Lighting Design - Theory and Calculations

LIGHTING DESIGN - ESSENTIALS
TYPES OF LAMPS, NECESSITY OF LIGHTING DESIGN, BASIC
TERMINOLOGIES OF LIGHTING AND DESIGN CALCULATIONS

INCANDESCENT LAMP
• Light is generated by heating a filament with temperature of 2700
K to 2800 K.
• It emits most of it’s energy in the form of infrared radiation or heat.
• Only 5% of energy is converted into visible radiation or light.
• This is one of the main reasons why incandescent lamps are
inefficient in terms of the light emitted and energy that is
consumed.
• As the filament of an incandescent lamp must have very high
temperature in order to give off light, the material of the filament
evaporates relatively quickly.
• It have short lifespan up to 1000 hours.

HALOGEN INCANDESCENT LAMP
• Temperature of the filament is increased to 3000 K.
• The filament material or tungsten gets evaporated
• Later chemically it reacts with the halogen in such a manner that
an important part of the evaporated filament material returns to
the filament.
• This process is known as halogen cycle.
• Hence, due to this process, the lifetime of this lamp is having
longer lifespan than that of normal incandescent lamp up to 2000
- 4000 hours.

FLUORESCENT LAMP
• It consists to have a lamp, the ballast, the luminaire to hold all
of the parts and pieces.
• It has life span of 7,000 – 15,000 hours.
• 60cm lamps are rated to be 18W and 120cm lamps are rated as
36W.
• This happens to be half coated. The bottom half is clear
whereas the upper half is coated with phosphorous.
• Blue emission can be observed – electrical arc stream.
• This excites the gases in the mercury to a higher energy state
so that they can cause phosphorous to glow and hence create
visible light.

COMPACT FLUORESCENT
LAMP(CFL)
• Designed as a replacement for incandescent or halogen
lamps.
• Lifespan: 8,000 – 10,000 hours.
• Recently designed CFLs produce more light per watt,
warms up more quickly, has better light quality, and is
inexpensive.
• CFLs and normal fluorescent lamps function in the same
manner only difference is their shape and size.
• Used for both commercial and residential purpose.

LIGHT EMITTING DIODE(LED)
LAMP
• It is the most efficient source of light.
• Lifespan is up to 50,000 hours.
• It has high power factor about 0.92 and emits high amount
of heat.
• 18W of fluorescent is equivalent to 9W of LED lamp.
• 36W of fluorescent is equivalent to 18W of LED lamp.
• Nowadays, almost everywhere whether it is for commercial,
industrial or domestic purpose, it is replacing fluorescent
blubs.

• They are small point light sources that can be used
individually or in a cluster of more than one chip.
• Optical materials can be used around LED chip or cluster to
direct and screen light.
• If the LED chip or cluster with it’s driver is encapsulated in a
bulb with a conventional lamp foot, they are known as LED
retrofit lamps which can be used as direct replacement of
incandescent lamps.
• Spectral power distribution characterizes light by giving the
power of light at each wavelength in the visible spectrum.

Surface mounted Suspended mounted Wall mounted
Recessed mountedDownlight mounted

WHY LIGHTING
DESIGN IS IMPORTANT?

• Under lighting arrangement in the room will cause
decline in efficiency of the task for which lightings are
designed.
• Over lighting arrangement can cause unnecessary
expenditure.

CONSIDERATIONS IN PRACTICAL
• Lumen output will not be constant in its full lifespan.
• Deposition of the dust on lamps will also cause to reduce output of the
lights.
• Based on the paintings of the room, the lighting design is required to be
different.
• No. of factors that depends on lighting design explained in the upcoming
slides.

LUMINOUS FLUX
• It is the quantity of light emitted by a light source per unit
time(second).
• It is measured in lumens and is represented by symbol - Φ. Unit
– 𝑙𝑚.
• It specifies total amount of light emitted by a lamp.
• Often found in datasheets and specifications of the lamps.
• It does not specify at which direction(s) the light is rated.
• According to IEC, it is measured when lamp operates under
standard condition.

LUMINOUS EFFICACY
• It is the ratio between the luminous flux of a lamp and power
consumed in lamp.
• It is actually the measure of how energy-efficient light can be
produced.
• Formula:
𝐾 =
Φ
𝑃
• Represented by symbol - 𝐾. Unit – 𝑙𝑚/𝑊.
• Higher the lamp efficacy, greater energy efficient the lamp
source.

• CFL lamp has the highest luminous
efficacy in contrast to incandescent and
LED lamps.
• Hence CFL lamp is more energy efficient
compared to incandescent and LED lamps.

