There are two kinds Type B LED tubes, single-end and double-end. A single-ended LED lamp is a lamp that has the live and neutral pins on the same side of the lamp. This end will be the “Input” end. If the single-ended LED lamp is being installed as a retrofit into a fluorescent fixture, you will need to replace the shunted lamp holders (also called tombstones) with non-shunted lamp holders on both sides of the fixture, which results more than doubled the installation time and labor cost. A double-ended LED lamp is a lamp that has the live and neutral pins on the opposite side of each lamp. Fluorescent lamps (LFL) are typically double-ended as well, making retrofit applications easier to complete with double-ended LED lamps. Double-ended lamps can be used with shunted or non-shunted lamp holders. When upgrading to LED lamps, customers have the option to utilize their existing lamp holders, which helps to reduce the average retrofit installation time.
Safety Issue
When a single-ended Type B LED tube failed in a retrofitted fixture, unsuspecting custodial staff may insert a fluorescent tube into the retrofitted fixture, thus causing it to short out immediately. This was due to the fact the bi-pins of the fluorescent tube are connected. There were incidents where the fluorescent tube literally exploded at 277V under such a scenario. The warning label affixed on the fixture (advisory against using a fluorescent tube on retrofitted fixture) was of little effect if a custodian or maintenance person didn’t bother to read it. It is due to this liability (and to avoid legal issues arising from such situations) that none of the top three US lighting manufacturers ever made or sold single-end Type B LED tubes.
Considering easy installation, most manufacturers, the distributors, the contractors, and the end-users prefer using double-end LED tubes. But the trend didn’t last for a while because UL was quick to identify the electric shock hazard with such a product, and subsequently mandated an anti-shock protection requirement in the UL 1993 safety standard. Most Type B double-end LED tubes disappeared from the market. Some manufacturers got their Type B double-end LED tube certified through another safety body, ETL, by exploiting a loophole of the ETL standard on not requiring the anti-shock protection. It is worth noting that these ETL certified tubes can’t meet UL anti-shock requirements for there is no anti-shock protection.
Shock hazard Issue and Safety Standard
Normal fluorescent tube lamps are safe due to the fact that the gas inside the tube first has to be ignited before there is a conductive path between the pins on the two end of the tube. This safety is necessary when the tube is being installed into a fixture while the voltage is not disconnected from the mains. In the situation when the lamp is not inserted correctly (one end of the tube inserted and the other not yet) the pins at the not-inserted-end are insulated by the gas in the tube.
For LED tubes there is a conductive path between the two ends (connected by an electronics circuit) of the tube and safety is not guaranteed. When inserting one end of the tube into a fixture with power on, touching the other end of the tube will cause an electric shock.
To address shock hazard issue the safety standard UL1993 defines the LED tube re-lamping test setup and the passed criteria. Fig1 shows the test setup. One end of the tube shall be connected to its intended source of supply while the other end of the tube is considered accessible and therefore is connected to the shock hazard measurement meter circuit. The shock hazard measurement meter circuit simulates the human body and the current is weighted according to the frequency. The meter measured leakage current shall not exceed 5.0MIU RMS (7.07MIU peak) as UL1993 defined. Please notes that the MIU peak value of 7.07 is 1.414 times the RMS value of 5.0 because it assumes the leakage current is a sinusoidal waveform. When the leakage current is the non-sinusoidal current, take precautions to ensure the peak value rather than the RMS value is read.
The SIMPSON 228 Leakage Tester has a built-in shock hazard measurement meter circuit, therefore in most cases, people are willing to choose the 228 Tester directly to complete the Re-lamping test of the LED lamps. It should be noted that SIMPSON 228 Tester is allowed only when the leakage current is a sinusoidal waveform as claimed in its operation manual. If the leakage current waveform is a non-sinusoidal wave, such as a pulse waveform, it should use a leakage current tester such as TOS3200 from KIKUSUI rather than SIMPSON 228.
Type B tube with anti-shock Protection
Since UL1993 re-lamping test was released, the double-End Type B LED tubes built-in with anti-shock protection have been soon introduced into the market. The anti-shock protection is realized by an installation detection circuit in the front of BUCK converter. As known there are two kinds of installation detection circuits in the market, pulse current detection and grid impedance detection, as shown in the Figure below.
In the pulse current detection circuit, a detection pulse is generated by a pulse generator to close the switcher for a while, detection circuit detects the installation state of the lamp by sampling lamp current Ipk through the resistor Rs during the while, and then to determine switcher whether to cut off lamp driving signal based on the detected result. In certain embodiments, the Ipk is heavily dependent on Vin and Vo at the pulse sampling moment. It is not a stable parameter. This is why some double-End Type B LED tubes with pulse current detection can’t light on under normal conditions but recover soon in the next turn-on.
The grid impedance detection circuit realizes anti-shock protection by detecting a change of impedance Zs on the grid. If electric shock occurs, which means a human body is connected in the power loop, the grid impedance thereof, normally around 10Ω, shall increase tremendously. Therefore once the circuit calculated grid impedance Z is above the pre-set impedance value range, the switcher will cut-off the power loop of the lamp for safety operation. Because the grid impedance Zs is independent of line voltage Vin and output Vo, it’s a much more stable parameter than Ipk. Therefore double-End Type B LED tubes with grid impedance detection perform much better than Type B LED tubes with pulse current detection.
The leakage current of double-End Type B LED tubes with pulse current detection is a non-sinusoidal pulse wave, while the leakage current of double-End Type B LED tubes with grid impedance detection is a sinusoidal wave. Considering both Type B LED tubes are existing in the market and it is hard to identify who is who, we strongly recommend evaluating the safety of double-End Type B LED tubes by using the KIKUSUI TOS3200 but not the SIMPSON 228 tester.
These anti-shock protection circuits are achieved by ASIC(Application Specific Integrated Circuit) such as LT2600, SP328, or JW1818, which are designed to detect the leakage current during lamp installation, for double-end Type B tube safety operation. Therefore double-end Type B tube can now be used without relamping safety issues. The product is taking off in popularity.
Risks of Mis-lamping
As with any new technology, there are always drawbacks and the double-end Type B LED tubes with anti-shock protection are no different. One of the major problems of such product is mis-lamping. In reality there are many mis-lamping cases where the lamp is mistreated as Type A tube and connected to a fluorescent ballast, including instant start ballast, programmed start ballast, dimming ballast, or even emergency gear, etc. A well-designed Type B tube should not light on under any mis-lamping situation, it can remind the installer that a mistake is existing and bypass ballast immediately. Unfortunately, there are some double-end Type B LED tubes still light on under mis-lamping situation and neglected by installers, which may results a big fire accident because ballast keeps burning these Type B LED tubes under mis-condition in coming weeks. Several fire accidents have been reported are all related to such kind of product by this cause (Fifth fire at Columbus City Schools could cost up to $300,000 to clean up).
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