Lighting Calculations-Indoor.doc

LIGHTING CALCULATIONS INDOOR

LIGHTING CALCULAIONS - INDOOR

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LIGHTING CALCULATIONS INDOOR

INDEX

INTRODUCTION...........................................................................................................................2 CODES & STANDARDS...............................................................................................................2 PROCEDURE..................................................................................................................................2 CALCULATIONS:..........................................................................................................................3 SAMPLE CALCULATION:...........................................................................................................8 INTRODUCTIONThis Document covers procedure to calculate the illumination level & number fixtures required for indoor by lumen or total flux method.

CODES & STANDARDSUnless otherwise specified in this document, all components and equipment shall be based on the following standard: IEC IS 3646-1 IES PTS 33.34.10.10 International Electro technical Commission Standards Code of practice for Interior illumination Illumination Engineering Society Electrical Engineering Guidelines

2) In case of different standards regarding lux levels, the client specification shall apply.

PROCEDURETo select the right lighting fixture for a specific job there is a simple Four-step procedure.

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The four-step are: 1. 2. 3. 4. Determine Area Lighting needs Select type of Lamp Select type of lighting fixture

Calculate number of lighting fixtures required

To select the proper lighting fixture and determine number of lighting fixture required, the following aspects need to be addressed.

Determine Illumination (Lux) Required: Illumination required for the specific area is given in PTS 33.64.10.10. & IS 3646. In case of different standards regarding lux levels, the client specification shall apply.

Area Code Depending on materials or atmosphere within an area, the choice of lighting fixture and lamp is therefore somewhat restricted if the area is classified as hazardous.

Type of Lamp & Lighting Fixture: Check design basis or Lighting fixture specification for type of lamp & Lighting fixture.

CALCULATIONS:For uniform lighting of a specific area, the Lumen method is used to calculate the number of lighting fixtures required. This method takes into account not only the direct light from the lighting fixture, but also that which is reflected from the ceiling, walls and floor. The higher the reflectivity of the surfaces, the fewer number of lighting fixtures required.

Step 1:Calculate Room Index:

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The room index is a number that describes the ratios of the room length, width and height. K Where: L W Hm = = = Room Length Room Width Mounting Height of Fitting (from working plane) = LxW Hm (L+W)

Work Plane = Desk or Bench Height (Note: In office rooms the required no. of lighting fixtures are calculated by considering the working plane height. The working plane height ranges from 0.5 to 1m.) The result of this calculation will be a number usually between 0.75 and 5.

Step 2:Determine Reflectances: Typical Reflectance values are Air Conditioned Ceiling 0.7 0.5 Walls 0.5 0.3 Floor 0.2 0.2

Office Industrial

Step 3: Determine Coefficient of Utilization: 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 reflectances, room shape, polar distribution and light output ratio of the fitting. Coefficient of Utilization Table:

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For the horizontal row select the reflectance that best describes the room. For the vertical column select the room index value K as calculated above. The utilization factor for this fitting in this room is where the row and column intersect. For LOR (Light output ratio) value refer respective vendor catalogue. (Note: Coefficient of Utilization table for some fixtures refer last page of this document) Step 4 Maintenance Factor: This takes account of the depreciation over time of lamp output and dirt accumulation on the fitting and walls of the building. Page 5 of 15

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Air

Conditioned

M.F 0.8 0.7 0.6

Office Clean Industrial Dirty Industrial

Step 5 Calculate no. of Lighting Fixtures required No. of FittingsWhere: L W = = Room Length Room Width

=

L X B X Lux Level required

Lumen output of the lamp X MF X COU

MF COU

= =

Maintenance Factor Coefficient of Utilization

For Lumen output of the lamp refer respective vendor catalogue. SPACING CRITERIA: Spacing criteria is the maximum ratio of spacing to mounting height of the luminaire above the working plane that provides reasonable uniformity of illumination within the space 1. For luminaires using essentially point sources of light, such as incandescent or HID lamps, the number of luminaires per row should be in proportion to the width-to-length ratio of the room.

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2.

For fluorescent luminaires, it is necessary to first establish the

maximum number that can be installed in one row. The maximum number is calculated by subtracting at least 0.3 meter from the room

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length

and

then

dividing

by

the

length

of

the

luminaire.

3. The exact spacing between rows is calculated by dividing the room width by the number of rows. 4. Spacing between luminaires in each row is calculated by dividing the room length by the number of luminaires per row. 5. Spacing between the outer luminaires and the adjacent wall is onehalf of the luminaire spacing 6. If desks or other work areas are to be located alongside the walls, then the wall-to-luminaires spacing should be reduced to one-third of the luminaire spacing 7. No. of fittings in a row =

Total x L/W Total x W/L

No. of fittings in a Column = SAMPLE CALCULATION:

A general open plan office has dimensions 12 (L) X 8.5 (W) X2.8 (H) Page 8 of 15

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Lux level required Lamp Used

= =

400 40W fluorescent = 1800W

Lumen output of the lamp

Working area is at a height of 0.8m Mounting height = = Step 1: Room Index = 12 x 8.5 2 x (12+8.5) = Step 2: Reflectance values considered as below Ceiling reflectance Wall reflectance = Floor reflectance a Step 3: Coefficient of Utilization: By considering Ceiling reflectance as 0.7 Wall reflectance as 0.5 Room Index = 2.5 (Calculated above) The Coefficient of Utilization Shall be 0.55 Step 4: Maintenance Factor shall be 0.8 for Air conditioned office Step 5: Calculate no. of Lighting Fixtures required Page 9 of 15 = 0.5 = 0.2 0.7 2.48 ~ 2.5 2.8-0.8 2m

LIGHTING CALCULATIONS INDOOR

No. of Fittings No. of Fittings = Spacing Criteria:

= =

L X B X Lux Level required

Lumen output of the lamp X MF X COU

12x8.5x400

1800x0.8x0.55 52 nos.

No. of fittings in a row = 8.5

=

52 x 12/8.5

No. of fittings in a Column = =6

Total x W/L

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Distance between the Fixtures along length = Space at end of Row = = Space at end of Row = =

=

12/9

1.33 Meters 1.33/2 = 8.5/6 0.66 Meters 1.41 Meters = 1.33/2 0.708 Meters

Distance between the Fixtures along width

SAMPLE

COEFFICIENT

UTILIZATION

TABLE

FOR

DIFFERENT

FIXTURES:

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