No of bulb used in a room

Are you trying to find how many bulbs are needed for your room? Then this article is best for you. For different type of room in different type of places, we need a suitable size and number of bulbs. 

How to find total number of bulbs for room?

Here we are going to answer "How to find total no of bulbs in a room?" The total no of bulbs in a room depends on its size. For a house/room electrical design, it is very important to find the no of bulbs required so that we can install required switches, bulb holders also estimates the cost of bulbs, installation etc. As an electrical engineer, we have to design and estimate all parameters like bulbs, switches, holder, cost etc. Here we are ready to go to find the total required numbers of bulbs for a room.

Calculation of No of bulb used in a room

For finding total no of bulbs required, we have to use a formula. That is

total no of bulb required (N) = (E x A) / (∅ x η_u x η_m )

where,

E = Illumination required for room

A = Area of room

∅ =  Lumen output of each lamp = Wattage of each lamp x efficiency of each lamp

η_u = Utilization factor

η_m = Maintenance factor

It will be easy to understand this from a example:-

For a hall of size 20m x 30m x 10 m is given for design which is need to be illuminated by 2 x 200 watts lamp. The room needs illumination level of 250 lumen per meter square (Lumen/meter² ). Calculate the number of lamps required for that room where utilization factor is 0.9, maintenance factor is 0.85 and efficiency of lamp is 50 lumen/watt.

Solution:- 

Given,

total lumen output from each lamp , ∅  = 2 x 200 x 50 = 20000

Area = 20 x 30 = 600 meter² 

illumination level, E = 250 Lumen/meter² 

utilization factor = 0.9

maintenance factor = 0.85

Now, total no of bulb required (N) = (E x A) / (∅ x η_u x η_m )

                                                        = (250 x 600) / (20000 x 0.9 x 0.85)

                                                        = 9.80 ≈ 10 

Hence, total no of bulb required is 10.

You have got the total number of bulbs/fixtures but how many bulbs in row and column i.e. length and breadth.

Now, the no of bulb on length side and breadth (row and column) side can be found by using,

Approximate spacing, S = √(A / N)

 no of bulbs/fixtures in each row,

Nrow = length of room / S

no of bulbs in each column,

Ncolumn = breadth of room / S

For above question, we need to calculate the number of bulbs in row and column,

Approximating spacing,

S = √(A / N)

  =  √(20 x 30 / 10)

  = 7.74

total no of bulbs in row is, 

Nrow = length / S

            = 20 / 7.74

            = 2.58 ≈ 3

total no of bulbs in column is,

Ncolumn = breadth / S

                = 30 / 7.74

                = 3.87 ≈ 4

Here we get total no of bulb in row is 3 and in column is 4 so the total no of bulb is (3 x 4 = 12) which is actual no of bulb for that room.

But in actual practice as a designer/engineer, no one will give you the value of utilization factor and maintenance factor. And the illumination level required is also not given by owner but you can get it from table or can google search.

Generally some important illumination level required values are as follows:- 

House :- living room, kitchen, bathroom requires 150 lux

               Reading room requires 250 -500 lux

Sports ground :- Stadium requires 200 - 400 lux

                            Football field requires 100 - 200 lux

                            Tennis court requires 250 - 500 lux

Office :- Reception requires 150 lux

                conference room, general office, computer office requires 300 - 500

School :- common room, stairs requires 150 lux

            :- class room, library, hall, workshop requires 150 - 300 lux

Hotel :- Reception, bed room, stairs requires 150 lux

                Account, writing desk requires 200 - 500 lux

Hospital :- Waiting room, wards, casualty requires 150 lux

                    Lab, operation theater, dispenser requires 300 - 500 lux

Here lux = Lumen/meter² 

From these values, we can calculates total no of bulbs/fixture required.