lighting design continue.pdf
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EE8236 ELECTRICAL SYSTEMS IN BUILDINGS
Lecture 04
Illuminance - Light Level - Recommended Levels
Recommended light level - illuminance - for different types of working activities.
Light Level or Illuminance, is the amount of light measured in a plane. The work plane is
where the most important tasks in the room or space are performed.
Measuring Units Light Level - Illuminance
Illumenance is measured in foot candles (ftcd, fc) (or lux in the metric SI system). A foot
candle is actually one lumen of light density per square foot, one lux is one lumen per square
meter.
lux = fc 10.752
fc = lux / 10.752
Common Light Levels Outdoor
Common light levels outdoor at day and night can be found in the table below:
Table 2.4.1
Common and Recommended Light Levels Indoor
The outdoor light level is approximately 10,000 lux on a clear day. In the building, in the
area closest to windows, the light level may be reduced to approximately 1,000 lux. In the
middle area its may be as low as 25 - 50 lux. Additional lighting equipment is often necessary
to compensate the low levels.
Earlier it was common with light levels in the range 100 - 300 lux for normal activities.
Today the light level is more common in the range 500 - 1000 lux - depending on activity.For precision and detailed works, the light level may even approach 1500 - 2000 lux.
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The table below is guidance for recommended light level in different work spaces:
Table 2.4.2
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Table 2.4.3
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Lighting Calculations
When performing industrial lighting calculations, many factors can cause the actual
illuminance to vary from the calculated illuminance; for example, incorrect surface
reflectances, not accounting for large machinery and other obstructions that block light, and
inaccurate light loss factors (LLF). Total LLF takes into account that the fixtures will getdirty over time, that lamps will age causing the lumen output to decrease and that ballast
operation plays a factor in lumen output. It is always best for the designer to calculate the
appropriate LLF and to know the exact reflectances in order to get more accurate
illuminance levels; however, the following rules of thumb can be applied for quick
calculations.
Table 2.4.4
*Includes ballast factor. Based on energy saving lamps/energy saving ballast or T8
lamps/electronic ballast
Table 2.4.5
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Thermal Considerations:
Thermal Characteristics of a Fluorescent Lamp:
Fluorescent sources are sensitive to temperature extremes. Optimum light output for most
fluorescent lamps occurs when the bulb wall temperature is 100° F. Any temperature aboveor below optimum reduces light output.
Figure 2.4.4
Fluorescent Ballast Performance:
Table 2.4.6
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Luminous Efficacy
Luminous efficacy is a measure of how well a light source produces visible light. It is
the ratio of luminous flux to power (measured in lm/W). Typical values of luminous
efficacy for different type of lamps are as given in Table 2.4.7.
Table 2.4.7.
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Home Work
Find out the details for following topics.
Circuit of a fluorescent lamp: Magnetic & Electronic
T rating of a fluorescent lamp
Kind of light fittings for fluorescent lamps
Star rating of CFL
LED lamp types applications
Typical accessories for a lighting installation
Types of outdoor light fittings, their IP rating
Other types of interior lighting design
Installation height of a light switch.