A halogen lamp is a type of incandescent lamp with a fraction of halogen gas in it. It operates on the principle of the halogen cycle. It can be an AC or DC and are available in various shapes and sizes. Due to its wide range of sizes and variations, it has been widely used in a number of applications. For example, in the house, it is useful to light up the rooms. In medical equipment such as the microscope, colorimeter, clinical chemistry analyzer, etc, it is useful to carry on the tests. It is also used in film projectors, scientific equipment, etc. Thus, today we will discuss the construction and working of this lamp. Besides that, we will also discuss the advantages, disadvantages, handling, and testing methods of the halogen lamp.
Halogen lamp consists of a tungsten filament. This filament is very thin and compactly arranged inside the quartz envelope. The inert gas such as argon fills up the major portion of the lamp. Along with this, a trace amount of halogen gases such are iodine and bromine are present inside the lamp.
When the current flows through an extremely thin tungsten filament heat is produced. This rise in the temperature of the filament causes the emission of light (white or yellow). Due to extremely high-temperature evaporation of the tungsten takes place. Novel gases help to reduce the rate of evaporation of the tungsten. In the case of a normal incandescent lamp, this tungsten gets adhered to the wall of the glass covering. But, in the case of a halogen lamp, the tungsten combines with the halogen gas. So, it prevents the blackening of the lamp.
As the halogen gas is in continuous motion, it comes in contact with the filament. Thus, the tungsten combined with the gas can return to the filament. So, this process of bringing the evaporated tungsten back to the filament by the halogen gas is known as the halogen cycle. This cycle increases the life span of the lamp and maintains the proper light transmission.
Advantages of Halogen Lamp
- The lifespan of a halogen lamp is about 2000 hours in an ideal case. This is more than that of a regular incandescent lamp.
- It does not take much time to startup.
- The halogen gas present in the lamp does not allow the tungsten to adhere to the wall of the lamp. Thus it prevents the blackening of the lamp.
- It has got a compact size in comparison to other light sources. Thus, it is more convenient to use.
- It has got a higher efficiency in comparison to other incandescent lights.
Disadvantages of Halogen Lamp
- The efficiency of the halogen lamp is not more than 10 to 30%. That means, out of the total energy only 10 to 30% converts into light energy. And the remaining energy converts into heat energy.
- The filament of the lamp is extremely hot. (around 3000 K). So, if anyone touches the bulb, there can be a high chance of skin burn.
First thing is that do not touch the head of the halogen lamp when it is in use. Else, you may experience a skin burn. Second thing is that you need to know the rating of your lamp before use. For example, in a compound microscope, if you are using a low voltage 6 VDC lamp instead of 12 VDC, then the lamp will not emit sufficient light. Thus, the lamp will emit a yellow color light. So, it will be difficult to observe the slide.
Testing of Halogen Lamp
Take a multimeter. Then set it in a diode or continuity mode. After that check the continuity at the two points of the pin. If there is continuity between the two points then, the lamp is ok. Else, it can be defective.
The other way to test the lamp is to manually inspect the filament. If it is damaged, then there can be breakage along the path of the filament.
You can also supply the necessary voltage and verify the condition of the halogen lamp.
Replacing a Halogen Lamp in a Semi-auto Biochemistry Analyzer
Remove the old halogen lamp with a new one. After that adjust the lamp.
For the adjustment of the lamp, you need the absorbance (optical density) test. On the display board, you will see the absorbance of the water. The permissible value of the absorbance is between 2500 to 3900. Now, tighten or loosen the adjustable screws to adjust the absorbance of the water. When the permissible absorbance is reached, tighten the fixing screw completely.
Even though the above method is mentioned in most of the user manuals, it is a quite difficult task to perform. . This is because once the machine starts to get old the absorbance will start to decrease. It might even reach 800 after a few years. So, in that case, you need to replace your photo-detector or simply change the machine. Also, even if the absorbance decreases, you will generally be able to get a good result.
The main concept of adjusting the lamp is to allow more light to pass through the window of the flowcell. But, in different models of the analyzer, you may not have this feature.