LUMINOUS INTENSITY
• It is the quantity of light emitted per second in
specified direction from a point source.
• It is measured in candela. Unit – 𝑐𝑑.
• It is also the luminous flux in a specified
direction radiated per unit of solid angle
omega(𝜔).
• A solid angle can be best described as the
opening angle of a cone.
• Therefore, intensity is the luminous flux
contained in an infinitely small cone divided by
the solid angle of that cone.

ILLUMINANCE
• It is the number of lumens or luminous flux
falling on the surface per unit square area. It is
represented by equation:
𝐸 =
Φ
𝐴
• E – Illuminance, Φ – luminous flux, and A – area
at which light will fall over.
• Unit – lux.
• Examples shown in the next slide.

Summer at noon under a clear sky – 100,000
lux
Heavy cloudy day – 5,000 lux
Office Artificial light – 500 lux Full moon clear night – 0.25 lux

LUMINANCE
• It is the measure of the luminous intensity
emitted per unit area of that surface in a
specific direction.
• It describes the amount of light that passes
through or is emitted from a particular area.
• Unit - candela per square metre (
𝑐𝑑
𝑚2).
• Examples shown in the next slides.

Luminance of the sun – 1,650,000,000
𝑐𝑑
𝑚2 Filament of incandescent lamp– 7,000,000
𝑐𝑑
𝑚2
Fluorescent lamp– 5,000,000 – 15,000,000
𝑐𝑑
𝑚2
Road surface under artificial lighting 0.5 − 2
𝑐𝑑
𝑚2

ILLUMINANCE AND LUMINANCE
RELATIONSHIP
• In the case of light emitting surface, the luminous intensity that the surface emits
is usually not known. But very often, the illuminance on the surfaces is.
• Illuminance is independent of the type of surface. It doesn’t matter if it’s a wall,
desk or table top. It only depends on the amount of light falling on that surface.
• For perfectly diffusing surface, a relationship exists between the illuminance on
the surface, the surface reflectance and the luminance of the surface.
• Reflectance refers to the fraction of incident light that is reflected from a surface.

ROOM INDEX (R.I.)
• It is based on share and size of room that describes room’s
length, width and height.
• Range: 0.75 – 5m.
• It is represented by formula:
𝑅. 𝐼. =
𝑙 × 𝑤
ℎ 𝑤𝑐(𝑙 + 𝑤)
• 𝑙 – length of the room, 𝑤 – width of the room, ℎ 𝑤𝑐 – height
between work plane i.e. bench to ceiling.
• It is applicable when 𝑙 < 4𝑤.

MAINTENANCE FACTOR (M.F.)
• It is also known as the light loss factor.
• It is the ratio of the lamp lumen output after a period of time
to lamp lumen output when it was new. Represented by
formula:
𝑀. 𝐹. =
𝐿𝑎𝑚𝑝 𝑙𝑢𝑚𝑒𝑛 𝑜𝑢𝑡𝑝𝑢𝑡 𝑎𝑓𝑡𝑒𝑟 𝑝𝑒𝑟𝑖𝑜𝑑 𝑜𝑓 𝑡𝑖𝑚𝑒
𝐿𝑎𝑚𝑝 𝑙𝑢𝑚𝑒𝑛 𝑜𝑢𝑡𝑝𝑢𝑡 𝑤ℎ𝑒𝑛 𝑖𝑡 𝑤𝑎𝑠 𝑛𝑒𝑤
• It is always less than 1.
• Typical values:
• For offices and classrooms – 0.8
• For clean industry – 0.7
• For dirty industry – 0.6

UTILIZATION FACTOR (U.F.)
• It is the measure of how effective the lighting scheme is.
Represented by the formula:
𝑈. 𝐹. =
𝐿𝑢𝑚𝑖𝑛𝑜𝑢𝑠 𝑓𝑙𝑢𝑥 𝑓𝑎𝑙𝑙𝑖𝑛𝑔 𝑜𝑛 𝑝𝑙𝑎𝑐𝑒 𝑜𝑓 𝑠𝑢𝑟𝑓𝑎𝑐𝑒
𝐿𝑢𝑚𝑖𝑛𝑜𝑢𝑠 𝑓𝑙𝑢𝑥 𝑔𝑖𝑣𝑒𝑛 𝑜𝑢𝑡 𝑏𝑦 𝑡ℎ𝑒 𝑙𝑎𝑚𝑝
• It is dependant on:
• Efficiency of luminaire.
• Distribution of luminaire.
• Reflectance of Room.
• Geometry of the space.
• Polar curve.

