AR 4.5 BUILDING SERVICES - II:ELECTRICAL SERVICES:

Unit – V:

Lighting Calculation: NBC standards, nominal illumination levels in building interiors, lux, lumen, intensity, lighting schemes.  

ILLUMINATION AND LUX:What is the method for calculating illumination ?The problem of the Architect / Lighting Designer at the functional level is to determine how many lights and where to place them to get the correct level of illumination for a given activity.What do we understand by LUX ?The lux (symbol: lx) is the SI unit of illuminance and luminous emittance, measuring luminous flux per unit area. It is used in photometry as a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface. It is analogous to the radiometric unit watts per square metre, but with the power at each wavelength weighted according to the luminosity function, a standardized model of human visual brightness perception. In English, "lux" is used in both singular and plural.

ILLUMINATION AND LUX:One lux is equal to one lumen per square metre: 

A lux meter for measuring illuminances in work places.

ILLUMINATION AND LUX:One lux is equal to one lumen per square metre: 

In other words .. LUX = Level of Illumination.

OR

LUX (lx) = Lumens / Sq.M.Level of Illumination ?LUMEN METHOD:This method works perfectly in most cases where the height of the ceiling is within 3000 mm from floor level, the Working Plane is between 750 to 1000 mm and proportions of the area are proper.

ILLUMINATION AND LUX:How To Calculate Lux ?

How do I calculate lux - the formula?

Lux level = total light output (lumens) / area (square meters)

Total Light Output = lumens per fixture * number of fixtures

Therefore

Number of Fixtures = (Lux level * area) / lumens per fixture

ILLUMINATION AND LUX:

Every Lamp has certain Lumens.

You need to look up the manufacturer data for your light fitting to get the lumens per fixture.

S.No.

Type of Lamp. Lumens Output.

1. 36 W Tube Light. 2400 Lumens.

2. 60 W GLS Lamp. 600 Lumens.

3. 10 W CFL. 600 Lumens.

ILLUMINATION AND LUX:Example:Assume a Room size of = 10000 x 8000 x 3000 = 80 Sq.M.Area = 80 Sq.M.

Suppose the desired lux level or Illumination = 300 lx.

Total Lumens required = 300 x 80 = 24,000 lumens.

Assuming that you are using 36W Lamp (FTL) and the same has 2,400 lumens illumination.

Number of Fixtures required = 24,000 / 2400 = 10 Nos.So you need 10 Nos. of 36W Tube Light Fittings.

ILLUMINATION AND LUX:What we did above is still not sufficient as there are certain Correction Factors involved. There are basically two Correction Factors i.e., Utilization Factor = UF and Maintenance Factor = MF.UTILIZATION FACTOR: (UF)

This may be due different reasons viz., Room Reflectance's, Dimensions etc.,

The utilization factor (UF) is a Direct ratio. This is the proportion of the downward luminous flux that reaches the work area directly without reflection. It depends on the shape of the room. The Direct ratio has a low value with a tall narrow room (small RI) and a high value for a wide room (large RI).

ILLUMINATION AND LUX:The light distribution from the luminaries. Luminaries that emit light through a larger solid angle will generally have a smaller direct ratio that luminaries that emit light in a narrower beam.

There exist data sheets of UF for rooms of different shapes and luminaries of a common type.

Catalogues of luminaries often provide data sheets of UF for rooms.

Normally we take 0.8 as the Utilization Factor.

ILLUMINATION AND LUX:This utilization factor is somewhat more complicated to determine than the maintenance factor.

The utilization factor will depend on the following:

The luminarie properties. One needs the light output ratio (LOR). How much of the light emitted by the lamps actually leaves the luminarie? An enclosed lamp in a luminarie with low reflectivity will have a smaller LOR than a naked lamp.

The light emitted downwards will probably reach the work area without reflections. However light emitted upwards can only reach the work area after reflection(s) from surfaces.

ILLUMINATION AND LUX:The utilization factor will depend on the following:The reflectance of the room surfaces. Are the surfaces (walls, ceiling) light or dark in color?(A color with strong chroma does not reflect other colors). Reflectance's are available from manufacturers of paints and furniture finishing's. It is usual to make the reflectance of the ceiling highest, walls slightly lower and the floor darker. Reflectance's of desks should be 20-40%. Do not choose very dark wood, or bright surfaces.The geometric proportion of the room. The geometric shape of the room will affect the UF. A factor called the room index (RI) is defined from the horizontal vertical areas of the room.

