Fluorescent Components

The four main elements that govern the energy consumption and/or performance of fluorescent lighting are:

• Ballast
• Lamp
• Starter
• Reflector

Ballast

Ballasts, with the aid of a starter, induce a voltage surge that fires or ignites the lamp. Fluorescent lamps may have an iron core (choke or magnetic) ballast, or a more modern electronic type. These two operate on very different principles. Generally, the characteristics of the ballast and the lamps within a single fixture must be carefully matched to create the correct starting and operating conditions for the lamps to function. As a result, manufacturers often provide a variety of ballasts, allowing for economical and efficient lamp operation. Some fluorescent lamps developed recently are more flexible in this regard.

Iron Core – The iron core type ballast is found in combination with older, energy inefficient tube fixtures. Iron core ballasts are an obsolete technology and should be replaced with electronic ballasts.

Electronic Ballasts – These consist of a filter, a high frequency inverter and a rectifier. They do not require a separate starter as they have an integral ignition device. This igniter provides flicker free starting without the time delay associated with conventional ballasts. Use of electronic ballasts can result in the need for less light fittings in new installations and even some retrofit situations.

Lamp

Tube Size vs. Rating – Commonly used fluorescent lamps are usually tubular in shape with the lamp wattage depending on the linear length of the tube. The most commonly used older style T12 tubes are 1219.2mm (4ft) long with a diameter of 38mm (1.5”) and are rated at 40 watts. The newer lamps are designated as T8 and have a diameter of 26mm (1”) with the most common having a rating of 32 watts on electronic ballasts. The very latest tubes are the slim-line T5 type with a diameter of 16mm (0.63”) and they only operate on electronic ballasts with power ratings from 14 to 80 watts.

Lamp Life – Two lamp life figures are commonly quoted and often confused. One is Rated Life, and the other Economic Life. The Rated Life is the average life of lamps reached when a certain percentage of them fail. To enable benchmark comparisons the international standard IEC60081 is typically used which specifies that this figure be determined under standard operating conditions of 15 minutes OFF after 2 hrs 45 mins ON. The result is typically 20,000 hours for T5s and 18,000 hours for T8s.

Actual operating conditions vary from the IEC standard, so figures of 30,000 can be achieved if lights are left running continuously. On the other hand, a figure of 10,000 might well apply if lights are frequently switched on and off each day. In fact, a faulty starter can cause a lamp to fail in just a few days, versus a potential life of 3-4 years. Each start could reduce lamp life by about 20 minutes, and the high start up current could be equal to that of running the lamp for 20 minutes. The question of whether to turn fluorescent lights off or on relies on competing factors: lamp life reduction and energy conservation.

In practice, it may be more economical to replace lamps before they reach their Rated Life. This point is called the Economic Life and is determined by such factors as the Mortality Curve and the Lumen Maintenance Curves. Other factors involve the specific lighting situation, such as the hours of use and the operating environment, particularly dust and dirt. The Economic Life typically is in the range 60-75% of rated life. 

Starter

Starters are only applicable to old T12 and the later T8 tube. Starters have a major impact on the life of these lamps life, as well as on their performance. If a controlled minimum pre-heating period for the tube’s cathodes does not occur, then the lamp will not ignite correctly. If excessive erosion of the cathode material occurs, starting will be delayed, or, worse still, a constant flickering and possible disruptive noise will occur, which significantly reduces lamp life.

The most common starter used is the cheap, conventional neon glow - bottle or ‘cold start’ type. These starters only last about 3 years, are prone to the above poor starting performance, and give no indication of when a tube is at the end of its life. This means the starter keeps trying to start the lamp, which causes severe flickering and noise, and if left can cause overheating and fires.

These problems do not occur with most modern electronic starters. Electronic starters prolong lamp life (by 20% from 15,000 to 18,000 hours for T8 tubes, for example) and they last for up to 10 years. However, care should be taken in selecting these starters to ensure they ignite the fluorescent tube correctly. Some electronic starters are of inferior design and construction. 

Reflector

The most important element in a light fitting, apart from the lamp(s), is the reflector. Reflectors impact how much of a lamp’s light reaches and illuminates an area, as well as how that light is distributed. Reflectors are generally either diffuse (painted or powder coated white finish) or specular (polished or mirror-like). The degree of reflectance of the reflector material and the reflector’s shape directly influence the effectiveness and efficiency of the fitting.

Reflectance – Conventional diffuse reflectors have a reflectance of 70-80% when new. Newer high-reflectance or semi-diffuse materials have reflectances as high as 85%. Conventional diffusers absorb light and scatter it throughout the room, rather than reflecting it to the area required. Over time, reflectance values can decline due to the accumulation of dust and dirt on the diffuser, as well as yellowing caused by UV light.

Specular reflectors are much more effective in that they maximize optics and specular reflectivity, thus allowing more precise control of light and sharper cutoffs. In new-condition they have total reflectance values in the range of 85-96%. These values do not deteriorate as much as they do for conventional reflectors as they age. The most common materials used are anodized aluminum (85-90% reflectance) and silver film laminated to a metal substrate (91-95% reflectance). Enhanced (or coated) aluminum is used to a lesser extent (88-96% reflectance). If not designed and made properly, high reflectance reflectors can produce intense reflected images of the lamps at certain angles thus causing a distracting “flash” and unwanted discomfort arising from glare.

Reflector Shape – In conventional light fittings the reflector is simply the luminaire body painted gloss white, usually an open “box” shape. As about 70% of a tube’s light is emitted up or sideways, this causes multiple, random diffuse reflections resulting in high absorption losses and poor control. Modern, high efficiency luminaires use carefully designed geometric specular reflectors with a generally curved shape created by a number of flats and bends to approximate an ideal curved profile, so expertise in both the design and manufacture is essential to get maximum performance. These specular, purpose-designed reflectors give better directional control of the light output. They also reduce losses in any diffuser lens because of the reduced surface inter-reflection and absorption due to lower angles of incidence (i.e., most light directed downwards at the optimum exit angles).

In choosing a reflector and the required performance in a luminaire, the key factors to take into account are:

• Specular reflectance
• Light pattern distribution for uniformity of light (spacing ratio or SHR)
• Luminaire Light Output as a Coefficient of Utilization (max. UF value, not LOR)
• Reflector resistance to fluorescent tube UV damage
• Reflector surface depreciation rate over luminaire life
• Delamination and scratch resistance of reflector
• Resistance to dust build up, marking and the ease of cleaning
• Access to luminaire components.