ROOM’S REFLECTION
• Three main surfaces:
1. Floor
2. Walls
3. Ceiling
• Light colours such as white and yellow will have more
reflectance in contrast to dark colours such as blue and
brown.

SPACE TO HEIGHT RATIO
• It is the ratio of distance between adjacent luminaires(centre
– centre) to their height above working plane. Formula:
𝑆𝐻𝑅 =
1
𝐻 𝑚
𝐴
𝑁
where 𝐻 𝑚 - Mounting height, A – Total area of the floor and N –
Number of luminaires
• It should not exceed maximum value of SHR of luminaire as
provided by the manufacturer.

LIGHTING DESIGN
CALCULATION - STEPS

1. Depending for which type of room lighting design to be done, find the value of lux from
IES Room Illumination level sheet -
http://www.pioneerlighting.com/new/pdfs/IESLuxLevel.pdf.
2. Select suitable efficient luminaire.
3. Compute Room Index.
4. Check Utilization Factor table (next slide).
5. Computer number of luminaires which is given by the formula:
𝑁 =
𝐸 × 𝐴
𝐹 × 𝑛 × 𝑈. 𝐹.× 𝑀. 𝐹.
where N – Number of luminaires, E – Illuminance level (𝑙𝑢𝑥), A – Area at working plane (𝑚2
),
F – Average luminous flux from each lamp (𝑙𝑚) , n – Number of lamps in a luminaire

UTILIZATION FACTOR TABLE
• It is provided by the manufacturer of the
luminaires
• Room Reflection coefficients: C – Ceiling, W –
Wall reflection and F – Floor reflection
• E.g. if Room Index = 1.5 of a room and reflection
coefficients are C = 0.70, W = 0.3 and F = 0.2,
Utilization factor = 0.54
• This table can differ slightly from one
manufacturer to another.

6. Determine minimum spacing between luminaires. Formula:
𝑀𝑖𝑛𝑖𝑚𝑢𝑚 𝑠𝑝𝑎𝑐𝑖𝑛𝑔 = 𝑆𝐻𝑅 × 𝐻 𝑚
7. Determine number of required rows of luminaire along width of the room. Formula:
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑟𝑒𝑞𝑢𝑖𝑟𝑒𝑑 𝑟𝑜𝑤𝑠 =
𝑊𝑖𝑑𝑡ℎ 𝑜𝑓 𝑡ℎ𝑒 𝑟𝑜𝑜𝑚
𝑀𝑖𝑛𝑖𝑚𝑢𝑚 𝑠𝑝𝑎𝑐𝑖𝑛𝑔
8. Determine the number of luminaires in each row. Formula:
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑙𝑢𝑚𝑖𝑛𝑎𝑖𝑟𝑒𝑠 𝑖𝑛 𝑒𝑎𝑐ℎ 𝑟𝑜𝑤 =
𝑁𝑜. 𝑜𝑓 𝑙𝑢𝑚𝑖𝑛𝑎𝑖𝑟𝑒𝑠
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑟𝑜𝑤𝑠
9. Determine axial space between each luminaire. Formula
𝐴𝑥𝑖𝑎𝑙 𝑠𝑝𝑎𝑐𝑒 =
𝐿𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑡ℎ𝑒 𝑟𝑜𝑜𝑚
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑙𝑢𝑚𝑖𝑛𝑎𝑖𝑟𝑒𝑠 𝑖𝑛 𝑒𝑎𝑐ℎ 𝑟𝑜𝑤

10. Determine the transverse space between luminaires. Formula:
𝑇𝑟𝑎𝑛𝑠𝑣𝑒𝑟𝑠𝑒 𝑠𝑝𝑎𝑐𝑒 =
𝑊𝑖𝑑𝑡ℎ 𝑜𝑓 𝑡ℎ𝑒 𝑟𝑜𝑜𝑚
𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑟𝑜𝑤𝑠
11. Determine the distance between luminaire and wall. Formula:
𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 𝑙𝑢𝑚𝑖𝑛𝑎𝑖𝑟𝑒 𝑎𝑛𝑑 𝑤𝑎𝑙𝑙 =
𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 2 𝑎𝑑𝑗𝑎𝑐𝑒𝑛𝑡 𝑙𝑢𝑚𝑖𝑛𝑎𝑖𝑟𝑒𝑠
2
Note: All the distances between luminaires either axial, transverse and distance between
luminaire and wall (vertical as well as horizontal) are distanced from the centre position of
the luminaire(s).

