Room Lighting Calculator
About Room Lighting Calculation
This calculator estimates the total luminous flux required for room lighting based on a target illuminance value. Then it either determines the luminous flux per luminaire when the number of luminaires is known, or it calculates the required number of luminaires when the luminous flux of one luminaire is known.
The calculation is intended for a preliminary lighting selection in rooms and for comparing luminaire options by lumens and quantity.
Reference points and recommendations
Target illuminance Em
Illuminance Em is entered in lux (lx) as the target average value on the working plane or on a typical surface in the room. Commonly, users refer to the requirements of EN 12464-1 (indoor workplaces) and EN 12464-2 (outdoor workplaces).
Units are linked as follows: 1 lx = 1 lm/m2. This allows you to convert a lux target to the required luminous flux in lumens through the area.
Room area A
Area A is used in m2. If length and width are known, the area is calculated as the product of the sides. If the area is entered directly, it is used without recalculation.
A = L × W
where L is length (m). W is width (m). A is area (m2).
Maintenance factor k
Maintenance factor k accounts for the reduction of illuminance during use and provides a safety margin for conditions. The calculator offers fixed values k = 1.0, 1.2, 1.5, 2.0.
Practical meaning is as follows. With k = 1.0, no margin is applied. With k = 1.2, moderate losses are often considered. With k = 1.5, more noticeable losses and uncertainties are covered. With k = 2.0, a large margin is used when operating conditions are unfavorable or the lighting level requirements are higher.
Required total luminous flux Φtotal
Total luminous flux Φtotal (lm) is calculated from the target illuminance, the area, and the maintenance factor. The calculation logic is based on the lumens per area relationship and results in the required “lighting capacity” for the room.
Φtotal = Em × A × k
where Em is target illuminance (lx). A is area (m2). k is the maintenance factor. Φtotal is the required total luminous flux (lm).
Selecting the final result by mode
“By number of luminaires” mode uses the entered quantity N (pcs) and determines the luminous flux required per luminaire to achieve the total required flux. The result is rounded up to a whole lumen.
Φ1 = Φtotal / N
“By luminous flux of 1 luminaire” mode uses the entered luminous flux per luminaire Φ1 (lm) and determines the required number of luminaires. The result is rounded up to a whole number.
N = ceil(Φtotal / Φ1)
Calculated illuminance (E × k)
Calculated illuminance in the results shows the target value with the maintenance factor applied. This is a convenient reference to see what target level “with margin” is used in the calculation.
Emcalc = Em × k
FAQs
Why is luminous flux calculated in lumens while the target is set in lux?
Lux is lumens per square meter. Therefore, with a known room area you can convert the required illuminance (lx) into the total luminous flux (lm) using Φtotal = Em × A × k.
What does the maintenance factor k mean and why is it greater than 1?
The maintenance factor k increases the required luminous flux to account for losses and to provide a margin for conditions. For example, with k = 1.2 the calculation allows 20% more luminous flux than “exactly by the target”.
Why is the number of luminaires rounded up?
If the result is, for example, 6.2 luminaires, you actually need 7. Rounding up with ceil() ensures that the total luminous flux is not below the required value.
Can this calculation accurately estimate illuminance at a workstation?
This is an estimate based on area and total luminous flux. Actual illuminance depends on light distribution, mounting height, surface reflectance, and luminaire optics. For a precise design, a lighting calculation using photometric data is typically used.
Which illuminance standards are commonly used in Europe?
For indoor workplaces, users often refer to EN 12464-1, and for outdoor workplaces to EN 12464-2. The calculator uses typical Em values as convenient reference points, and Em can be entered manually if needed.