About Lighting

Consideration about Illumination of Buildings 1. General a. Definition: A measure of the amount of light falling on a surface. It is defined as: 'the density of the luminous flux incident on a surface'. It is the quotient of the luminous flux by the area of the surface when the latter is uniformly illuminated.

b. Unit: One foot candle is the illuminance at a point on a surface which is one foot from, and perpendicular to, a uniform point source of one candela. One lumen uniformly distributed over one square foot of surface provides an illumination of 1 foot candle. One lux is the illuminance at the same point at a distance of 1 meter from the source.

c. If you work in a feet, your results will be in foot candles  1 foot candle = 1 lumen/square ft. If you work in meters, your results will be in lux –  1 lux = 1 lumen/square meter 1 foot-candle ≈ 10.764 lux.

2. How many lighting fixtures are required for a Room 2-1. The items to be considered

a. The Purpose of this step to calculate “Numbers of Lighting Fixture” - The final goal of these steps is “To calculate power consumption of Lighting which will be consuming in total electric power for room”.

Because we can know required numbers of lighting fixture from these calculations under proper intensity of illumination that is defined by standards

b. To determine the type and bulb shape of Lamp - This is basic step to proceed for calculation. As per lamp model of manufacturer, there are many type, bulb shape, consuming power and initial brightness (“Flux”) in catalogue we can read. So Determining type, shape, watt and many detail specifications should be required and fixed before calculations - Summary of Lamp type used for this calculation

Installed place

Item used

Double / Single

Power(watt)

Camp room(except S2, S6)

Fluorescent

Double

20

Room of S2 and S6

Fluorescent

Double

40

Incandescent

Single

40

Ablution for S6

Fluorescent

Double

20

Water-proof

Food Storage

Incandescent

Single

20

Weather-proof

Fluorescent

Double

40

Sodium Vapor Flood Light

Case by Case

700 / 1000

Toilet for camp and office

Office Outside Sports Court

Remarks

50 lm/watt

c. The Meanings of factor – First we need to know several technical words in order to understand for these.

(1) Utilization factor- This is a value between 0 and 1 that represents the percentage of total lamp lumens in the room that fall on the work plane. It takes into account the room reflectance (especially surface of stuff in room), room shape, polar distribution and light output ratio of the fitting. Some typical reflectance of wall and ceiling are shown by below illustration.

(2) Maintenance factor - also called Light Loss Factor the proportion of the illuminance provided by a lighting installation in a room after a set time compared with that occurred when the room was clean. It takes into account that dirt accumulates on room surfaces and reduces surface reflectance. Without detailed knowledge of a maintenance plan one sets MF = 0.8

(3) Room Index - The room index is a number that describes the ratios of the room’s length, width and height. If room index is getting higher and higher, means brighter than lower index (Good reflectance) Actually This Room index is not affected to calculate the numbers Lamp to be installed, however this only is used for just reference data that shows the relations between Room index and Utilization Factor as followed illustrations.

Formula:

Where: RI = Room Index L = Room Length W = Room Width Hm = Mounting Height of Fitting from working plane(Not Room Height)

2.2. Calculation method a. In rooms lit with a uniform array of luminaries and where the minimum lighting level in the room is not to be less that 70% of the maximum level, the lumen method of lighting design can be used. This is the simplest method of calculating the overall illumination level for such areas. It is accurate enough for the majority of purposes, and is the calculation most used by lighting engineers when determining the number of luminaries for a given lighting level.

The simple formula is as follows: E=F/A Where: E = average (or minimum) illumination level at the work plane (lux), F = useful lumen output of all sources (lumens) and A is the total surface area of the working plane (m²).

This is given by rearranging the formula as follows: F=AxE It must be realized that the resultant value is not the total lamp lumens as not all of the light produced by each lamp actually reaches the work plane. Many factors affect the amount of light reaching the work plane: •

The size and proportion of the room.

