How to calculate the number of lamps or lighting power for different types of rooms

10 June 2025

Why calculate lighting

Indoor lighting is calculated to determine how many lamps and bulbs need to be installed, as well as how brightly the working or living environment should be illuminated. This is important not only for comfort, but also for compliance with government regulations. If these requirements are violated, the company faces fines. To avoid problems and create favorable conditions for work, you need to know how to correctly determine the level of lighting. Next – all about calculation methods.

lighting calculation

State standards

Lighting standards depend on depending on the type of room and the tasks performed in it. For example:

Living room, kitchen – 150 lux
Children's room – 200 lux
Office, study – 300 lux
Classroom – 500 lux

These values take into account the peculiarities of vision, visual load, color of surfaces, etc. In Ukraine, the norms of GSN V.2.5-28:2018 are in force (since 2019), which regulate both natural and artificial lighting.

How to calculate the illumination of a room

Previously, the level of illumination was determined by the power of lamps, but with the advent of LEDs this became irrelevant. The modern method is based on the luminous flux (measured in lumens).

Formula for calculating the luminous flux:

Norm (lux) × Area (m²) × Ceiling height coefficient = Total need in Lm

The coefficient depends on the ceiling height:

2.5–2.7 m → 1
2.7–3 m → 1.2
3–3.5 m → 1.5
3.5–4.5 m → 2

Example: For a living room of 30 m² with a height of 2.5 m:

150 × 30 × 1 = 4500 Lm

The number of lamps depends on the type:

Lamp type	Power	Luminous flux	Number of pieces required
Incandescent lamp.	40 W	470 Lm	10
LED	10 W	750 Lm	6

Calculation of the illumination of the working surface

For working areas, a more accurate formula is needed:

N = (E × S × Kz × z) / (Ф × η)

N — number of light sources
E — illumination standard (lux)
S — surface area
Kz — safety factor (1.5 for offices)
z — unevenness of lighting (1.1)
Ф — luminous flux of one lamp (Lm)
η — luminous flux utilization factor (depends on color and type of room)

Example: A table with an area of 4.5 m² in the office (ceiling 3 m, light walls):N = 300 × 4.5 × 1.5 × 1.1 / (850 × 0.51) ≈ 6 lamps

The results obtained by the formula are approximate. If you need an exact value for a specific object, technical advice or information on the availability of LED products, contact Artled

What else is important to consider

The color of the walls, ceiling, floor: dark colors «absorb» light, so more lamps are needed.
Type of luminaires: the power of the lamps should not exceed the permissible for the luminaire.
Ceiling lights: open or closed, color, material - all this affects the lighting.
Energy efficiency: light-emitting diodes (LEDs) consume less electricity, are more durable and more efficient than fluorescent or incandescent lamps.