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British Standards BS 161 (IEC 64)
Domestic gls lamps (1000 hours).
BS 6179 GLS lamps (2000 hours).
Colour Rendering
Colour rendition defines how the light from a lamp affects the colour appearance of objects
being illuminated. It will therefore vary in practice depending on the colours of the actual
objects. However, a generalised approach is that good colour rendering means the accurate rendition
of all colours.
Incandescent lamps have good colour rendering and people are accustomed to seeing objects
under incandescent illumination. However, incandescent light is biased towards the red end of the
spectrum, so is considered to create a "warm" appearance.
Incandescent lamps have a general colour rendering index (CRI or Ra) of 100. The colour
rendering scale is from 0 to 100. The topic of colour performance is covered in fuller detail in a
later lesson.
Incandescent Lamp Advantages
Incandescent lamps offer a number of advantages:
-
Simple to use - direct connection
into socket.
-
Lowest initial lamp cost.
-
Immediate starting and re-starting
- no warm-up or cool down required.
-
Excellent optical control -
concentrated light source is easiest to direct or focus.
-
Easiest to dim - simple variable
resistor circuitry may be all that is required.
-
Wide design flexibility - variety
of styles, outputs, and colours fill nearly every need.
-
Output not affected by operation
over a wide range of ambient temperature.
-
Available in wattage ratings from
10 to 100W.
Incandescent Lamp Disadvantages
-
Sensitive to shock and vibration -
use ROUGH or VIBRATION SERVICE lamps or special sockets in high shock or vibration
environments.
-
High overall operating cost - low
efficacy and short life.
-
Sensitive to voltage variations.
See figure 4.17.
Operating 240V lamp on 226V (-6%)
reduces wattage by 10%, reduces light output by 20% and increases lamp life by 30%.
Operating 240V lamp on 254V (+6%) increases wattage by 10%,increases light output by 22% and
decreases lamp life by 30%
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