With indirect (in-built) lighting, the lighting is built into the instrument. The advantages are:
1. The light does not spread to other areas.
2. The lighting can be tailor-made for each individual instrument.
3. The light fitting or lamp does not block anything in the workplace.
The disadvantages are:
1. The area between the instruments is not illuminated, which may make an instrument look as though it is ‘floating in midair’.
2. It may be difficult to achieve even lighting over the face of the whole instrument.
The most common in-built lighting systems are:
Indirect lighting—The lighting is placed behind the instrument face, which is made of a material which lets sufficient light through.
Edge lighting—This lighting technique works by manufacturing the instrument out of a material, which normally permits light to pass through. The instrument is then painted completely black, apart from the figures, which are to be read. One advantage for this technique is that different colours can be used for different instruments.
Self-illuminating (fluorescent) markings—Here two techniques can be used: fluorescent or electro-fluorescent. Electro-fluorescent markings have the advantage that they are only illuminated when current is applied. With these techniques, only the markings and the numbers/letters on the instrument are seen. The advantages of these techniques are:
1. Even lighting and colour of the markings
2. Ability to change the colours