Fluorescent lamps

From Electrical Installation Guide

See also "Lighting circuits" for more details

Fluorescent lamps and related equipment

The power Pn (watts) indicated on the tube of a fluorescent lamp does not include the power dissipated in the ballast.

The current is given by:

Where U = the voltage applied to the lamp, complete with its related equipment.

If no power-loss value is indicated for the ballast, a figure of 25% of Pn may be used.

Standard tubular fluorescent lamps

With (unless otherwise indicated):

  • cos φ = 0.6 with no power factor (PF) correction[1] capacitor
  • cos φ = 0.86 with PF correction[1] (single or twin tubes)
  • cos φ = 0.96 for electronic ballast.

If no power-loss value is indicated for the ballast, a figure of 25% of Pn may be used.

Figure A6 gives these values for different arrangements of ballast.

Fig. A6 – Current demands and power consumption of commonly-dimensioned fluorescent lighting tubes (at 230 V-50 Hz)
Arrangement of lamps, starters and ballasts Tube Power (W)[a] Current (A) at 230 V Tube Length (cm)
Magnetic Ballast Electronic Ballast
Without PF correction capacitor With PF correction capacitor
Single tube 18 0.20 0.14 0.10 60
36 0.33 0.23 0.18 120
58 0.50 0.36 0.28 150
Twin tubes 2 x 18 0.28 0.18 60
2 x 36 0.46 0.35 120
2 x 58 0.72 0.52 150
  1. ^ Power in watts marked on tube

Compact fluorescent lamps

Compact fluorescent lamps have the same characteristics of economy and long life as classical tubes. They are commonly used in public places which are permanently illuminated (for example: corridors, hallways, bars, etc.) and can be mounted in situations otherwise illuminated by incandescent lamps (see Fig. A7).

Fig. A7 – Current demands and power consumption of compact fluorescent lamps (at 230 V - 50 Hz)
Type of lamp Lamp power (W) Current at 230 V (A)
Separated ballast lamp 10 0.080
18 0.110
26 0.150
Integrated ballast lamp 8 0.075
11 0.095
16 0.125
21 0.170


  1. ^ 1 2 “Power-factor correction” is often referred to as “compensation” in discharge-lighting-tube terminology.
    Cos φ is approximately 0.95 (the zero values of V and I are almost in phase) but the power factor is 0.5 due to the impulsive form of the current, the peak of which occurs “late” in each half cycle