•

The height of the light fixtures above the work plane.

•

The reflectance of wall and ceiling surfaces.

•

The nature of the light fixture and its distribution of light.

•

Light loss due to ageing, dust collection and yellowing.

•

Atmospheric particles such as smoke or dust.

a. As a result, the steps required in using the Lumen Method of lighting design are as follows:

(1) Select Required Illumination – 100 Lux? 200 Lux? 300 Lux? And Brighter? Most countries have a set of minimum lighting levels for various tasks as per each national standard. The designer must determine what the minimum required illumination level is for their particular application on proper criteria. Please refer to following table (Required Illumination Table of JGC and JAPAN INDUSTRIAL STANDARDS)

Required illumination level for ea Temporary Building

Room / C

Client Pioneer Office

Pione

JGC Pioneer Office

Pione

Conference Room

Pione

W aiting Room

Pione

Fence / Street

All

Guard House

All

All Shed / Generator shed

All

External Light

All

Living Room for S1, S2

Cam

Bed Room for S1 ~ S6

Cam

(2) Determine Received Flux – Check the manufacturer’s data sheet This is simply a matter of calculating the total surface area over which the required illuminance is to be distributed and multiplying this by the required illumination level using the formula F = AE. From this, the total installed flux can be determined. Following Table is summarized value from G.E Lighting Fixture

(3) Select a Light Fitting/Type –Fluorescent? Or Incandescent? Double or single? A preliminary assessment must be made of the type of lighting required, a decision most often made as a function of both aesthetics and economics. This fitting may prove unsuitable for the lighting task; however, the next few steps are used to determine this.

(4) Determine Mounting Height – Mounting on ceiling? Or Hanging type? The distance from the source to the working plane is very important as it is a major determinant of the final illumination level. This is simply a function of the inverse square law.

(5) Determine Coefficient of Utilization (U) Using tables available from manufacturers, all architects offices will have several; it is possible to determine the coefficient of utilization for different light fittings if the reflectance of both the walls and ceiling is known, the room index has been determined and the type of luminaries are known. Usually this Utilization factor is unable to specify so that we must have manufacturer's photometric data sheet for executing exact design for lighting installation. But we can assume and set that value as rough range; 0.8(good reflectance) ~ 0.6(not so good)

(6) Determine Maintenance Factor (M) The maintenance factor is based on how often the lights are cleaned and replaced. It takes into account such factors as decreased efficiency with age, accumulation of dust within the fitting itself and the depreciation of reflectance as walls and ceiling age. Usually we will use 0.8 for Clean room/Office or 0.6 / 0.7 for other space with dirt.

(7) Determine Number of Fixtures This is done by first applying the above factors to the received flux in order to determine the installed flux. This if achieved using the following formula; E (required F (total fluxillumination of lamp) at work plane) x A xU xM (area of work plane)

N (no’s of Fixtures to be installed) =

From the installed flux, the number of fixtures required can be determined by simply dividing by the total output of each selected light source.

Example) Design a lighting installation for office conference room so that the average illuminance is 300 lux on the horizontal working plane, using the data which are Room dimensions: 5 m long x 4 m wide x 2.5 m high, 0.8 of Maintenance factor, Total flux of 40W Single Fluorescent = 3000 Lx)

Solution)

a. We can use below formula to obtain Numbers of lighting fixture

E (required F (total fluxillumination of lamp) at work plane) x A xU xM (area of work plane)

So this formula will be 300Lx * 20 m2 / 3000 Lx * 0.7 * 0.8 = about 3.6

b. Finally we need to install 4 single fluorescent lamps of 40W (or 4 Double fluorescent lamps of 20W) for bright conference room.

c. So Total power consumption is 40W x 4 Ea of lamp, 200 Watt.

Reference - 1) Table for illumination of Temporary facility building (Click to open with Ctrl Key) Reference - 2) Calculation sheet (Click to open with Ctrl Key)