ILLUMINATION AND LUX:MAINTENANCE FACTOR: (MF)It is also known as LLF OR Light Loss Factor. This may be due different reasons viz., Time, Temperature, Cleanliness etc.,The maintenance factor gives an estimate of how lighting conditions will deteriorate through use. Some factors are: • Dust and dirt inside luminaries surfaces. • Aging of light bulbs emitting less light. • Cleaning of room surfaces, e.g. ceiling. Normally we take 0.75 to 0.8 as the Maintenance Factor.

ILLUMINATION AND LUX:Coming back to our earlier Example where we said that we need 10 Nos. of 36W Tube Light Fittings.Now with application of UF and MF it will be as follows:

No. of Fixtures = 10 / 0.8 x 0.8 = 15.625 i.e., 16 Nos.

But practically many times to maintain the balance we may use upto 12 Nos. of fixtures also.Formula for Number of Fixtures.

Lux x Area /

300 x 80 /15.625

Lumen Output x MF x UF

2400 x 0.8 x 0.8

LIMITATION OF LUMEN METHOD:There are certain limitations to this method, but all said and done this works perfectly for 90% of the installations where the parameters are within the limits.Height is not considered.Fixtures or luminaries changes are not considered. (Polar curve etc.,)Room Reflectance's are not considered.It does not distinguish between different fixture behaviors i.e., point source or linear source etc.,

For this there is one more complicated method known as POIINT BY POINT METHOD. This is more specific for experts in Lighting Design and detailing.

GLARE:The control of glare:Glare occurs in both natural (daylight) and in interior lighting situations. It is most annoying in the interior light environment where the lighting is under human control.The glare annoyance depends on a number of factors In a supermarket people are on the move and not always looking in same direction.In a classroom students are usually looking in a fixed direction.In a classroom, students are reading, this is a moderately difficult visual task.Students are fixed for a long period of time.Standards for glare depend on the use of the visual environment.

GLARE:

The glare index

There is quantity called the discomfort glare constant (g) which is:

Glare index. Reaction.

0 - 10 Imperceptible

10 - 16 Noticeable

16 - 22 Acceptable

22 – 28 Uncomfortable

> 28 Intolerable

GLARE:More visually demanding tasks with high illuminance levels are less tolerant of glare.

(At present time, do not require you to calculate the glare index, require you to know what it is and when it is most important to eliminate.)

Limiting GI

Occupations

16 Drawing offices, very fine visual inspections.

19 Offices, libraries, keyboard and VDT work (reflections from screen).

22 Kitchen, reception area, fine assembly.

25 Stock rooms, assembly line for easy tasks.

28 Indoor car park, rough industrial work.

GLARE:CONTROL OF GLARE:First of all, glare from all sources is additive and people get annoyed by all sources of discomfort glare.Obviously, cutting down the illuminance of the glare source, Ls is a good idea. This does not mean reducing the light level in the room. The higher the illumination of the background, the smaller the glare constant. So rather than having one very bright luminaire, have a number of dimmer luminaries.Most of the visual tasks involve looking horizontally or slightly down. So keep luminaries out of the low angle vision. So do not gives walls too high a reflectance. Do not give the floors too high reflectance (no glossy light floors!).

GLARE:TIPS TO CONTROL GLARE:Keep luminance of source down. Use of diffusers and louvres. Cutting down glare also cuts down total light emitted and this problem also needs to be tackled. Reflected light can also be a source of glare.Keep luminaires out of field of view. High ceilings are good. Keep area of source small. To cut down glare, avoid luminaires that emit light to sides (e.g. battern luminaire with a diffuser at the sides), light emitted more in downward direction avoids visual discomfort.

GLARE:UPLIGHTING:In this form of lighting, lighting is directed upwards to the ceiling. Reflected light from the ceiling provides the general illumination in the room.Advantages, elimination of glare is one of the major advantages.Re-introduction driven by the increasing use of computers.Disadvantage, it is somewhat inefficient. Low conversion of electrical energy into usable light. If the Ceiling is quite bright, it will have less visual emphasis on other areas of room, furniture, floors.To get an even illumination on the ceiling requires that you have a high ceiling.

GLARE:UPLIGHTING:You either like it or not. It is possible to use combinations of direct diffuse and indirect lighting.Illumination can be calculated using lumen method in conjunction with transfer function tables.Need to maintain a uniform illumination on ceiling.Eliminates light hot-spots that can result in glare.Harder with low ceiling.Besides less glare, concentrated beam downlights result in darker ceiling. This can result in an oppressive psychological effect.

LIGHTING STANDARDS:What are the legal requirements for office lighting? Is there a legal requirement for daylight?The only legal requirements are 'sufficient and suitable' and similar wording in health and safety legislation. There is no absolute legal requirement for daylight, but it is a requirement that it be provided if practicable. Various guidance documents suggest good practice, but are not themselves mandatory.What is the recommended lighting level for offices? The Code for Lighting recommends a maintained illuminance of 500 lux for general offices (e.g. writing, typing, reading, data processing, etc.) and for CAD work stations and conference/meetings rooms. Where the main task is less demanding, e.g. filing, a lower level of 300 lux is recommended.

