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 the technical standard ČSN EN 12464-1 specifying the minimum lighting of work areas,[1] which is made binding by Act No. 61/2007 Coll.[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 hygienic minimum. The requirements of the standards are a compromise between average physiological needs and average economic possibilities. According to ergonomic research, people in the workplace mostly prefer a total illuminance (outside the operating field and its immediate surroundings) of at least around 1000 lx, whereas the standard prescribes a minimum of 500 lx. The standard specifies a maintained illuminance of Ēm (the value of the average illuminance on a given surface below which the illuminance must not fall). If the actual illuminance E falls below Ēm, the system must be maintained: cleaning of luminaires, replacement of lamps, painting, etc.

Adequate illumination of the operating field is essential for visual performance. The standard [3] for operating theatre lamps on the set specifies an illuminance of the operating field controllable at least in the range of 8000-20000 lux in an ellipse of 50 × 25 mm (the site of the visual task); however, only 1200 lux is allowed at a distance of 60 mm upwards from its centre so as not to dazzle the patient. The constant readaptation of the eye between very bright and dark areas leads to visual and eventually general fatigue.

The aid here is a powerful luminaire suspended above the chair that provides - and often exceeds several times over - the required minimum maintained patient illuminance of 1000 lx (corresponding to the immediate surroundings of the visual task - a strip at least 0.5 m wide around the visual task area). Less contrast means better visual comfort for the doctor. 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 index Ra > 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.

@obr1@
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 1.

@obr1@
Fig. 2: Balanced office lighting with a less directional luminaire above the chair and additional ceiling and sub-line luminaires, see Table 1.

■ office equipment ■ luminaires ■ visual task locations ■ task surroundings The background of the tasks is the whole office
Note: the numerical values indicate the illuminance in lux

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.

Measurements carried out in surgeries show that task lighting and general illumination are often inadequate, with all the consequences of visual fatigue. Even as little as 150 lx at the materials preparation area or computer desk is no exception. Failure to follow the maintenance schedule is also common.

A number of surgeries established in older buildings do not have lighting installed completely according to the project, the old luminaires designed according to a very old standard that required only 300 lx in offices remain. It really pays not to skimp on lighting. Moreover, the need for light increases with age.

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. 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.

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 Dentistry - Dental work lights.

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.

Table 2: Lighting requirements for dental practices (according to Table 5.48 of the standard) [1]

Author. Antonín Fuksa
Published in StomaTeam magazine