How to Convert Halogen Table Lamp into LED Light Source

According to the estimation of the International Energy Agency, more than 19% of the global power demand is used for lighting. Therefore, efforts are being made around the world to replace inefficient incandescent light sources with more efficient solutions.

At the consumer level, the focus of curbing power demand has been to promote the use of compact fluorescent lamps (CFL). The choice to use CFL is not without results; Each bulb contains mercury, which, if not handled properly, will eventually enter the landfill. In addition, the overall dimensions are not applicable to all lighting applications. An alternative that has attracted much attention is phosphor converted "white" LEDs. Led lumen output and efficacy - Measurement of lumen output and input power - continue to make significant progress year by year, while the lumen / dollar cost is declining. In addition to energy saving, high brightness LEDs can have a service life of more than 50000 hours when properly designed and operated, eliminating the cost of replacing bulbs.

Ready made halogen table lamps were used as the basis for the demonstration. The real world performance of the latest LED light source. Using creexlamp ® MC-E LED as light source. The product integrates four LEDs in a compact package, which is very suitable for directional lighting applications such as MR-16 and portable work lights. The original lamps were characterized before and after modification to highlight the performance differences in the real world.

Figure 1: ready made 50 W halogen portable table lamp.

Figure 2: 50 W bulb in bulb housing with protective glass cover and handle.

Figure 3: 60 Hz core transformer, 2.4 pounds.

Doe energy star standard lamps for solid-state lighting (version 1.1 - 12 / 19 / 08) include the requirement that the minimum power factor (PF) of portable residential table lamps is 0.7. Typical LED drivers at this power level typically have a PF of 0.5-0.6, lower than required. The solutions presented here are specifically designed to go beyond residential EnergyStar ® Pf requires no additional circuits.

Halogen incandescent bulbs usually work at a temperature of 250-350 º C. Therefore, the lamps must provide safety protection for users. In this case, the glass cover plate restricts access to the bulb to protect the user, and the plastic housing provides a heat shield above the bulb. Even with these safety measures, this halogen lamp also includes a rod end handle, so that users can safely aim at the lamp. Glass is special because it combines a filter to reduce unnecessary ultraviolet rays produced by halogen bulbs. The typical 12 volt halogen bulb used in these table lamps has an efficiency range of 14 to 18 LM / W. please note that as shown in Figure 3, this is only the rated efficiency of the bulb and does not include lamp loss or transformer loss at the bottom of the lamp holder.

High brightness LEDs show significantly higher light conversion efficiency, resulting in less waste heat for a given light output. Less waste heat means that the lamp assembly operates colder and does not expose the user to dangerous high temperatures. The bulb assembly has been redesigned and the heat sink (Figure 4) is installed in the existing plastic housing of the bulb fixture. The cast aluminum insert shown below is installed in the lamp housing. Neutral white Cree MCE (code - 000-ke5 - 4000 K) is installed on the metal core PCB sub base to help assembly. Evaluate led performance with and without secondary optics. The LED was selected to meet the energy star related color temperature (CCT) requirements and has sufficient flux, which far exceeds the minimum requirement of 200 lumens for lamps required by SSL household table lamps. The rated current of the LED is 370 to 430 lumens, the test current is 350 Ma and the temperature is 25 ° C. Considering the actual driving current (630ma) and steady-state operating temperature, the estimated lumen output range of the LED is 450 to 600 lumens, depending on the radiator design. The secondary optical element is fraen's off the shelf 32 degree reflector (frc-m1-mce-0r) designed for mc-e.

Figure 4: Custom radiator shell for lamp.

Figure 5: Cree MC-E is installed on the sub base and connected to the radiator.

Figure 5A: Cree MC-E includes mirror optics LED components are powered by ansenmey semiconductor ncp1014ledgtgevb LED driver evaluation board. This efficient driver can provide the required current isolation and adjust the driving current for the LED array. It has a universal input power range of 90 to 265 VAC, allowing one design to be used in multiple areas, requiring only the replacement of cables with wall plugs. This is not the case with the existing halogen core transformer, because it is specially designed for a line voltage range.

Figure 6: power factor performance of ncp1014ledgtgevb under normal load.

The evaluation board supports variable dimming using potentiometers with a current adjustment range of 100 to 630 ma. The 630 Ma maximum current is set to safely remain below the 700 Ma maximum operating current of Cree mc-e. Figure 6 shows a typical curve of power factor correction performance of ncp1014ledgtgevb LED driver as a function of input line voltage. As shown in the figure, for the U.S. line voltage range, the power factor is much higher than 0.8, far exceeding the requirement of Energy Star residential SSL lamp 0.7. The driver also meets the harmonic content requirements of iec61000-3-2 class C.

