Fluorescent Lamps

What are they?

Fluorescent lamps (FLs) are commonly used across a range of commercial buildings. The standard T8 (26mm diameter) FLs are commonly found in older buildings but in modern buildings and in retrofits the thinner T5 (16mm diameter) FL is often more energy efficient and is increasingly being fitted as standard.

Advantages / Disadvantages

  • Standard technology with excellent industry support
  • Efficiency of lamp depends somewhat on the control gear used, which is not immediately obvious to the untrained eye.
  • The lifespan of fluorescent lamps is negatively affected by switching, so a minimum switch-on period of 10 minutes should be used.
  • Be wary of retrofits that change the lamp without addressing the overall optics of the light fitting.  Lighting system quality can be badly affected by poorly specified retrofits.

Energy efficiency

FLs are the dominant technology for open area office lighting, and are an efficient solution for this.  LED systems are not quite ready to overtake FLs in this application, although this is only a matter of time given the rate of improvement of LED technology.

Shorter lamps of all diameters are less efficient than their longer counterparts.

T8 lamps with electronic ballast and T5 lamps (which always have electronic ballasts) are of approximately equivalent efficiency.  T8 lamps with magnetic ballasts are less efficient than either.

The final efficiency however must always be judged based on the total installation (lamps + fitting + diffuser + fitting arrangement) rather than the lamps, as a poorly designed T5 installation can have a poorer efficiency than a well designed T8 installation, even if the latter uses magnetic ballasts.

Running costs

Lamps, starters and ballasts require replacement from time to time. Maintenance costs are equivalent for all lamp types.

Retrofit / improvement opportunities

T5 FLs retrofit adapters are available to enable T5 lamps to be directly retrofit into T8 fittings.  However, care is required to ensure that lamp position is not changed in the fitting, as this will affect light distribution in the space and glare.  The adapters also have a relatively short warranty period which can make them a maintenance problem.  T5 lamps also have a lower light output than T8 lamps so care is required to ensure that the final installation maintains adequate light levels.

For older installations, it is preferable to completely redesign the installation either through extensive refurbishment of light fittings or through complete replacement.  This has a longer payback but produces an engineered outcome with a 20 year life.

Lighting refurbishments can be conducted out-of-hours in an occupied office with minimal disruption to tenants.

Applicable buildings

All building types.

Occupant comfort

Badly designed lighting installations can cause significant discomfort due to glare or non-uniformity.  Any refurbishment or new lighting design should be judged on overall lighting quality rather than just illuminance and lighting power density.

Electronic ballasts have a higher lighting quality than magnetic ballasts.

FLs can take a few seconds to ‘warm up’, but this rarely produces problems for occupants.

Maintenance implications

Replacement of FLs on failure leads to a very high maintenance cost on a per lamp basis.  A bulk replacement program at 80% of design life will produce a considerably lower maintenance costs and improved quality of light in the space.


A T5 lamp has a diameter of approximately 16mm compared  to 26mm for a T8 lamp.

A magnetic ballast can often be distinguished from an electronic ballast by the presence of a starter, which is a small cylindrical component.

Questions to ask

  • What lamps are installed – T5 or T8?
  • Have T5 adapters been used?
  • Do the T8 lamps have electronic or magnetic ballasts?
  • What is the Nominal Lighting Power Density as determined via the Buildign Energy Efficiency certificate?

More information

Commercial Building Disclosure program www.cbd.gov.au