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The Science of Fluorescent Lighting

How does a fluorescent lamp work?

How a Fluorescent Light Tube Works

The origin of the fluorescent tube dates back to 1938, when it became possible to produce radiation of visible wavelengths by exposing various phosphors to ultraviolet radiation.

The source of this UV was a glass tube with electrodes on each end and sealed. A small quantity of mercury is placed inside the tube along with inert gases. With the glass tube in a state of low vacuum pressure, the mercury vaporizes and acts as the conductor between both cathodes, creating a mercury vapor arc resulting in the release of UV radiation of 253.7 nanometres.

When a lamp of this design is produced with no phosphor coating, it produces a very small amount of violet light and is considered to be an ultraviolet lamp used for germicidal and sterilization purposes. It is harmful for humans to be exposed to this type of lamp. Another variation of this process is the tanning lamp, which is coated by phosphors that allow a high percentage of the UV produced to radiate through. These lamps are harmful if a person is exposed to them for more than the FDA has allowed.

It is important to note that the operation of a standard 40 watt lamp results in 60% of the energy being converted to UV radiation or approximately 24 watts. However, only 21% of this energy or 8.5 watts is transformed into light. The remaining 39% of the UV energy and a total of 77% of the total energy used by the lamp is transformed into heat, infrared and radiated energy. Only 23% of the total lamp wattage is actually transformed into visible spectrum or light.

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What are the different lamp diameters and base types?

Medium Bi-Pin (MBP)

Medium Bi-Pin (MBP) base is used for both T12 and T8 diameter tubes. Typically found on lamps from one foot through five feet in length.

Single Pin (SP) Slimline Lamp

Single Pin (SP) base is used on both T12 and T8 diameter fluorescent tubes. Also referred to as Slimline lamps. Typically found on lamps four feet through eight feet in length.

Recessed Double Contact (RDC) for HO lamps

Recessed Double Contact (RDC) base used primarily in high current output (HO) lamps for very cold operating environments. Typically found on lamps two feet through eight feet in length.

Tube Diameters


3/4 inch diameter

T = tubular shape, 6/8 = 3/4

T8 1 inch diameter T = tubular shape, 8/8 = 1
T12 1 1/2 inch diameter T = tubular shape, 12/8 = 1 1/2

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What is a ballast?

A ballast is required for use with gas discharge lamps such a fluorescent, to provide them with the necessary starting and operating electrical conditions. Once the arc has been struck and the fluorescent lamp is lit up, electrical resistance becomes negligible and the principal function of the ballast is to limit current to the lamp while it is operating.

All PROMOLUX fluorescent tubes are designed to function with industry standard ballasts. A ballast will have a label indicating the wiring configuration and lamp types that should be used with it. It is advisable to replace the ballast each time the lamp is replaced.

The Electronic Ballast and associated T8 fluorescent lamps have been legislated as the new standard in North America. This is due to national energy concerns, as well as concern for the environment. It is estimated that 2 million fluorescent tubes are thrown in the trash each day. The smaller diameter T8 lamps represent much less material such as glass, mercury, metal, etc.

Electronic Ballast

Electronic ballasts substitute solid state circuitry for some of the magnetic components used in conventional ballasts. An electronic ballast operates compatible fluorescent lamps at a higher frequency then the 60 hertz (available from utility) to improve performance and efficiency.

Preheat Ballast

Typically used with short length T8 and European T8 lamps.

Rapid Start Ballast

Typically used with T12 MBP base lamps up to 48" in length.

Instant Start Ballast

Typically used for single pin slimline T12 and T8 lamps.

High Output Ballast

Typically used for all high current output (HO) lamps with RDC base.

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