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We take in more than 80% of information by sight, so proper lighting plays a vital role in virtually all human activities. In healthcare, the most noble values such as human health and life are at stake.
The lighting of dental surgeries is governed by a technical standard [1], which is made binding by law [2]. The current standard has been in force since 2012 and some lighting systems designed according to the previous standard from 2004 are no longer compliant. The requirements of the standard should be taken as a hygiene minimum. The requirements of the standards are a compromise between average physiological needs and average economic possibilities. According to ergonomic research, people in the office mostly prefer 2000 lx illuminance, whereas the standard prescribes a minimum of 500 lx.
The standard specifies a maintained illuminance of Ēm. If the actual illuminance E falls below Ēm, the system must be maintained: cleaning of luminaires, replacement of light sources, painting, etc.
Adequate illumination of the operating field is essential for visual performance. The standard [3] for operating theatre lamps specifies an illuminance of the operating field controllable at least in the range of 8000-20000 lx in an ellipse of 50 x 25 mm(the site of the visual task); however, only 1200 lx is allowed at a distance of 60 mm upwards from the centre of the ellipse so as not to dazzle the patient.
The constant readaptation of the eye between very bright and dark areas leads to visual and eventually overall fatigue. A powerful luminaire suspended above the chair is helpful here, providing - and often exceeding several times over - the required minimum maintained patient illuminance of 1000 lx (corresponding to the immediate task surroundings - a strip at least 0.5 m wide around the visual task area). Less contrast means better visual comfort for the clinician. Preferably, cool tones of white light are used here, as they contain a higher proportion of the blue component, to which peripheral vision is more sensitive, and thus a reduction in perceived contrast is achieved. The standard calls for light with a high general colour rendering indexRa > 90.
In addition to the visual task in the oral cavity, there are a number of other places in the office: instrumentation table, controls and displays of diagnostic instruments, preparation of materials, computer table, filing cabinet and more. In all these areas, the required lighting for the activities must also be met. At the same time, the minimum total illuminance of the surgery of 500 lx must be met.
One of the major innovations in the revised standard is the task background, which is an area adjacent to the immediate surroundings of the task, at least 3 m wide within the boundaries of the space. According to the standard, this should be illuminated by at least 1/3 of the actual illuminance of the immediate task surroundings. This is also where the most common mistakes in lighting design according to the old standard occur. Under a powerful pendant luminaire with a weak indirect component we can easily measure patient illuminance up to 5000 lx. The task background, which makes up most of the room, should be illuminated at 1670 lx in this case, which is quite expensive to achieve. This ratio was not met in any of the dozens of practices measured where a powerful pendant luminaire was placed above the set. The standard here forces us to consider the surgery as a whole, where not only patient illuminance matters, but also uniformity and acceptable contrast throughout the space. Too high a luminaire wattage will therefore disturb the uniformity of the lighting - see Figures 1 and 2.
Measurements taken in surgeries show that task lighting and general illumination are often inadequate, with all the consequences of visual fatigue. The 150 lx at the materials preparation area or at the computer desk is no exception. Failure to follow the maintenance schedule is also common. Many offices in older buildings do not have lighting installed entirely according to design, and old luminaires designed according to a very old standard that required only 300 lx in offices are still in place.
It really pays not to skimp on lighting. Savings can be found, for example, in lighting control. Moreover, the need for light increases with age. Not to see can mean to forget.
In a future article we will discuss other lighting parameters such as uniformity, glare index, colour rendering, non-visual effects of light and lighting control.
| Fig. 1: A typical situation in a surgery where lighting is provided only by a powerful directional luminaire above the chair. Most of the requirements are not met, see Table 2. | Fig. 2: Balanced lighting of the surgery with a less directional luminaire above the chair and additional ceiling and sub-line luminaires, see Table 2. |
" equipment of the surgery " luminaires " places of visual tasks " surroundings of the tasks ░ the background of the tasks is the whole surgery
| It should be noted that in neither case is the main luminaire sufficient to meet all the illuminance conditions. Therefore, additional luminaires are necessary to guarantee correct background illumination and sufficient uniformity. In the case of Figure 2, achieving the required values is economically less demanding. |
| Parameter | Fig. 1 | Fig. 2 |
| General lighting of the surgery | 20-2000 lx | 600-1500 lx |
| Uniformity overall | unsatisfactory | very good |
| Patient lighting | 2000-5000 lx | 1000-3000 lx |
| Instrument lighting | 100-200 lx | 500-700 lx |
| Illumination of material preparation | 30-300 lx | 500-750 lx |
| Nurse's table lighting | 50-300 lx | 500-750 lx |
| Doctor's table lighting | 20-100 lx | 700-800 lx |
| Backlighting | 20-1000 lx | 600-1000 lx |
| General colour rendering index | 80-89 | > 90 |
| Compliance with the standard | NO | YES |
Table 1: Comparison and evaluation of the most basic lighting parameters.
The model surgery has dimensions of 5 x 6 m and a ceiling height of 2.8 m. The luminaire above the chair is suspended at a height of 2.2 m. The arrangement of the additional luminaires is a compromise between functionality and aesthetics.
| Fig. 3: 3D visualisation of the situation in Figure 1. The lighting does not respect other visual tasks in the office. | Fig. 4: 3D visualisation of the situation in Figure 2. . View of the model surgery with luminaires respecting other visual tasks |
| Symbol | Meaning of Purpose | General lighting surgery | Patient lighting |
| Em | Maintained illuminance Adequate lighting levels. | 500 lx | 1000 lx |
| UGRL | Glare index limit UGR Glare avoidance, acceptable contrast. | 19 | - |
| Oo | Minimum lighting uniformity Acceptable light distribution in the space. | 0,6 | 0,7 |
| Ra | Minimum General Colour Rendering Index Required colour resolution. | 90 | 90 |
| - | Specific requirements For the selected location or activity. | Light should not dazzle the patient | - |
Table 1 - Lighting requirements for dental practices (according to Table 5.48 of the standard [1])
Literature:
[1] EN 12464-1:2012 Light and lighting - Lighting of work areas - Part 1: Indoor work areas.
[2] Act 361/2007 Coll. Government Regulation laying down conditions for occupational health protection, as amended.
[3] EN ISO 9680:2007 and 2015 Dentistry - Dental work lights.
Author. Antonín Fuksa, NASLI, Bc. Filip Svoboda, DentaSun
Published in StomaTeam 2/2014
