Wednesday, February 17, 2010

Bare fluorescent light pictures

This post contains a few pictures of bare fluorescent lighting as part of a series of posts on pictures of basic components of electrical systems. These series of short posts will be part of the building blocks that can help me present materials so they are easily digestible by beginners in electrical works.

Picture 1 – Normal view of 4-ft inch diameter bare-channel fluorescent light fixture

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Bare channel (Picture 1 above) fluorescent light fixtures has been one of the most low cost and energy efficient type of lighting that is available today.

The above picture shows an example of a bare channel fluorescent light fixture. This one was installed inside a substation room. That is why you can see that the wiring conduit is run on surface of the wall instead of concealed into the concrete wall.

However, the above light fixture does not have the fluorescent tube installed. The electrical substation is still under construction. Many workers were still in and out of the place. Lighting lamps and tubes were one of the most frequently stolen items at a construction site. It is for that reason that they are usually not installed until just before the commissioning stage of the installation works.

Picture 2 below had the fluorescent tube on. But the fixture is inside the Sample Room of the project.

The picture was taken during materials inspection of some of the fixtures. I was checking on the components of the light fixture. You can below a few other pictures that show the components of the light fitting.

The light fitting in Picture 2 is a slightly different type than that in Picture 1.

In Picture 1, the fixture is a bare channel type. The fluorescent tube is just exposed. It is a very efficient type of lighting assembly.

While in Picture 2, the fitting is provided with a wire guard. Other than that, it is almost the same design.

This type of design is usually installed at locations where theft of the fluorescent tube and vandalism of likely, such as at unprotected public corridors.

Picture 2 – Bare-channel fluorescent light fixture with wire guard

If you look closely there are more than one type of light fittings in the picture. They are all the fluorescent types.

Picture 3 – The fluorescent ballast

This is a 36-watt low loss fluorescent ballast.

You can also see painted onto the body of the ballast how it should be connected in the fluorescent light internal circuitry.

I will send a post how the fluorescent lighting works with detail descriptions on the operations of the internal circuitry. There are actually a number of variations to the basic circuitry that you see painted there.

Picture 4 – 240 volt fluorescent starter unit

This is the automatic fluorescent starter unit. The fluorescent lighting is an electronic device. The starter provides a short circuit to cause a high current to flow in the ballast coil of Picture 3 above.

The high current heats up the filaments at both ends of the fluorescent tube. The heated filaments release electrons into the lamp tube.

The starter unit is actually an automatic bimetallic heat switch. After a few seconds at most, the starter switch open-circuit, stopping the current flow through the ballast coil.

A strong magnetic field is developed in the iron core of the ballast coil due the high current flow.

When the current flow suddenly stops, energy of the magnetic field turns the coil into a source of electric voltage. Actually, the voltage developed there can be a few thousands of volts.

This high voltage, with the connections as painted on the ballast body, causes the gases inside the fluorescent tube in to break down and become a conductor.

As explained above, the operation of a fluorescent lighting uses a ballast coil in order to create a high voltage to break the gases in the tube into a conductor.

However, the strong magnetic coil also presents a very high inductive effect into the electricity supply circuit.

Due to this inductive effect, the current in the wiring becomes higher than the actual consumption of the light fixture.

This is what is called “low power factor”, or simply low PF.

Where many of these light fixtures are used, such as in large hospitals which has thousands of lights turned on simultaneously day and night, the difference between the total current drawn by the lights and the actual power rating can be hundreds of amperes.

Many electrical cables and equipment need to be sized much bigger, and therefore much more expensive, because of this simple reason.

More than that, the electricity supply authority would penalize an installation that has a low PF. That is because their cabling and equipment also need to be sized bigger.

In order to avoid all these problems, a device to turn the fluorescent lighting fixture from low PF to a higher PF is installed.

It is called “power factor correction” capacitor, or PF capacitor. Picture 5 below show the one installed inside all the fluorescent lighting in this project.

Picture 5 – Power factor correction capacitor

This blog is for beginners. I try as best as I can to turn complicated electrical subjects into easily digestible chunks of general knowledge. That is the highest objective of this blog.

However, it is not always easy to convert a highly technical subject such as this one into a general knowledge that is practically useful to everyone.

Therefore, every post that I send here will evolve as I constantly modify them and build them up in order to achieve this objective.

If there is anything that you would like me to explain sooner, that please do leave a comment. I may make your question a priority topic for my future posts.

See you in the next post.

(Lee Wan Seng)

Copyright Bare fluorescent light pictures

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