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.

Lighting Design continue.pdf

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