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LED lighting and patients’ health
Dr Cosmin Ticleanu from the Building Research Establishment (BRE) analyses the impact of LED lighting on patients’ health and well-being
Lighting can affect the health of people in buildings. This goes beyond the safety aspects of providing enough illumination to see by; lighting affects mood and human circadian rhythms, while poor lighting can cause glare, headaches, eyestrain, aches and pains associated with poor body posture. This is particularly important in healthcare settings where patients are already ill.
Lighting using light-emitting diodes (LEDs) is relatively new compared to other types of lighting, and it is important to consider any potential impacts on the health of patients whenever LED lighting is installed. A first requirement is to ensure adequate lighting with good colour rendering so medical professionals can do their jobs properly. Being directional by nature, LEDs can be very bright and glaring. Some very bright LEDs may cause retinal damage if viewed directly. LEDs can exhibit flicker, which can cause headaches, eyestrain or epileptic seizures in susceptible patients. Night-time exposure to bright sources rich in blue light, such as some types of LED, can alter the body clock and lead to various health problems. LEDs also have benefits compared with other conventional types of lighting, as they do not contain mercury, have lower human toxicity potential, and emit little or no UV.
Recent increases in luminous efficacy of LEDs have led to LED lighting providing similar or even better energy efficiency compared with conventional types of lighting. The long lifetime of LEDs offers additional benefits by reducing maintenance costs and minimising disruption associated with re-lamping in continuously occupied areas. However, LED lumen output and light distribution may differ from those of conventional lighting. In retrofit applications, like-for-like replacement of conventional lighting with LED lighting may not provide optimum results, and replacing the entire system can be the better option. For new spaces, a dedicated LED lighting system designed to standard recommendations is recommended.
When using LED lighting, enough light should be provided on both horizontal and vertical surfaces. Typically, LEDs do not fail at the end of their lifetime but their light output drops below a specified level. The lighting design should use the appropriate maintenance factor for the LEDs so that the light levels achieved throughout the life of the installation do not fall below the recommendations. Where LED downlights or LED tubes are installed, additional light should be provided on reflective surfaces to illuminate the ceiling and walls and to soften shadows on people’s faces. LED task lights should give enough light and cover the whole task area.
Colour rendering defines the ability of a white light source to render object colours accurately. It is therefore essential for clinical diagnosis. LEDs come in a variety of spectral outputs and colour rendering performance, and the installed LEDs specified need to meet or exceed the minimum standard recommendations for colour rendering.
Glare from LED lighting
Human eyes can adapt to a wide range of light levels from almost total darkness to very bright scenes. However, excessive light levels and luminance contrasts can lead to glare.
LEDs are typically small, directional light sources, which can be very bright and glaring unless they are appropriately positioned or incorporated within luminaires with shielding elements or diffusers to reduce or avoid glare. Diffusing LED panels may be a source of glare if they appear bright when viewed from a shallow angle, but LED luminaires have become available that have good glare control. Sometimes retrofit lamps may cause glare because of the optics of the luminaire in which they are inserted. LED luminaires need to be set up to avoid a direct view of the lamp by patients and to avoid reflection in glossy surfaces such as portable device screens.
Optical hazards from LEDs
Exposure to too bright light, besides leading to glare, may cause particular damage to the eye. The type and extent of damage depends on the brightness (luminance) of the light source, its angular size (which partly depends on how far away it is), its spectrum and the duration of exposure.
Generally, short wavelengths (UV and blue) are the most damaging. The cornea, conjunctiva and lens are most sensitive to UV radiation. The retina is more likely to be affected by blue light, since UV radiation tends to be absorbed by the rest of the eye, particularly the cornea and lens, before it reaches the retina. Only about 1 to 2 per cent of the longer wavelength UV radiation, UVA, reaches the retina.
