Tear Down of A Popular Low Cost LED Low Bay
A few days ago, one of my customers came to my office with an LED low bay light sample he bought from Alibaba. He told me he was very much interested in this lamp because the price is extremely attractive. Based on trust, he asked me to take a look, hence our team conducted a disassembly experiment to see what’s inside of it. Meanwhile, as a professional LED manufacturer, we also hope you can get some ideas from this product review for selecting high quality LED bay lights.
It is a 30W LED low bay, usually used in locations of lower height. It is not a stranger to me, I have seen similar low bay LEDs in 2014 and I was told it has a huge sales volume, even today. This customer told me he bought it for 25 RMB last month (June of 2017). If the wattage is accurate, the cost per wattage is less than 1 RMB （merely 15 cent in US dollars I have to admit that Chinese LED manufacturers are awesome at producing cheap products).
My first impression is that it is an economic LED lamp, with very simple spec tag that indicates:
- Power: 30W
- Input: 220Vac 50-60Hz
Optical and Electronic Parameters of The LED Low Bay Light
First of all, we need to know the real optical and electronic parameters by putting it into the integration sphere, and we got this:
First, it is surprising to see the real wattage is 17.4W, only 60 percent of the nominal power.
Second, in today’s LED lighting technology, a luminous efficacy of 74.8lm/W is far from good enough.
Third, the PF value is 0.54, which is very low. It’s true that it is limited by the small size requirement of the LED driver, most of the LED light bulbs (light cup, bulb) below 5W cannot reach a high PF. But it is no longer a technical issue for LED lamps above 15W to reach a high PF value above 0.9. I believe it is more of cost concern to use a cheap driver solution.
Last but not least, the average color rendering index (CRI) of Ra 69.4 is usually not enough for a low bay. They differ from LED high bays, which don’t often require a high CRI. An LED low bay is usually used in commercial environments, such as a shopping mall or a fresh food supermarket. It works to increase sales and create a high quality service atmosphere, therefore CRI is critical. We notice that the R9 is -35 in the test report, which means this low bay is very poor at illuminating red objectives. However red is such an important color, especially in fruits, vegetables, meat and sea food shops. If this lamp is installed in these shops, the products will definitely become less attractive.
Next, we will tear it down and check it part by part.
Heat Sink & The Lamp Body
The heat sink is made of typical aluminum profile material. The diameter is about 9cm and the height is about 3cm, and there are 36 fins in total. If your math is good enough, you will know the surface area is about 400cm2. There is a useful formula to quickly estimate heat dissipation area:
Heat dissipation area = LED wattage x 25 cm2
It says that every 1 W LED chip will need about 25-30cm2 of aluminum material to take the heat away (it is an experience-based formula to roughly evaluate whether the heat dissipation area is sufficient for a specific heat sink, it only works on aluminum material). According to this formula, a 18W LED lamp will need at least 450 cm2, so it seems slightly insufficient, but we will verify it later.
The surface of the heat sink is oxidized, the cutting edge is chamfered as well to prevent cutting your hand. There’s not much burr to be seen, which means the raw material has been gone through a ‘caustic wash’ process to get a better surface (many cheap LED light heat sinks have neither been caustic washed nor chamfered to cut costs).
I have to say that the lamp shade is the most interesting part of the overall design. The lamp shade is made of oxidized aluminum material, too. It doesn’t look different from others. But when you take the diffuser off in the middle, you will find that the LED plate is fixed on the bottom of the lamp shade. This is totally different from most of the LED high/ low bay lights.
Normally the LED plate doesn’t have contact with the lamp shade directly, but is attached to the heat sink. The lamp shade is removable and is only used to shape the light beam. However, in this sample, the lamp shade is located between the LED plate and the heat sink. If we look at the heat conduction path, it is LED -lamp shade – heat sink. In other words, the lamp shade takes part in the heat conduction. We measured the size of lamp shade and calculated that the surface area of it is about 1200 cm2. This is considerably big for heat dissipation and will help to reduce the LED temperature greatly.
