The difference between LED light source and LED lamp efficiency

LED has entered new markets and its application areas are expanding. It has been widely used in traffic lights, display screens, landscape lighting and decorative lighting, etc. Its market share in the backlight field has also gradually increased. Many companies that used to produce traditional light sources have also launched LED projects. Industrial investment continues to heat up, and the record of light efficiency has been repeatedly refreshed. Recently, Cree, an American company, announced that its white power LED light efficiency has once again broken the industry record. The laboratory parameter has reached 231 lm/W, which is more than doubled compared with the 100 lm/W of white LED announced by Nichia Chemical in June 2006. It is believed that with the advancement of technology, this record will be broken.

As the concept of light efficiency is also applied to LED lamps, many LED lamps have also joined the light efficiency competition. Manufacturers are ignoring the difference in product functions between LED light sources and LED lamps, and only use light efficiency as a benchmark for lamp performance. They simply pursue high light efficiency indicators and ignore the reliability, color quality, visual comfort and other characteristics that LED lamps should meet as a system. As a result, the pursuit of light efficiency is prevalent in the domestic LED lighting market. The so-called "high-efficiency LED lamps" used in municipal engineering and semiconductor lighting pilot demonstration projects often fail to achieve their expected energy-saving and emission-reduction purposes, resulting in greater negative effects.

In view of the current lighting market situation, this article explains the difference between LED light sources and LED lamp efficiencies. It reveals the reason why the trend of chasing light efficiency has spread from LED light sources to LED lamps. It emphasizes that the lamp efficiency of LED lamp products should be coordinated with other performance requirements, and the lamp efficiency should be based on meeting the various performance requirements of LED lamps.

1. Light efficiency is a classic performance indicator of light source products

As far as light sources are concerned, light efficiency is a classic indicator. The emergence of each new light source is directly related to the higher light efficiency it achieves. In this way, light efficiency has become an important indicator of the performance of LED light sources without exception. Of course, other performance indicators of light sources include color rendering index, chromaticity coordinates, color temperature and lifespan, etc.

For lamps using traditional light sources, the light output rate, that is, the ability of the lamp to convert the light flux of the light source, is a classic indicator of lamp performance. Since the performance parameters of LED light sources have not yet reached the level of standardization, and the LED light sources used in many lamps are irreplaceable, the concept of light efficiency has also been applied to LED lamp products.

2. The efficiency of LED lamps is different from the efficiency of LED light sources

When both LED light sources and LED lamps use luminous efficacy as a performance evaluation indicator, we first analyze the connotations and differences between the two to understand the performance of LED lamps, and use the correct terms to evaluate the luminous efficacy of LED light sources and the effectiveness of LED lamps.

1. The concept of LED light source efficiency and LED lamp efficiency

The luminous efficacy of a LED source is defined as the ratio of the luminous flux emitted by the light source to the electrical power consumed.

The definition of LED luminaire efficacy is the ratio of the initial total luminous flux emitted by the luminaire to the power consumed under the luminaire's claimed conditions of use, with the unit of lm/W.

"Luminous efficiency" is used to evaluate LED light sources, and "efficiency" is used to evaluate LED lamps. Both the luminous efficiency of LED light sources and the efficiency of LED lamps indicate the efficiency of converting electrical energy into light energy. They are indicators that describe the energy-saving characteristics of lighting products, but their connotations are different.

2. Different luminous flux

The luminous flux of the light source in the LED light source light effect refers to the luminous flux emitted by the bare light source (not yet installed in the lamp). The LED light source can be an integrated LED lamp or an integrated LED module, a semi-integrated LED lamp or a semi-integrated LED module, or a non-integrated LED lamp or a non-integrated LED module.

The molecular luminous flux in the LED lamp efficacy refers to the luminous flux emitted by the lamp after the light source is installed in the lamp and the required LED control device or power supply of the LED control device is used. The LED control device or the power supply of the LED control device can be integral, built-in or independent. Lamps using LED light sources may use reflectors and diffusers.

The light source installed in the lamp may be a single light source or a collection of multiple light sources, but due to the efficiency loss caused by the interaction of thermal energy and electrical energy, as well as the efficiency of the lamp's optical system, the luminous flux of the LED lamp is not equal to the luminous flux of the LED light source or its simple accumulation.

The measurement states of the luminous flux in the LED light source luminous efficiency and the luminous flux in the lamp efficacy are different. The former is measured in the pulse state, and the latter is measured in the steady state.

