How to calculate the needs of Lamps in a room

Lighting needs in a room

How many lights are needed to light a room?

How many watt lamps are needed in order to provide optimal lighting in a room?

1 Watt Lamp can provide illumination of 75 Lumen.

For those of you who are currently planning to install lighting installation in a room that may be new you wake up. Maybe this time you just finished building a house, but still confused how to determine how many lights you will put in the room in your house. Or you have installed some lights in the room, but have not been able to provide the desired lighting results. On the one hand, we certainly want enough lighting for a room, so that the room we can use for various activities. But on the other hand you also must have a calculation of how to lamp lighting that you will install is not too excessive, but with optimal lighting results, so it will not cause waste of electrical power. Therefore, to get how many watts of light or how many number of lamps you will put in a room for optimal indoor lighting, it is necessary to do a good calculation to get the number of lights or how many watt lamps needed a room. Actually, the right question to represent the above questions is how much lighting is needed to illuminate a room.

How much Lighting does a room need?

So, if we talk about the lighting or light, then we will need to know some of the commonly used light units, namely:


Candela is one of the lighting units. From her language Candela can be interpreted as big as candle lighting.


Lumen is one of the units of Lighting. In LUMEN lighting units, state how much lighting is generated from a single light source.


Lux is one of the lighting units. Lux expresses the amount of Light that is present in a room that receives Lighting from a light source. Once we know some lighting units, then how to determine the number of lights to illuminate a room.

Also read: how to choose the lights

To determine the amount of lighting a room, there are some things we should know, among others:

  1. The type of room to be fitted with lighting

The room to which the lighting lamps will be installed. The level of lighting has different values ​​according to the type and function of the room. Below you can see some of the standard lighting values ​​in a particular room.

The room is in the House of Residence

  • TERRACE The standard lighting is 60 LUX
  • GUEST ROOM Standard lighting is 120 – 150 LUX
  • EATING ROOM Standard lighting is 120 – 250 LUX
  • WORKING ROOM Standard luminaries are 120 – 250 LUX
  • BEDROOM The standard lighting is 120 – 250 LUX
  • BATHROOM Standard lighting standard is 250 LUX
  • KITCHEN Standard lighting is 250 LUX
  • GARAGE Standard lighting is 60 LUX

The room is in the office

  • THE DIRECTOR ROOM The standard lighting is 350 LUX
  • WORKING ROOM Standard lighting is 350 LUX
  • COMPUTER ROOM Standard lighting is 350 LUX
  • MEETING ROOM Standard luminaries are 300 LUX
  • THE IMAGE ROOM The lighting standard is 750 LUX
  • WAREHOUSE ARCHIVES The standard lighting is 150 LUX
  • ROOMS OF ACTIVE ARCHIVES The default luminaries are 300 LUX

The room is inside the School

  • CLASS ROOM The standard lighting is 250 LUX
  • LIBRARY The standard lighting is 300 LUX
  • LABORATORY The luminance standard is 500 LUX
  • THE IMAGE ROOM The lighting standard is 750 LUX
  • KANTIN Standard lighting is 200 LUX

The rooms are inside Hotel and Restaurant

  • LOBBY & CORRIDOR The luminance standard is 100 LUX
  • SERIOUS ROOM Standard luminaries are 200 LUX
  • EATING ROOM Standard luminaries are 250 LUX
  • KAFETARIA Standard luminaries are 250 LUX
  • BEDROOM The standard lighting is 150 LUX
  • KITCHEN Standard lighting is 300 LUX
  1. The size of the room, such as the size of the length and width of the room.
  2. How much power or Watt for one lamp to use.
  3. 1 Watt lamp = 75 Lumen lighting

After some of the things we know, we can then calculate how many lights we need to give the desired lighting in the room.

Using Formulas to determine the number of lighting lamps in a room.


Explanation the above formula, is:

N = Number of light points

E = Powerful lighting (Lux), house or apartment standard 100lux – 250lux

L = Length of room in Meter unit

W = Width of room in Meter unit.

Ø = Total value of lighting in LUMEN unit

LLF = (Light Loss Factor) or Factor of loss or loss of light, the usual value is between 0.7-0.8

Cu = (Coeffesien of Utillization)

N = Number of Lights in 1 point

As an example calculation to find out how many lamps need in a room, we can take the following data:


A room with a bedroom size of 5 meters in length and 4 meters width in the house, to be installed 40 Watt TL lamp, How many TL 40 Watt lamps are needed to provide good lighting in the room?

Is known:

Can we see, from the above strong standard lighting data that for the room The bedroom at the residence is: 120 Lux – 250 Lux.

We take the middle value around 200 Lux

Then it is known, E = 200 Lux.

Length of room or L = 5 meters

Width of room or W = 4 meters

Lumen value of lamp or Ø = 40 Watt x 75 Lumen

Ø = 3000 Lumen.

For direct lighting system with the color of ceilings and bright walls, Coefficient or CU (coefficient of utilization) value is: 50-65%.

For this, we can grab the lowest value of 50% or 0.5

Light loss factor (LLF) = 0.7-0.8. LLF dependent; Cleanliness of light source, lamp shade type, shrinkage of light from lamp surface, and others

LLF value we take the value of = 0.7

The number of lights in a single point (n) is 1


N = 3.8 (rounded to 4 pieces of light)

It is found that the number of lamps needed to provide lighting in the bedroom in the dwelling house is as much as 4 Fruits with lights used is TL 40 Watt.

Or the amount of watts needed is 4 x 40 watts = 160 watts.

That’s how to calculate the amount of Lamp we need to provide good lighting in a room.

Hopefully provide useful information for all of us!