Updated 30-X-2011
Lamp Nomenclature
Fluorescent Colours
Early History
Operating Principle
Phosphor Types
Gas Fillings
Lamp Lifetime
Switching Frequency
Ambient Temperature
Operating Frequency
Dimming Operation
Lamp Designs
T12 Argon
T8 Krypton
T5 Krypton
T5 Miniature
(Very) High Output
Rapid Start
Instant Start
Non-Linear Tubes
Compact Fluorescent
Lamp Designs
Switch Start
Tandem Switch-Start
Semi-Resonant Start
Rapid Start
Instant Start
Resistor Ballast
High Frequency
DC Operation

Dimming Operation

Dimming of fluorescent lighting offers significant benefits - giving users control of their own lighting, and realising energy savings. In certain environments it is a must, for instance in a lecture theatre to modify the lighting level when beaming a presentation. In other applications the flexibility it gives to people has significant value, allowing them to match the illuminance on the working plane to their personal needs.

The control systems surrounding dimming of fluorescent lamps are becoming increasingly complex, for instance when linked to a daylight harvesting system to provide artificial lighting only at times of reduced natural illumination. Dimming creates a rich visual experience and adds flexibility to any room, providing the right lighting environment for a variety of activities.

An added bonus is the fact that modern electronic ballasts permit a reduction in power consumption in parallel with the reduced light level, and this presents a valuable energy saving opportunity. A further advantage is the use of dimming as an alternative to repeated on/off switching. In this fashion substantial energy savings can be realised but without negatively impacting lamp life.

Traditionally, dimming of fluorescent lamps has presented significant challenges. If the power dissipation in the lamp is reduced too far, the electrode temperatures will fall such that their emission decreases and that leads to excessive wear and short life due to sputtering of the emissive material. Cathode preheating needs to be maintained during dimming to the lower levels to avoid this problem. Reignition of the discharge also becomes troublesome at very low currents, and in the past special tubes employing metal stripe ignition aids internally connected to one of the main electrodes were necessary.

The advent of the modern electronic ballast has greatly simplified matters. By providing a variable signal voltage to the ballast, generally over the range 1 to 10 Volts, it can be triggered to regulate lamp power and automatically takes care of providing the necessary cathode heating and reignition voltage. Standard lamp types can be used in all cases, and there is no further need to specify the former metal striped tubes.