Figure 7 shows the LED drive board installed on the table lamp base. Note that since the original transformer providing balance is removed from the base, ballast weight is required to stabilize the lamp. In the portable table lamp design optimized for LEDs, the base will be wider and flatter to stabilize the lamp assembly without increasing weight. Figure 8 shows the LED driver demonstration board installed in the display cabinet without the counterweight required to support the head.

The data shown in Table 1 are collected on table lamps, original 50 Watt halogen bulbs and 35 watt alternative halogen bulbs. Additional measurements after switching to LED light sources show the presence or absence of additional optical reflectors to redirect stray light to a more central position. The illuminance expressed in Lux is a measurement of the luminous intensity on the surface at a distance of 0.5 meters from the light source

Figure 7: ncp1014ledgtgevb constant current drive plate is installed on the table lamp base.

Figure 8: with spare base.

Configuration setting source illuminance (Lux) pin (W) 50 W halogen lamp compared with Cree MC-E, fraen reflector optics high halogen 1462 56.6 LED (iDrive = 630 MA) 2596 10.9 low halogen 744 40.9 LED (iDrive = 100 mA) 646 1.67 35 W halogen lamp compared with Cree MC-E, no secondary optical high halogen 847 40.4 LED (iDrive = 630 MA) 962 10.9 low halogen 435 29.4 LED (iDrive = 100 mA) 236 1.67 Table 1: before and after comparison.

It is important to compare the illuminance directly below the light source, and the uniform distribution of light on the surface is also important. Therefore, select other test points at an offset of 0.25m from the center to characterize the distribution of light under normal operating conditions. The summary is shown in Table 2.

Bulb illuminance @ 0.25m offset (Lux) analysis left and right front mean sigma 50 W halogen lamp 853 800 727 793 51.6 LED optical fiber 580 577 529 562 23.4 35 W halogen lamp 496 485 443 475 22.8 led 518 527 490 512 15.7 Table 2: light distribution comparison

In this example, the converted led table lamp produces 13% higher illumination than the 35 watt halogen bulb, but the power consumption is reduced by 73%. Interestingly, after checking the performance of the magnetic transformer alone in the original 50 Watt table lamp, its loss is about 8.3 watts, which exceeds the 8.0 watts of the LED in the conversion table lamp. In other words, the transformer in the original halogen lamp base consumes more power than the LED in the converted table lamp. Figure 9 shows the comparison of brightness modes between the left halogen lamp and the converted LED lamp. correct. The comparison is between a 35 watt halogen bulb and an LED without any secondary optical elements. Note the uneven pattern generated by the tubular shape of gy6.35 halogen bulb. Instead, the LED assembly is mounted in a circular recessed area of the radiator, as shown in Figure 5. This provides a more rounded light pattern, illuminating evenly in all directions. High brightness LEDs are excellent in providing uniform directional light distribution due to their Lambert light structure.

Depressing the LED in the radiator facilitates the possibility of using secondary optics and avoids possible glare if the lamp is at the line of sight level. As shown in Table 1, the central illuminance is increased by 170% by adding an additional mirror optical system. Combining led performance with efficient drivers and off the shelf optics can provide lighting solutions far superior to halogen lamps.

Figure 9: light pattern of 35W halogen lamp and LED lamp. The surface of the exposed glass plate covering the halogen bulb is measured at 250 ℃. In contrast, the maximum temperature of the LED mounting substrate is only 77 ℃. Since this is a transformation, the existing airtight plastic shell for halogen bulb is reused. After removing the plastic cover, the LED installation temperature drops below 63 ° C; If the product is optimized for LED operation, the thermal environment will be further improved because the non ventilated cover can be redesigned or removed according to the final product design considerations. Also note that under normal driving conditions (350 MA), the LED installation temperature on the cover plate is 49 ° C.

The benefits of energy consumption are obvious. Higher efficiency, smaller size and weight and lower LED power consumption open the door to innovative lamp designs, which have always been limited by the limitations of halogen bulbs. When used in combination with appropriate LED driver circuits, effective solutions can be realized to simplify product design, so that the same products can be sold all over the world with a little change. In addition, the adjustable control allows users to further optimize the light output to meet their specific environmental needs, rather than one or two light levels of traditional halogen based table lamps. At lower brightness settings, the energy saving effect will be greatly improved.

The driver optimized for a common AC input of 90 to 265 VAC allows manufacturers to use a basic lamp design for all markets and only need to replace the power cord by region. Lamps based on the most advanced LEDs (such as Cree XLamp MC-E) and driven by high-efficiency constant current source drivers will allow the introduction of new durable and energy-saving general lighting products. Although this example shows the performance of the retrofit application, further optimization can be achieved if the lamp is specifically designed with LEDs from the beginning.

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