LIGHTING DESIGN CALCULATION -
CLASSROOM EXAMPLE

SPECIFICATIONS
Note: Please refer to the steps in previous while attempting to solve this
problem on your own or going through the solution of this problem.

1. Value of lux for classroom – 300 lux.
2. Luminaire – 40W Philips BN208C LED Lamp.
3. From ceiling to study table, height = 2 m. Therefore ℎ 𝑤𝑐 = 2 𝑚
𝑅𝑜𝑜𝑚 𝐼𝑛𝑑𝑒𝑥 =
6 × 9
2 × (6 + 9)
= 1.8
4. Determining U.F. from U.F. table and as per the specification as follows:
Therefore, 𝑈. 𝐹. = 0.65 as 𝑅𝑜𝑜𝑚 𝐼𝑛𝑑𝑒𝑥 = 1.8 ≈ 2

5. From LED Batten Philips datasheet: 𝐹 = 3892 𝑙𝑚 and Number of lamps in
luminaire 𝑛 = 1. 𝑙 = 6 𝑚, 𝑤 = 9 𝑚, 𝑈. 𝐹. = 0.65 and 𝑀. 𝐹. = 0.8. Therefore
Number of luminaires:
𝑁 =
300 × 6 × 9
3892 × 1 × 0.65 × 0.8
= 8
6. 𝑀𝑖𝑛𝑖𝑚𝑢𝑚 𝑠𝑝𝑎𝑐𝑖𝑛𝑔 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 𝑙𝑢𝑚𝑖𝑛𝑎𝑖𝑟𝑒𝑠 =
1
𝐻 𝑚
𝐴
𝑁
× 𝐻 𝑚 =
6×9
8
= 2.6 𝑚
7. 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑟𝑒𝑞𝑢𝑖𝑟𝑒𝑑 𝑟𝑜𝑤𝑠 =
9
2.6
= 3.46 ≈ 4
8. 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑙𝑢𝑚𝑖𝑛𝑎𝑖𝑟𝑒𝑠 𝑖𝑛 𝑒𝑎𝑐ℎ 𝑟𝑜𝑤 = 8/4 = 2
9. 𝐴𝑥𝑖𝑎𝑙 𝑠𝑝𝑎𝑐𝑖𝑛𝑔 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 𝑙𝑢𝑚𝑖𝑛𝑎𝑖𝑟𝑒𝑠 =
6
2
= 3 𝑚

10. 𝑇𝑟𝑎𝑛𝑠𝑣𝑒𝑟𝑠𝑒 𝑠𝑝𝑎𝑐𝑖𝑛𝑔 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 𝑙𝑢𝑚𝑖𝑛𝑎𝑖𝑟𝑒𝑠 =
9
4
= 2.25 𝑚.
11. Distance between luminaire and wall:
𝑉𝑒𝑟𝑡𝑖𝑐𝑎𝑙 =
3
2
= 1.5 𝑚 and
𝐻𝑜𝑟𝑖𝑧𝑜𝑛𝑡𝑎𝑙 =
2.25
2
= 1.125 𝑚.
Note: Labelled details of the diagram
represented in the next slide.

Lighting Design - Theory and Calculations

Bulbs.com. 2018. Compact Fluorescent | Light Bulb Types | Bulbs.com .
[ONLINE] Available at: https://www.bulbs.com/learning/cfl.aspx. [Accessed 06
February 2018].
Electrical Technology. 2018. Lighting Design Calculation in a Building - Electrical
Wiring Installation. [ONLINE] Available
at: https://www.electricaltechnology.org/2017/03/lighting-design-calculation-in-
building.html. [Accessed 06 February 2018].
Hasan Tariq. 2018. LIGHTING DESIGN BY LUMEN METHOD( WITH
EXAMPLES). [ONLINE] Available at: https://www.linkedin.com/pulse/lighting-
design-lumen-method-examples-hasan-tariq/. [Accessed 6 February 2018].
YouTube. 2018. Philips Lighting University (short video nuggets) - YouTube.
[ONLINE] Available
at: https://www.youtube.com/playlist?list=PLj9hU1O4UB02hL7ABUsWNIZ-
PVBoONl9N. [Accessed 06 February 2018].
Udemy. 2018. Electrical Power Distribution with AUTOCAD, DiaLux & Etap |
Udemy. [ONLINE] Available at: https://www.udemy.com/electrical-power-
distribution-with-autocad-dialux-etap/learn/v4/. [Accessed 06 February 2018].

Lighting Design - Theory and Calculations

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