The light in the LED light source effect is non-directional, as long as the light can be emitted, it doesn’t matter where it is. However, the light in the LED lamp efficiency is directional, and the light needs to be emitted to a useful area.

When using the same LED light source, the luminous flux of the LED lamp is smaller than the luminous flux of the LED light source.

3. Different input power

The denominator in the LED light source efficacy is also different from the denominator in the LED lamp efficiency. For example, for non-integrated LED modules, the power consumed by the LED light source refers only to the power consumed by the LED module, excluding the power consumed by the LED control device. The power consumed in the LED lamp efficiency refers to the input power of the lamp, including not only the LED light source but also the power consumed by the LED control device. The power consumed by the LED lamp is greater than the power consumed by the LED light source.

4. The relationship between LED lamp efficiency and LED light source efficiency

Due to the different ranges of luminous flux and electrical power involved, the luminous efficiency of LED light sources is different from the efficacy of LED lamps, and the luminous efficiency of light sources is much greater than the efficacy of lamps. First, after the LED enters the lamp, the junction temperature rises and the light output decreases (heat loss); second, the system loss exists after the light source enters the lamp and uses the LED control device or its power supply; third, the loss of light after passing through the optical system of the lamp, that is, the lamp efficiency (light loss).

Lamp efficiency = light source efficiency × (1-heat loss after entering the lamp)% × (1-system loss) × (1-light loss after entering the lamp)%

From the above analysis, it can be seen that the light effect of light source and the efficiency of lamps are completely different and cannot be confused.

3. LED light sources start a light efficiency competition, and the trend of chasing light efficiency spreads from LED light sources to LED lamps

As LED lighting efficiency records are constantly being refreshed, the LED lighting efficiency competition that is spreading has the following misunderstandings:

1. Only improve the lighting effect, not the color temperature and color rendering index

It should be pointed out that the lighting effect at a certain color temperature CCT and a certain color rendering index Ra. For the same lighting effect, low color temperature is obviously much more difficult than high color temperature.

The US Energy Star requirement for correlated color temperature of solid-state lighting indoor lamps is: it should be one of the following nominal correlated color temperatures (CCT): 2700K, 3000K, 3500K, 4000K, 5000K (only for commercial use). Energy Star does not allow solid-state lighting indoor lamps: 5700K, 6500K color temperature.

2. Only improve lighting efficiency, not lighting comfort

When the trend of lighting efficiency competition spread from light sources to lamps, another phenomenon of blindly pursuing lamp efficiency was that the anti-glare diffuser was omitted, the comfort of the lamp was ignored, and glare control was not considered.

3. Only mentioning lighting effect, not reliability

In order to blindly pursue the efficiency of lamps, the protective covers that should be added to outdoor lamps are omitted, exposing parts that should not be exposed and ignoring the reliability of LED lamps.

4. LED lamps generally have low power and high luminous flux markings

Since it is related to efficiency, we paid attention to the deviation between the input power and rated luminous flux marked on 276 LED downlight products and the actual measured values, and found that the phenomenon of low power and high luminous flux is common. This deviation will lead to the product's "light efficiency" being artificially high, pushing up the actual level of LED lamp efficiency.

1. Low power and high luminous flux

The input power of LED lamps is the denominator in the product efficiency calculation formula. When the luminous flux is the same, the lower the input power, the higher the product efficiency. Reducing the input power of the product can improve the product efficiency. When marking the product characteristics, there may be a phenomenon of marking the power as low as possible.

The input power of the LED lamp can be obtained through actual measurement, and the percentage of the input power marked on the lamp can be calculated using formula (1). We can then obtain the deviation ηP between the measured power and the nominal input power.

ηP=(measured power/nominal power)*100% (1)

The significance of the calculation results:

-ηP=100%, the measured power is consistent with the nominal value, and there is no deviation from the nominal value.

-ηP<100%, the measured power is less than the nominal value, and the nominal value is too high.

-ηP>100%, the measured power is greater than the nominal value, and the nominal value is lower.

A lower nominal input power value will result in a higher calculated LED downlight efficacy.

In order to intuitively understand the distribution of the entire sample, we use a scatter plot to intuitively represent the measured data of 276 lamps, as shown in Figure 1.

Figure 1 Scatter plot of the deviation (%) between the measured power and the nominal power

As can be seen from Figure 1, the data are mainly distributed in the range of 90% to 120%. If the allowable deviation limit between the actual power and the rated power is specified, the corresponding data of the deviation pass rate can be found in Table 1.

