Lighting is essential for healthy and pleasant working conditions in a cleanroom
Cleanroom lighting is important the choice has great influence on healthy and pleasant working conditions. Making the right choice requires some knowledge. Clients have requirements for lighting in cleanrooms and determine them based on what is common in their production process. Strengths between 800 – 1200 lux at worktop level are commonly used in cleanrooms.
Lighting
The criteria that determine what cleanroom lighting must meet are illuminance, luminance ratios, direction of light, reflection, diffuse reflection, light color and light temperature. Among other things, good lighting prevents fatigue during operations. Nuisance is mostly caused by reflections and too much or too little light. Especially in clean rooms, one wants to avoid the possibility of erroneous observations or actions.
Calculation
Using a software module, we calculate the luminance for each work surface. The program takes into account the color and reflection values of walls, ceilings, the floor surface and the height of the lighting relative to the floor.
Standard Illuminance
For cleanroom lighting, we assume the light intensity on the work surface. According to the Dutch Foundation for Illumination Science (NSvV), an average illuminance when installed should be equal to approximately 2 times the standard illuminance. A certain degree of unevenness of the illuminance across the work surface is taken into account.
10 lx to 200 lx Orientation lighting.
Lighting in rooms that are not used as work areas or are used only briefly and where the visual task is not difficult. In general, additional work lighting will be required locally for reading print or tasks of similar detail.
200 Ix to 800 Ix Working illumination.
Lighting in rooms regularly used as workspaces. Most visual tasks can be performed in this area of illuminance levels. The high levels within this area should be used where there is a direct view of an interior space with higher illuminance levels or in deeper parts of the room from where there is a direct view of the high light levels near the window. Also, combinations of small details and weak contrasts, especially for the benefit of the elderly, may result in the need to select a high level of lighting within this class.
800 Ix to 3000 Ix Special work lighting.
Lighting, applied as local lighting for special tasks. Especially when avoiding or generating effects of glare and/or shadow, which affect the visibility of the task, the local character of the lighting is desirable
Explanation
Illuminance levels lower than 200 lx are suitable for areas in which work is carried out for only part of the working time, corridors, stairwells, storage rooms, etc. For this purpose, a minimum level of 10 lx has been adhered to, which will be necessary from the point of view of safety for general orientation and seeing obstacles. Sufficient lighting is guaranteed if the illuminance at floor level is at least 10 lx.
The choice of illuminance depends on:
- the light level in adjoining rooms: if one has a view of a room with a high light level from the workplace, one prefers a higher light level in one’s own working space. For safety reasons, it is necessary that between adjacent and interconnected rooms, lighting strengths do not differ by more than a factor of 20.
- if windows are present, a higher light level (especially further away from the window) is preferred. This is to slightly reduce the difference in light levels, and to reduce adjustment problems when looking up at the bright window;
- small details, weak contrasts and higher employee age require increased light levels;
Luminance ratios
When the ratio of luminance of surfaces that are equal or consecutive in the visual field is large, adaptation problems (retinal adaptation to more or less light) can occur. This can lead to annoyance and loss of concentration.
A rule of thumb regarding luminance ratios is:
- between the visual task (e.g., “clean room” paper) and the immediate environment (e.g., the work surface), the luminance ratio should preferably not exceed 3.
- between the visual task and the periphery (surfaces in the rest of the room), the luminance ratio should preferably not exceed 10.
When choosing LED lighting, light color and color rendering play a role.
A. Light color: For color, the term color temperature is used (T; unit: Kelvin, K). The color of the light source is associated with warmth. Lamps with a low color temperature are attributed a warm light color, lamps with a high color temperature a cool light color.
Warm T < 3300 K
Neutral 3300 K < T < 5300 K
Cool T > 5300 K
B. Color rendering index (Ra): Is the degree to which colors of surfaces illuminated by a given light source are accurately reproduced. The color rendering index is based on the accuracy with which a set of test colors is reproduced by a light source and the at which it is reproduced by a standard light source. By convention, Ra=100. The higher the index the more reliable the color perception.
In cleanrooms, we mostly use 6500 K
Warm colors
2700 K
2700 K
2700 K
2950 K
3000 K
3000 K
White colors
4200 K
4000 K
3800 K
Cool colors
6200 K
7000 K
5000 K
Terms
Illuminance (E; unit lm/m2, lux, lx)
The amount of incident light expressed per unit area (m2).
Illuminance is expressed in lux (lx).
Luminous flux (Ø unit lumen, lm)
The amount of light emitted per unit time by a light source or absorbed by a surface. 1 lx is 1lm/m2.
Standard illuminance (Es; unit:lx)
The illuminance, which should be present at least on the part of the work surface relevant to the performance of the task during the performance of the task.
Luminous intensity (I, unit candela, cd)
Luminous intensity in a given direction represents the amount of light emitted by the light source or an illuminated surface in a given direction.
Luminance (L; unit cd/m2)
The emission of light by objects.
Luminance ratio
The ratio of two luminances in the field of view.
Contrast (luminance contrast)
The ratio of the luminances of the detail to be observed and its background in the visual task.
Diffuse reflection
Diffuse reflection occurs when striking light is scattered in many directions.
Reflectance factor
The ratio of the luminous flux reflected from the surface to the incident luminous flux.
Color rendering
A general expression for the rendering of surface colors when illuminated with light from a particular light source. “Good color rendering” means that the display of colors matches that under an acceptable light source, such as daylight.