Dear Sudeep,

which is the purpose do you need a lamp dimmer for? Water treatment/disinfection? Which kind of lamp would you like to use? Halogen, incandescence, ...

Here you can find an example and some information.

http://www.phason.ca/programmable-lighting-control-1.htm

http://www.phason.ca/pdfs/plccase-ac.pdf

Cheers

Valerio

First answer appropriate in questioning intended result.  Some lamp types cannot be dimmed without effects and are designed to operate at full current.  I do not know for this example.  If you want less intensity you might try increased distance of lamp to work area or adding some filter or shade to reduce intensity.  It would be good to discuss this as well as your intended result with the lamp company and/or manufacturer. 

@Valerio Silli & William F. Hansen

Thank you for your prompt response.

Here are some more details regarding my project.

As i have previously mentioned, am working on Ballast Water Management System which involves a UV sterilization(inactivation) unit.

Am Planning to use a Medium Pressure Mercury Lamp (germicidal) to produce UV-C radiations which will act on the microorganisms and inactivate them.

The Purpose of lamp dimming is to control the intensity of light which in-turn decreases the consumption of electric power.

As we are dealing with random sea water, the transmittance of UV may vary from place to place and also the transmittance will decrease as the water is more turbid.

Intensity of the lamp is to be Increased when the water is turbid and Decreased when its clear.

A PLC(Programmable logic controller) will be used to control the whole system (including the Water Flow, Mechanical filter unit, sensors and the UV reactor unit).

So am planning to use the same PLC to control the Intensity of UV Lamp(Medium Pressure Mercury Lamp).

Therefore am asking that do i need to use any lamp driver for the purpose or any electronic ballast (which can be interfaced with PLC) will do this for me?

Dear Sudeep,

as I understand, your need is to apply the UV properties to disrupt  the DNA of microorganisms in the ballast water. In this system you need a tool to detect the turbidity of the water because the intensity of the UV radiation have to be proportional to the this factor to ensure sterilization. So you should connect a light sensor (transmitter and receiver) to a input channel of the PLC, in order to assess the water "transmittance", another feedback channel of the PLC will control directly or by another driver (appropriately calibrated) the power supply of the lamp (and so its intensity). The problems may be that all the system should be waterproof, but especially that some type of lamps do not allow to control intensity by varying current, voltage, or phase. So you have to think to some lamp type that has this feature, for example a LED or incandescence lamp in which the intensity is simply controlled by voltage or current . Unfortunately I'm not a technical, but I suppose that you could find some of appropriate in the specific UV light sector.

Regards Valerio

It would be simpler to adapt the UV dose to the water quality by changing the flowrate through the disinfection reactor. Pump speed can be adjusted by frequency modification which is very simple and the electronics is inexpensive compared to modulation of the UV lamps.

Adjusting the output of a medium Pressure Mercury Lamp is possible down to about 20-30 % of the design output.

I agree with professor Andersen, 

Also you can see the problem from another angle. You can split the total Irradiation (Watts) at a larger number of lamps instead of 1 and to on/of different number of lamps depending on the intensity that you need every time .... 

(maybe you must model the distribution of light inside the reactor with this solution)

if you just adjust the Watts i believe that you may reduce significant the lamp life