of cyanosis. The standard requires a colour-correlated temperature (or colour appearance) of between 3300 K and 5300 K, and a COI of less than 3.3. It also recommends all members of the healthcare team discuss and decide which locations should be used for the visual detection of cyanosis. Such areas extend well beyond wards, intensive care, and high dependency rooms into other areas where there is staff and patient interaction.

Although similar legislation is not yet in place in Europe a number of market drivers, such as the need to reduce energy use and avoid misdiagnosis, are set to change the way lamps are selected for hospitals.

As part of ongoing trials, lamps complying with the requirements for a correlated colour temperature and COI have been installed in the 2700-bed Gregorio Maranon hospital in Spain. To enable a comparison of the different lamps, photographs were taken before and following the re-lamping. Measurements of lighting levels were also taken and the staff were interviewed to gain their feedback. The feedback from nurses was positive and included statements such as “rooms appear cleaner”, “light levels and quality increased”, “patients’ veins are easier to see”, and “the working environment has improved and tasks are easier to perform”.

TNO Health, an independent consultancy specialising in the healthcare sector, recently undertook a survey into the effects of using these lamps. It concluded they improved the early diagnosis of conditions that can be detected by a change in skin colour and made medical tasks dependent on skin colour, such as finding veins for injections, easier.

Perhaps one day Europe will follow the example of Australia and New Zealand and make COI-compliant lamps standard in hospitals. Then maybe the lighting industry will turn its attention to developing a lamp to make us look good in hotel bathroom mirrors.