How many fluorescent lamp is enough in a room? Steps of simple calculations to determine.

Sometimes your room is too dark? How can we calculate the number of lighting needed in a room? Too little lighting will bring discomfort to our eyes. Therefore, it is important for us to know the minimum lighting required in a room. By seeking a lighting engineer, it is the best way to solve the problem. However, it may be too expensive for many of us.

In fact, for a simple space area, we can calculate the number by ourselves using some basic calculation techniques. Here will show the steps on how to do it with an example:

A lighting design for a small drawing office, 6m², with a 3m ceiling height. Luminaires are to be used whose photometric data are given in Tables. The Luminaires are general diffusing distribution. Triphosphor fluorescent lamps will be used. The lamp will be bulk replaced at 12,000 hours. The office room reflectances are 0.7 ceiling, 0.3wall and 0.2 floor. The lighting is cleaned every year. 

With the information given above,

Step 1: Determine the mounting height

Mounting height(H)= (ceiling height- desk height) 3- 0.8 = 2.2m

Step 2: Determine the room index, K.

K= L x W/ (L+W) x H

K= 6 x 6/ (6+6) x 2.2

K= 1.4

Step 3: Obtain the Utilisation Factor, UF

UF = 0.49

Step 4: Determine Maintenance Factor, MF

MF = LLMF x LSF x LMF x RSMF

MF= 0.84 x 0.75 x 0.88 x 0.9

MF= 0.5

Step 5: Determine the required illumination level

E = 600lux

Step 6: Solve for the total number of luminaires needed

Assume that we use 3 x36W lamp luminaires. Thus, from Table, the initial lumen for a 36W tri-phosphor fluorescent lamp is 3350 Lumen (ø)

N= E x Area/ n x ø x UF x MF

N= 600 x (6x6)/ 3 x 3350 x 0.49 x 0.5

N= 10.2 = 11 luminaires needed

Therefore, a minimum of 11 luminaires is needed for small drawing room, 4 columns and 3 rows will be a good choice (total of 12 luminaires). 

Many of the data can be obtained from the manufacturer. Therefore, the value given in this example might not be accurate. Please use manufacturer's data to ensure the accuracy.

*Tables are obtained from Temasek Polytechnic.

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