Table 1 Qualified rate data for different deviation limits

From the analysis of Table 1, we can see that:

In Table 1, ηP<100%, that is, there are 114 samples with actual measured power less than the nominal power, ηP=100%, that is, there are 2 samples with actual measured power equal to the nominal power, and ηP>100%, that is, there are 160 samples with actual measured power greater than the nominal power and lower nominal power, accounting for 57.98% of the total. This shows that there are a large number of samples with low power standards and misleading consumers in the market.

If a 10% under-standard power is allowed, that is, the deviation calculated according to formula (1) is ≤110% as the deviation limit, 46 lamps will exceed the allowable deviation, and the unqualified rate among the 276 groups of lamps is 16.7%.

2. Luminous flux

The luminous flux of LED lamps is the numerator in the product efficiency calculation formula. At the same input power, a higher luminous flux indicates a higher product efficiency. Increasing the luminous flux of a product can improve the product efficiency. When marking product characteristics, the luminous flux may be marked as high as possible.

The luminous flux of the LED lamp can be obtained through actual measurement, and the percentage of the rated luminous flux marked on the lamp can be calculated using formula (2). We can then obtain the deviation ηL between the measured luminous flux and the rated luminous flux, as shown in formula 2:

ηL=(measured luminous flux/rated luminous flux)*100% (2)

The significance of the calculation results:

-ηL=100%, the measured luminous flux is consistent with the nominal value, and there is no deviation from the nominal value.

-ηL<100%, the measured luminous flux is less than the nominal value, and the nominal value is too high.

-ηL>100%, the measured luminous flux is greater than the nominal value, and the nominal value is lower.

A higher nominal value of the rated luminous flux will result in a higher calculated LED luminaire efficacy.

In order to intuitively understand the distribution of the entire sample, we use a scatter plot to intuitively represent the measured data of 276 lamps, as shown in Figure 1.

Luminous flux is an important indicator for evaluating the performance of LED downlights. The higher the rated luminous flux, the higher the luminous flux can be obtained under the same power. In order to sell better products, some manufacturers will set a high rated luminous flux. In order to intuitively understand the distribution of the entire sample, Figure 2 shows a percentage scatter plot of the measured luminous flux and the rated luminous flux.

Figure 2 Scatter plot of the ratio of measured luminous flux to nominal luminous flux

As can be seen from Figure 2, the data ranges from 40% to 140%, which is quite scattered, indicating that the actual measured luminous flux deviates greatly from the rated luminous flux.

If the allowable deviation limit between the actual luminous flux and the rated luminous flux is specified, the corresponding data of the deviation pass rate can be found in Table 2.

Table 2 Qualified data of initial luminous flux at different deviation limits

From analyzing Table 2, we can see that:

If the luminous flux is allowed to be 10% higher than the standard, that is, the deviation calculated according to formula (2) is ≥90% as the deviation limit, 91 of them fall within the range of <90%, exceeding the allowable deviation. Among the 276 groups of lamps, the unqualified rate is 33.0%.

In Table 2, ηL<100%, that is, there are 160 samples with measured luminous flux less than the nominal luminous flux, accounting for 57.97% of the total. This shows that the actual measured luminous flux of most LED downlights is less than the nominal rated luminous flux. At present, there is a phenomenon of high rated luminous flux in the LED downlights on the market, which will mislead consumers and cause market confusion.

3. Actual performance level of LED downlights

Taking the measured LED downlight "efficiency" as an example, Figure 1 shows a scatter plot of the efficiencies of 276 downlights calculated after actual measurement. As can be seen from Figure 3, most of the data sets are concentrated in the range of 30 to 80, and only a few are greater than 80.

Figure 3 Scatter plot of measured performance

"Efficacy" is an energy-saving evaluation parameter for LED lamps. Table 3 gives the pass rate under different efficacy (LE) limits.

Table 3 Qualified rate of measured performance at different limits

As can be seen from Table 3, as the potency limit increases, the proportion of products that meet the requirements decreases. When the potency limit is 60, the samples that meet the requirements account for 55.43% of the total number of samples; and when the potency limit is 80, the samples that meet the requirements account for only 3.26% of the total number of samples.

If the requirement of 80% of products being qualified is followed, the current efficiency level is only around 40lm/W, which is obviously at odds with the energy-saving and high-efficiency characteristics claimed by LED lighting products. The actual measured "efficiency" of LED downlights is not as high as advertised by manufacturers.

