## Input information

**These are the input data for the following calculation:**

- An office area has length: 20 meter; width: 10 meter; height: 3 meter.
- The ceiling to desk height is 2 meters.
- The area is to be illuminated to a general level of
**250 lux**using twin lamp 32 watt CFL luminaires with a SHR of 1.25. - Each lamp has an
**initial output**(Efficiency) of 85 lumen per watt. - The lamps
**Maintenance factor (MF)**is 0.63 ,Utilization Factor is 0.69 and space height ratio (SHR) is 1.25.

### Calculation in 8 steps

#### 1. Total wattage of fixtures:

Total wattage of fixtures = Number of lamps x each lamp’s watt. |

Total wattage of fixtures = 2 × 32 = 64 Watt. |

#### 2. Lumen per fixtures

Lumen per fixtures = Lumen efficiency (Lumen per Watt) x each fixture’s watt |

Lumen per fixtures = 85 x 64 = 5440 Lumen |

#### 3. Number of fixtures

Required number of fixtures = Required Lux x Room area / MF x UF x Lumen per fixture |

Required number of fixtures = (250 x 20 x 10) / (0.63 × 0.69 × 5440) |

We will need 21 fixtures |

#### 4. Minimum spacing between each fixture

The ceiling to desk height is 2 meters and space height ratio is 1.25, so: |

Maximum spacing between fixtures = 2 × 1.25 = 2.25 meter. |

#### 5. Number of required rows of fixtures along with width of room

Number of rows required = Width of room / Max. spacing = 10 / 2.25 |

Number of rows required is therefore = 4. |

#### 6. Number of fixtures required in each row

Number of fixtures required in each row = Total Fixtures / Number of rows = 21 / 4 |

Therefore, we have 5 fixtures in each row. |

#### 7. Axial spacing between each fixture:

Axial spacing between fixtures = Length of room / Number of fixtures in each row |

… and that would be: 20 / 5 = 4 Meter |

#### 8. Transverse spacing between each fixture:

Transverse spacing between fixtures = Width of room / Number of fixtures in row |

… and that would be: 10 / 4 = 2.5 Meter. |

## 5 things to conclude

**So far, we have been calculated the following:**- Number of rows with lighting fixtures =
**4** - Number of lighting fixtures in each row =
**5** - Axial spacing between fixtures =
**4.0 meter** - Transverse spacing between fixtures =
**2.5 meter** - Required total number of fixtures =
**21**

Majd

Hey, i was wondering how to find the Utilization Factor for a light?

rajeev

dear sir

i need to know the no of lights ( high bay required) for a shed having lenght,breadth and height of 73 mts 33 mtrs and 9 mtrs respectively. the highbay have 130 lumens per watt at source 120 beam angle and are of 100 watts . the lux level is of 250 . can you please let me know the no of fixtures requird

thanks

divya

can u help how to calculate illumination factor for 4 tube lights of 40 watts inside and outside led bulbs are putting on a hub how to calculate the spacing

jamshid

How i can calculate SHR in lighting calculation

SUBRAMANI

i need to know what is the relation between No. of Light and lumens while increasing mounting height of the light.

also what is the recommendation for industries. how can i able to find Spacing Height Ratio? Where to i got this?

moubani banerjee

20x 400w son floodlights are mounted on a 12pole at the middle of each of the side of a square area of 40m side. calculate utilization factor ,the average illumianace on the area, the illuminance at any corner point. GIVEN : the total initial lamp lumen is 50 klm, D.F=0.8, MF=0.75, loss factor=0.9

koua

It’s verry interesting!

Emmanuel

Your work is very good . I appreciate it so much . My question is , if u are really keen to share your knowledge in the field of electrical Engineering , how would one communicate to you ?

Said

Thank you very much.

Mostafa Elsayeed

Your clarification and description is very interesting and simple, thanks too much, in this regard I want to ask some questions:

1. should i take into consideration the clean factor (1.27-1.33), ie the values of numbers will be multiplied with this factor and therefore no of luminaries will increase.

2. for a certain space, it should be identified the color of ceiling, wall& floor and material type to get the reflecting factors and g with room index through the data table of the chosen lamp to get UF and this data no longer be available for the new models of lamps! how can we deal with this issue? appreciate your reply.

dawsam abdallah

how can i download this in pdf form

awny

How can I download this article format PDF

Thank you very much

mohammed nizamuddin

Number of rows with lighting fixtures = 4

Number of lighting fixtures in each row = 5

Required total number of fixtures = 21

TOTAL NUMBER OF FIXTURES SHOULD BE 20 OR 21?? IF 21 PLEASE EXPLAIN ? ACCORDING TO DATA AT THE BOTTOM SIDE (ALSO MENTIONED IN 1ST 2 LINES OF COMMENT) I THINK SO TOTAL NUMBER OF FIXTURES SHOULD BE 20.

REGARDS

mohammed nizamuddin

how to download this one?

kavi

tiny mistake in figures..

step 4: spacing should be 2.5 instead of 2.25…1.25×2=2.5..

step 5: the calculation sticks to 10/2.5=4

Alexander Nowak

Nice demonstation of a classical calculation without the help of a fat light planning software.

But let me please make some comments: A lighting level of 250 Lux for an office area is not compliant to standards. For offices you should plan with 500 Lux instead.

Also I would consider to use not CFL but linear fluorescent lamps (T5), which have much higher efficiency of approx. 100 Lumen per Watt. Than you get also a better MF of 0,8 and this together reduces the number of fixtures.

ugbana joseph

Thanks a lot its useful mostly to me because am still a fresher in the field of engineering.