A brief discussion on the advantages and costs of built-in LED fluorescent lamps

At present, almost all LED fluorescent lamps on the market use built-in power supplies. The so-called built-in type means that the power supply can be placed inside the lamp tube. The biggest advantage of this built-in type is that it can be made to directly replace the existing fluorescent lamp tube without making any changes to the original circuit. Therefore, the shape of the built-in power supply is usually made into a long strip so that it can be stuffed into the semi-circular lamp tube. There are two types of built-in power supplies, one is non-isolated (Figure 1) and the other is isolated (Figure 2).

Non-isolation means that there is a direct connection between the LED load and the 220V input, so there is a risk of electric shock if you touch the load. There is only a very thin insulation layer of the aluminum substrate between the 220V and the aluminum shell, which is usually not easy to pass CE and UL certification.

 

Isolation means that there is an isolation transformer between the input and output ends. This transformer may be power frequency or high frequency. But it can isolate the input and output. It can avoid the risk of electric shock. It is also easy to pass CE or UL certification.

1. Power consumption of LED fluorescent lamp with built-in power supply

The biggest advantage of using a built-in power supply is that it can directly replace existing fluorescent lamps without making any changes to the original wiring. So does this advantage of the built-in type also come at a price? Indeed, it is, and the price is not small. This starts with the ballast structure of ordinary fluorescent lamps:

 

We know that the most common fluorescent lamp uses a series iron core inductor and a parallel starter (Figure 3a) to start the lamp. When replacing this circuit with an LED fluorescent lamp, just unplug the starter. However, since the iron core inductor is still connected in series in the circuit, it still causes a loss of nearly 6.4W (Philip) to 10W (domestic). As a result, the extra loss greatly reduces the energy saving effect of the LED. For example, a 20W LED fluorescent lamp can replace a 36W fluorescent lamp. Taking a built-in non-isolated 20W LED fluorescent lamp as an example, the actual test results are as follows.

 

 

In other words, the result of direct replacement is a significant reduction in efficiency. For domestic inductive ballasts, the efficiency is only 56.2%, which only saves 6.8W of electricity compared to ordinary fluorescent lamps.

This greatly reduces the energy-saving performance of LED fluorescent lamps, making it difficult to implement energy management contract (EMC).

2. Heat dissipation and lifespan

Another major disadvantage of the built-in power supply is its low lifespan. Because the power supply must be placed in an aluminum tube, the aluminum tube cannot be made into a fin shape, but can only be an ordinary semi-cylindrical shape, with some shallow strip grooves on the surface at most (Figure 4).

 

The surface area of ​​this semi-cylinder is: 2πR*h/2=πR*h. For a T8 tube, its diameter is 26mm, so the radius is 13mm. The surface area of ​​a 1.2-meter T8 tube is: π*1.3+120=490cm2. We know that the surface area of ​​an LED heat sink is usually required to be 60cm2/W. Therefore, this semi-aluminum tube can only dissipate about 8W of heat. The input power of a T8 LED fluorescent lamp is usually 20W. Assuming that the luminous efficiency of the LED is only 20%, 16W of the input power will become heat. Now only 8W of heat can be dissipated, and there is still 8W of heat that cannot be dissipated. As a result, the junction temperature of the LED increases and the life is shortened.

Moreover, since the power supply is built-in, the heat of the power supply is also added to the tube. Assuming the efficiency of the power supply is 88%, 2.4W of heat must be dissipated, which is equivalent to an increase of 30% of the heat. In other words, a total of 10.4W of power cannot be dissipated. This makes the heat dissipation of the LED more difficult, or in other words, the service life of the LED is further shortened. Moreover, the length of the power supply is about one-fifth of the length of the lamp tube, and the heat generated by the power supply is also concentrated in this section, so that the LEDs close to the power supply are baked more hot, and thus the life is shorter than the LEDs in other places. When the lamp tube is damaged, the section close to the power supply will go black first. It can be considered that the life of the LED fluorescent lamp with a built-in power supply will not exceed 10,000 hours.

Moreover, when the power supply is placed inside the tube, the power supply itself has to withstand the very high ambient temperature generated by the LED, which greatly reduces the life of the electrolytic capacitor in the power supply and thus reduces the life of the entire lamp.

3. Cost of Use

Because the life of LED fluorescent lamps with built-in power supply is only 10,000 hours, compared with 50,000 hours of external power supply, its use cost is obviously 5 times higher. Moreover, during use, whether the LED or the power supply is damaged, usually both must be discarded together. However, LED fluorescent lamps with external power supply can be discarded whichever one is damaged.

In addition, the built-in power supply also increases the cost of recycling electronic waste because the power supply must be disassembled and processed separately.

4. Other functions

The external power supply is not only highly efficient and has a long life, but also has special functions such as manual dimming or automatic dimming, which are unmatched by the built-in type!