Lamp efficacy is one of the performance requirements, which is constrained by other performance requirements, such as glare control (comfort of ambient brightness during use), reliability, IP protection level, etc.

We cannot blindly pursue high "light efficiency" and ignore the comfort and reliability of lighting. When other parameters that affect the use are taken into consideration, such as light color, color rendering, lighting comfort and product reliability, the efficiency of the lamp will be reduced.

Taking the luminous efficacy of a non-integrated LED module with a luminous efficacy of 80 lm/W as an example, the heat loss after entering the lamp is 25%, the light loss is 20%, and the system loss is 15%. The efficiency of the LED downlight = 80 lm/W × 75% × 80% × 85% = 40.8 lm/W (see Figure 4 for a schematic diagram).

Figure 4 Schematic diagram of LED downlight efficiency and LED light source light efficiency

4. Product performance that meets Energy Star standards

Energy Star's requirement for the efficacy of residential or commercial solid-state lighting downlights is 42 lm/W. An example of the efficacy, protection angle, correlated color temperature (CCT) and color rendering index (CRI) of an LED downlight that has passed the US Energy Star is shown in Table 4.

Table 4 Examples of LED downlight efficacy, protection angle, CCT and CRI in the United States

5. Explore the reasons for chasing light effects

The trend of chasing light effects has spread from LED light sources to LED lamps for the following reasons:

For a long time, LED downlights and LED streetlights have been mistakenly regarded as LED light sources, and the technical requirements or specifications formulated are similar to the performance requirements of LED modules. This is mainly caused by confusing the performance of LED lamps with that of LED lights.

In general, "lamp" refers to the light source. Various types of lamps are named according to the physical principle of light emission, such as incandescent lamp, high pressure sodium lamp, metal halide lamp, fluorescent lamp, ultraviolet lamp, electroluminescent lamp, tungsten halogen lamp, etc. The naming and classification of lamps have nothing to do with the place of application or the type of lamp used. "Lamp" refers to the lighting device, which includes the accessories and circuits required to light the light source, the optical components that redistribute the light emitted by the light source to meet the application requirements, and the assembly of components required for the installation, fixing and adjustment of the lamp. The classification and naming of lamps are related to their installation method or the place or purpose of their design and use, such as fixed ceiling lamps, movable table lamps, movable floor lamps, road lighting lamps, tunnel lighting lamps, garden lamps, floodlights and emergency lighting lamps, etc.

The term "lamp" is sometimes also used for certain types of lighting. Perhaps due to habit, many people call "road lighting fixtures" "street lamps" and "ceiling surface mounted lamps" "ceiling lamps". However, street lamps and ceiling lamps here do not refer to light sources, but to road lighting fixtures and ceiling surface mounted lamps. Similarly, "recessed or fixed downlight fixtures" are called "downlights", "portable table lamps" are called "table lamps", "portable floor lamps" are called "floor lamps", and "portable portable lamps" are called "portable lamps".

When people pick up an LED lamp, they are used to asking about the "light efficiency", as if "light efficiency" is the only indicator. Using "light efficiency" as a marketing indicator for LED lamps is not comprehensive. In essence, it is mistaking it for an LED light source, which is a substitution of concepts.

6. The standardization of performance indicators of LED lighting products in my country is on the right track

Internationally, IEC TC34 has made it clear that these LED lamps are included in the standard scope of lamp products. It should be said that the country has begun to reverse this orientation. The National Technical Committee for Standardization of Lighting Appliances has recently put the two national standards "LED Downlight Performance Requirements" and "LED Downlight Performance Requirements Measurement Method" under the jurisdiction of the National Technical Committee for Standardization of Lighting Appliances' Lighting Sub-Technical Committee. This is a good start, which is conducive to international integration and helps LED lamp manufacturers avoid detours.

At the same time, the lighting efficiency of LED downlights should be coordinated with other performance requirements.

The lamp efficiency of LED downlights is only one of many performance requirements. Attention should be paid to comprehensive development and should meet all performance requirements for downlights, including photometry, glare control, chromaticity, structure, thermal testing, reliability, low temperature, electrical properties, and classification.

VII. Conclusion

LED light efficiency and LED lamp efficiency are different and cannot be confused. LED light efficiency may be a relatively simple indicator of light source, but LED lamp efficiency is one of many performance requirements. It is constrained by other performance requirements. Various performance indicators should be coordinated and consistent. We cannot pursue LED lamp efficiency alone, and we should not sacrifice lighting environment comfort, reliability and other indicators as a prerequisite.