We noticed that the diffuser is attached with silicon glue. Of course, silicone glue can handle higher temperatures, but it will also very likely lose its stickiness over time, especially at high temperatures. For sure it is from cost cutting again but attaching mechanically (screws, fixing ring, etc.) is always a better solution.
After that, we lit it up for 30 minutes to wait for its thermal equilibrium state. Below is what we see from thermography.
The higher temperatures are in the driver chamber and LED plate, which is common sense. These are the major heat sources of almost all LED lights. We also notice that the lamp shade at high temperature, which means this special design works. The thermography proved our early judgment. The outside edge of the heat sink is blue, which means the heat sink is basically sufficient for this wattage. As thermal imaging only shows the heat distribution of the lamp surface, we need to obtain the real temperature of key positions. We use heat conductive glue and stick the temperature detecting lines to four key positions.
Below is the data:
|T2||LED soldering point||50.4℃|
The result is not bad, the temperatures are acceptable. The room temperature is 17.5℃, therefore the temperature rise is between 23-33 degree, which is pretty good. But remember, it is not 30W but 18W.
The LED Driver (Power Supply)
The E27 socket is connected to the heat sink by a plastic chamber where the driver is. We can observe that the driver is covered with a green insulation sheet to prevent direct contact between the driver and metal parts. The insulation sheet is hooped with a yellow tape, that’s all insulation treatment. This is a typical and a commonly seen insulation treatment in low cost LED lights. It is cheap, but unreliable because the insulation sheet will very likely slip off the tape. Many LED light manufacturers tend to exchange safety with low cost, but it is not worth doing so at all when taking the business’s reputation into consideration.
It is a constant current driver, but non-isolated. The driver is not big in size, with a very simple circuit. Basically，there’s one transformer on the PCB, and one piece of IC, few electronic capacitors and diodes, and the components do not look very nice, and therefore must not from big brand suppliers. One common issue for most non-isolated drivers is that they usually come with the higher output voltage and lower current because most of the electronic components are current-sensitive (or heat-sensitive) – higher current will lead to a higher temperature, and therefore, require a higher quality level, and thus , higher cost, and vice versa. The output voltage can often reach over 150 Volts （connecting 50 LEDs in one series will immediately exceed 150V） or even higher, substantially exceeding the safety level that human body can bear (36 Volts). A high voltage output driver with poor insulation is often fatal，especially when most of the LED lamp bodies are metal.
LED Light Source
LED is always the most sensitive part among all relevant components. There are 48 LEDs on the PCB. The LED size indicates that they are 5730 encapsulations, which are typically 0.5W per LED. But according to the test report, the whole lamp in only 18W, which means each LED is merely 0.375W, much lower than the rated power of a typical 5730 LED, therefore is technically quite enough to support this LED low bay light. But I’d like to make a note here that 5730 is not always 0.5W, it really depends on the chip size inside the encapsulation. The smaller the chip size, the lower the current it can handle and therefore the lower the power it can produce, which is cheaper, of course (it’s like you’re served a tiny beefsteak with a big plate in the restaurant). According to the print on the PCB, the LEDs are connected in 2 series and 24 parallel, which means they require a driver output of 25mA and DC72 Volt (to drive 18 Watt power), which verifies what I have explained about the non-isolated driver earlier.
By the above analysis, we had a basic comprehension that this LED low bay is generally low-end, it’s real power is only 60 percent of what it claimed, and cannot provide the illumination level that people would expect. Nevertheless, the heat dissipation design is pretty good and smart. The LED driver is of low quality and lacks basic intelligent protection and is a high safety risk. The system’s luminous efficacy is low, which will not save much electricity; the color quality is poor, cannot provide quality light in decent buildings. However, it can still be used in unimportant locations as it’s cheap enough.