Although LEDs emit little or no UV radiation, they can form a very bright light source with high blue light content, and some types of high power LED can cause retinal damage if viewed directly. This can be judged from the risk group of the LED lamp. Lamps in the exempt risk group or risk group 1 (low risk) are unlikely to cause problems.
Flicker is generally defined as a rapid and repeated change over time in light brightness. The eyes are particularly sensitive to flicker, which is mainly perceived towards the edges of the visual field. Depending on individual sensitivity, flicker can have effects ranging from visual discomfort, fatigue and decreased visual performance to the onset of some forms of epileptic seizures.
Flicker characteristics can be found in many commercially available LED sources especially when paired with existing lighting control systems in a retrofit situation. LED flicker mainly depends on the LED driver, and dimming an LED can induce or increase flicker. In general, flicker can be minimised by ensuring supply stability or by using high-frequency electronic control gear that produces a reduced percentage modulation in light output.
Point light sources are less likely to induce seizures and headaches than a diffuse light source. Hence flicker from LEDs used for general lighting such as LED panels appears to have more negative effects than small LEDs used in instrument panels. Moreover, impacts from invisible flicker tend to be stronger for visual tasks requiring precise positioning of eyes, such as when reading.
Night-time exposure to LED lighting
Light has a powerful entrainment effect on human circadian rhythms. When circadian rhythms are synchronised with the solar day, they cause alertness during the day and sleepiness during the night. When they are desynchronised due to factors such as artificial light at night, alertness and sleepiness may occur at the wrong times. If the light experienced at night is brighter, it will have more impact on the body clock, which is designed to respond to light from the sun. Any type of light can do this though the blue light content of some LEDs can mean they have more effect on the body clock.
The light level in the evenings before bed time is important to sleep quality. It can affect the body’s level of melatonin, the hormone that causes sleepiness. If a light source generates a lot of its light in the blue wavelengths, between 400 and 500 nm, this will have a greater potential to suppress melatonin and keep us awake.
A common type of cool white LED chip, which comprises a blue light with a yellow phosphor coating, produces significant light output in the 460 to 500 nm range. Therefore, night-time exposure to such LEDs can be disruptive to circadian rhythms, melatonin production and sleep. However, blue light from LED sources during daytime can also be used to correct disrupted sleep and combat desynchronised circadian rhythms or diminished alertness.
LED content of toxic chemicals
LEDs are made from a variety of semiconductor materials that combine gallium, aluminium and indium with arsenic, phosphorus and nitrogen. Life cycle analysis studies found that LED lamps have significantly lower human toxicity potential than incandescent and compact fluorescent lamps. Unlike fluorescent lamps, LEDs do not contain mercury and this makes them safer if lamps are accidentally broken.
Minimising health risks of LED lighting
LEDs are directional by nature and hence can be very bright and glaring light sources. Very bright LEDs may cause retinal damage if viewed directly. Night-time exposure to bright LEDs rich in blue light can also alter the body clock and lead to various health problems. LEDs can exhibit flicker, which can cause headaches, eyestrain or epileptic seizures in some people. On the other hand, LEDs also have benefits, as they do not contain mercury, have lower human toxicity potential, and emit little or no UV.
So that health risks of LED lighting are minimised, lighting designers and building owners and occupiers should consider a number of measures. Glare should be controlled using suitable shielding or using low glare luminaires. Bright light with a high blue content, such as that emitted by high power cold white LEDs, should be prevented from shining directly in patients’ eyes. Suitable drivers and compatible lighting controls should be used to avoid flicker from LEDs, and dimming should be considered to allow lower light levels in the evening. At the end of life, LEDs should be disposed of correctly by following local lamp recycling instructions.
Dr Cosmin Ticleanu WELL AP MSLL leads BRE’s electric lighting work. With over 15 years of research, consultancy and design experience in lighting, Cosmin provides expert advice on energy efficient lighting and visual comfort. This includes site surveys and computer modelling of lighting and optimisation of existing solutions. Cosmin has authored or co-written more than 50 published papers and books on various aspects of lighting.