What are the most common mistakes made by designers? What is the best thing to look out for when building or renovating a dental practice? Is it worthwhile to require certain parameters for the lighting of a visually demanding operation beyond the standard?

The article under this title was first published in StomaTeam magazine No. 2/2014. The interest of dentists in the quality of lighting is evidenced both by the feedback of Czech readers and by the adoption of this article in the English, French or Russian versions of Cosmetic Dentistry (Dental Tribune). Now we bring it to you in an updated form.

The lighting of dental surgeries is governed by the technical standard ČSN EN 12464-1 specifying the minimum lighting of working areas [1], which is made binding by Government Decree No. 361/2007 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 considered 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 most 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 requires an illuminance of the operating field of at least 15 000 lux in an ellipse of 50 × 25 mm (the site of the visual task); however, at a distance of 60 mm from its upper edge, only 1200 lux is allowed 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 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, to which the peripheral vision is more sensitive and thus a reduction in perceived contrast is achieved. The standard requires light with a high general colour rendering index_Ra > 90. Patients who are forced to look into the luminaire tolerate matt illuminated surfaces best.

The model surgery has dimensions of 5 × 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.

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 must be 500 lx, which is not an ideal value but an ergonomic minimum.

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.

The meaning of the colours in Figures 1 and 2:
" office equipment
" luminaires
" visual task areas
" task surroundings
░ the background of the tasks is the whole surgery

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

Table 2: Comparison and evaluation of the most basic lighting parameters.

Beyond the standard

Although not required by the standard [1], it is desirable that the lighting environment throughout the workplace is homogeneous, which implies the use of a uniform type of light sources (fluorescent lamps or light-emitting diodes) that are spectrally as consistent as possible with natural daylight. The combination of different types and tones of light (halogen bulb, different types of fluorescent lamps, different LED strips) is unnatural to the eye because it requires constant chromatic readaptation.

Measurements taken 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. 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. Moreover, the need for light increases with age.

Other, equally important, lighting parameters include uniformity, glare index, colour rendering, non-visual effects of light or light scattering.

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. Government Decree No. 361/2007 Coll. Government Decree laying down conditions for occupational health protection, as amended.
3. ČSN EN ISO 9680:2015 Dentistry - Dental work lights.

Author. Antonín Fuksa, NASLI, Bc. Filip Svoboda, DentaSun
Published in Stomateam 1/2018