ILLUMINATION LEVELS AND LIMITING GLARE:

The table following lists illumination levels suitable for a range of situations: the quality of these levels could be influenced by glare and an acceptable limiting index is also shown. The glare index is calculated by considering the light source location, the luminances of the source, the effect of surroundings and the size of the source.

Glare indices for artificial light range from about 10 for a shaded light fitting having low output to about 30 for an un shaded lamp. 

ILLUMINATION LEVELS AND LIMITING GLARE:

As seen from this illustration, various basic decisions have to be made concerning lighting objectives and whether the system involves daylight, electric light or a combined system. With electric or combined systems, further decisions must be taken concerning the way light is distributed by particular fittings, and upon their positions relative to each other as well as in relation to the surface to be illuminated. As with day lighting, light-coloured and highly reflective room surfaces help to provide more illumination from the same amount of  energy source – it preserves the luminance effect of the light source.

ILLUMINATION LEVELS AND LIMITING GLARE:

Location. Illuminance. (lx) Limiting Glare Index.

Entrance Hall. 150 22

Staircase. 150 22

Corridors. 100 22

Outdoor Entrances. 30 22

Casual Assembly Work. 200 25

Rough / Heavy Work. 300 28

Medium Assembly Work.

500 25

Fine Assembly Work. 1,000 22

Precision Work. 1,500 16

General Office Work. 500 19

Computer Room. 750 16

Drawing Office. 750 16

Filing Room. 300 22

Shop Counter. 500 22

Super Market. 500 22

ILLUMINATION LEVELS AND LIMITING GLARE:

Location. Illuminance. (lx) Limiting Glare Index.

Class Room. 300 16

Laboratory. 500 16

Public House Bar. 150 22

Restaurant. 100 22

Kitchen. 500 22

Dwellings:

Living Room. 50 NA.

Reading Room. 150 NA.

Study Room. 300 NA.

Kitchen. 300 NA.

Bed Room. 50 NA.

Hall. 150 NA.

Library – Reading Area. 200 19

Library – Tables. 600 16

Library – Counter. 600 16

LIGHTING LEVELS:(lx)

Activity. Area.

100

Casual seeingCorridors, changing rooms, stores

150

Some perception of detailLoading bays, switch rooms, plant rooms

200

Continuously occupiedFoyers, entrance halls, dining rooms

300

Visual tasks moderately easyLibraries, sports halls, lecture theatres.

500

Visual tasks moderately difficult

General offices, kitchens, laboratories, retail shops.

750

Visual tasks difficultDrawing offices, meat inspection, chain stores.

1000

Visual tasks very difficultGeneral inspection, electronic assembly, paint work, super markets.

1500

Visual tasks extremely difficult

Fine work and inspection, precision assembly.

2000

Visual tasks exceptionally difficult

Assembly of minute items, finished fabric inspection.

ELECTRICAL FORMULAS:Demand for Power (kW) = System Input Wattage (W) ÷ 1,000

Energy Consumption (kWh) = System Input Wattage (kW) x Hours of Operation/Year

Hours of Operation / Year = Operating Hours / Day x Operating Days / Week x Operating Weeks / Year

Lighting System Efficacy (Lumens per Watt or LPW) = System Lumen Output ÷ Input Wattage

Unit Power Density (W/ Sq.M.) = Total System Input

ELECTRICAL FORMULAS:Wattage (W) ÷ Total Area (Sq. m.)

Watts (W) = Volts (V) x Current in Amperes (A) x Power Factor (PF)

Voltage (V) = Current in Amperes (A) x Impedance (Ohms) [Ohm's Law]

ECONOMIC FORMULAS:Simple Payback on an Investment (Years) = Net Installation Cost ÷ Annual Energy Savings.

5-Year Cash Flow = 5 Years - Payback (Years) x Annual Energy Savings.

Simple Return on Investment (%) = [Annual Energy Savings ÷ Net Installation Cost ] x 100

DESIGN FORMULAS:Footcandles & Lumens

Footcandles (fc) = Total Lumens (lm) ÷ Area in Square Feet

1 Lux (lx) = 1 Footcandle (fc) x 10.76

Lux = Total Lumens ÷ Area in Square Meters

SUNLIGHT:400 lux: Sunrise or sunset on a clear day.

1,000 lux: Overcast day.

10,000–25,000 lux: Full daylight (not direct sun)

32,000–130,000 lux: Direct sunlight.