Brief Lighting Theory
Just as the design of a hammer handle or pair of pliers is crucial in determining how many hours your body can work before getting tired, the characteristics and direction of your lighting determine how long your eyes can keep working comfortably.
Poor lighting can cause eye dryness, headache and concentration problems. People often automatically adapt to inadequate lighting by changing their body position. Over time, this can cause problems such as repetitive strain injuries, in turn resulting in sick leave.
Sunnex's lighting guide is designed to help you understand the importance of choosing the right lighting.
Light for physicist
What we call light is a form of energy that radiates from a light source, for example the sun or a light bulb. Physicists define light as electromagnetic waves of varying lengths. In everyday language, visible light is defined as radiation which falls within a wavelength range of 380-780 nanometers. The different wavelengths of the radiation represent different colours. It is these colours that we see in a rainbow, or when the light is broken up in a prism.
An object's surface structure reflects certain wavelengths and absorbs others. Together, the reflected wavelengths create the colours we perceive when we look at an object.
Vision takes place in the brain
It is when the light radiation affects the nerve cells in the retina that our picture of our surroundings is created - in the brain. In order for this to happen, light must penetrate the lens of the eye and collect on the retina.
A muscle in your eye changes the shape of the lens to achieve the correct focus. This muscle becomes less efficient with advancing age. People over 40 compensate for this with reading glasses and better lighting. The eye lens is completely transparent when a person is born, but becomes cloudy with age. This is another reason why older eyes need better light than younger eyes. Moreover, the cloudiness causes the light to spread inside the eye, resulting in increased sensitivity to glare.
The pupil is the opening through which light enters the eye. The pupil dilates in dim lighting conditions and contracts in bright lighting. The pupil also contracts at short viewing distances. This means that more light is required for short-range work.
Our retina is made up of cones and rods. The cones enable us to see colour, and are located most densely in the yellow spot. The rods are highly sensitive to light, and help us see in dim lighting. They register different shades of grey between black and white.
Older people are more sensitive to glare than younger people. In addition, older eyes have more difficulty adapting to changes in lighting conditions. For this reason, it is important to be able to adjust the brightness of lighting directed at instruments etc. when working in the dark.
Good lighting is a worthwhile investment
New workstations are often designed on the basis of technical factors alone, while ergonomic factors are ignored. Research shows that good lighting ergonomics are a worthwhile investment in most cases. In order to achieve good production results, it is important to plan the lighting at an early stage of the design project. Good lighting can usually be achieved through simple means.
Precision work and work on moving objects requires bright, correctly directed light, but excessively bright or wrongly directed light causes glare and contrast problems. Glare invariably impairs work performance. There are three types of glare: direct glare, reflective glare and contrast glare.
- Direct glare
The light source must never point straight at the eyes. If the actual light source is visible, direct glare occurs.
- Reflective glare
Reflective glare happens when light from a light source is reflected on a surface within a person's range of vision.
- Contrast glare
This type of glare occurs when there is excessive contrast within the person's range of vision.A good rule of thumb is that the luminance in the inner field of vision, where the object is located, should be three times higher than in the object's surrounding area, which in turn should be three times higher than in the peripheral field of vision. When the eyes move between surfaces with a luminance ratio of 1:5, vision is reduced to the same extent as when a light's brightness is reduced from 1,000 to 30 lux. The eye's ability to adapt is reduced, leading to premature eye fatigue.
Correct colour rendering
The light's composition is vital for correct colour rendering (the way colours are reproduced on the retina). Daylight conditions produce what we perceive as natural colours. Colour rendering is also very good with compact fluorescent tubes and halogen light bulbs. In particular, halogen light bulbs are used in situations where extremely accurate colour rendering is required.
The light strength must always be adapted to the work being performed. Two different workstations cannot be assumed to have the same lighting requirements. For example, a person adjusting a turning tool on a lathe requires a brightness of 3,000 lux, whereas ordinary office work only requires 1,000 lux. A 60W light bulb emits 600 lux at a distance of 40 cm.
The lighting used to illuminate an individual workstation or work task must always harmonise with the general lighting in the room. On the other hand, the general lighting can never replace the lighting needed for an individual task or workstation. If well-designed individual lighting is used in the workplace, the need for strong, dominant general lighting is reduced. This gives the room a more pleasant atmosphere and allows less power to be installed.
Correctly designed workstation lighting has positive effects on employees, work performance, error frequency and energy consumption - all important factors at any workplace. As you can see, meeting the basic requirements for workplace lighting can pay off in many ways.