Categories Lamp

What Goes into the Design of LED Retrofit Lamps?

In a LED retrofit lamp, it is the light engine comprised of LEDs (discrete or chip on board) that emits the light that you see. The LEDs in the lamp operate at a temperature much higher than ambient, resulting in lower lumens, and this thermal efficiency factor lowers the lamp efficacy (lumens per Watt or LPW) below that of the intrinsic LEDs. Depending on the application, some LED lamps also have a form of secondary optics to shape the pattern of the light. Not all the light emitted by the LEDs makes its way out of the lamp. There is a light extraction efficiency associated with the whole optical system and this also lowers the efficacy of the lamp below that of the intrinsic LEDs. Finally, there is a driver efficiency factor (not all of the input power to the lamp ends up being delivered to the LEDs) which again reduces the lamp efficacy. It is the product of these three individual efficiencies which gives the overall factor to help the designer determine the final lamp efficacy.

Lamp designers from reputable manufacturers focus on lamp performance while accounting for each of the efficiencies mentioned above and also keeping in mind the need for the product to be affordable. Fly-by-night vendors often do not understand or care about these efficiencies.

In general, higher thermal efficiency is associated with a lower LED solder point temperature. This is possible with good thermal management by a suitable combination of proper materials for the heat sink, adequate surface area, proper choice of interface materials and good contact protocols. High optical efficiency, especially for omni-directional lamps, may need suitable lens design and proper choice of optical materials.

Driver electronics is complicated. A high efficiency driver allows one to reduce the total input power to the lamp for a given lumen output from a specified light engine. This is because in a high efficiency driver fewer watts are lost in the driver circuitry with a larger fraction of the input power being delivered to the LEDs. Power dissipation in the driver results in heat so a higher efficiency driver helps lower the temperature of the driver components allowing the use of lower cost capacitors and inductors for example.

Various design attributes influence the driver efficiency. One of them is whether the driver is isolated or non-isolated. While the latter tends to have lower losses and higher efficiency, one has to be careful to ensure that electrical safety requirements are met to avoid any shock etc. Unlike fly-by-night vendors, reputable manufacturers of LED lamps pay proper attention to this. A non-isolated driver design generally calls for fewer components, allowing a smaller driver footprint, and so is preferred for smaller form factor lamps.

Dimming performance is directly related to the driver design. Dimming drivers, for example, incorporate a bleeder circuit with resistive and capacitive components that provides the latching and holding current and prevents the TRIAC from misfiring. Bleeders can be passive or active. An active bleeder, where the resistor is only on when needed, may be the preferred route when high driver efficiency is needed. This may happen when one has to design a higher wattage LEDr lamp while keeping the cost of the heat sink under control. In this case, driver component temperatures are very critical. A passive bleeder may suffice for low wattage LEDr lamps where the driver efficiency may not be that critical. Even the type of fuse that is used for the driver can influence the dimming performance and also affect the driver efficiency.

In summary, several complex technical variables influence the optical, thermal and driver efficiencies in a LED lamp. Reputable manufacturers differ from the crowd of lesser vendors in that the former pay attention to all of these efficiencies when they design lamps for the customer while keeping cost in mind.

Categories Lighting

UL Lighting Standards Update

UL Standards encompass UL’s extensive safety research, scientific expertise and uncompromising focus on quality. With over a century of experience and the development of more than 1,000 Standards, UL continues to break new ground in its mission to help create a safer, more sustainable world. The below standards update for the lighting industry was originally published in UL’s Lumen Insights Newsletter, Year-end edition.

UL 1598 – Luminaires (Tri-national standard)

  • Next revision cycle started, which will be a 2-year cycle. Call for Proposals due date was June 22, 2013. The UL proposals were prepared and sent on September 22, 2013 to CSA (the Publication Coordinator) for Technical Harmonization Committee review.

UL 1598C – Light-Emitting Diode (LED) Retrofit Luminaire Conversion Kits

  • Proposed 1st edition went out for ballot on March 15, 2013. The proposal achieved consensus and a STP meeting was held on July 17, 2013 to discuss the comments received. Responses have been posted and revisions were proposed in a recirculation Work Area in CSDS on November 8, 2013 with a due date of December 9, 2013.

UL 1993 – Self- ballasted Lamps and Lamp Adapters (Tri-national standard)

  • Next revision cycle started. Call for Proposals were due on September 22, 2013. The proposals are being prepared for Technical Harmonization Committee review.

UL 8750 – Light Emitting Diode (LED) Equipment For Use In Lighting Products

  • Proposal went out for ballot on September 21, 2012 and also discussed at November 2012 STP meeting. The proposal related to adding requirements for dimmable LED drivers for use with solid-state dimming controls electrically wired in series with the mains supply. The proposal went out for recirculation on May 31, 2013. The revisions were published on September 19, 2013.
  • Multiple proposals went out for preliminary review on October 24, 2012. These proposals were discussed at the November 2012 STP meeting. Some of the proposals were reworked and went out for ballot on June 7, 2013. The remaining topics will proceed separately.Error! Hyperlink reference not valid. Responses have been posted and revisions were proposed in a CSDS recirculation Work Area on October 11, 2013 with a due date of November 11, 2013.
  • Multiple proposals went out for preliminary review on October 14, 2013 with a due date of November 8, 2013. These proposals will also be discussed at the November 2013 STP meeting. Link to the summary of topics: http://ulstandardsinfonet.ul.com/sot/b8750_1_20131014_sum.html
  • STP meeting is scheduled for November 19-20, 2013 at the Embassy Suites Hotel in Deerfield, IL.

UL 8752 / ULC-S8752 – Organic Light Emitting Diode (LED) Panels

  • Multiple proposals went out for preliminary review on May 28, 2013 and for ballot on July 12, 2013. The revisions were published on September 30, 2013. This is a joint UL/ULC Standard.

UL 8753 / ULC-S8753 – Standard for Field-Replaceable Light Emitting Diode (LED) Light Engines

  • The 1st edition of the joint UL/ULC Standard for Field-Replaceable Light Emitting Diode (LED) Light Engines, UL 8753 / ULC-S8753, was published on July 31, 2013. There is no current UL standards activity.

UL 8754 / ULC-S8754 – Holders, Bases, and Connectors for Solid-State (LED) Light Engines and Arrays

  • The 1st edition of the joint UL/ULC Standard for Holders, Bases, and Connectors for Solid-State (LED) Light Engines and Arrays, UL 8754 /ULC-S8754, was published on July 31, 2013. There is no current UL Standards activity.

UL 935, UL 1029, UL 542 – Ballasts (Tri-national Standard)

  • The draft of Part 1 of the proposed Standard, covering general construction and test requirements is being reviewed by the CANENA Harmonization Committee (THC34/SC34C) and being prepared for preliminary review.
  • The Part 2 documents which will include specific requirement for the various product types still need to be developed.

UL 935 (current UL Standard, 10th edition)

  • Proposal went out for preliminary review on May 29, 2013 related to the addition of requirements for ballasts intended to be dimmed using solid-state dimming controls electrically wired in series with the mains supply. Another proposal went out for preliminary review on July 26, 2013 related to revising the arcing test method in Section 30. These proposals went out for ballot on October 18, 2013 with a due date of December 2, 2013.

UL 153 – Portable Electric Luminaires

  • Proposal went out for preliminary review on October 4, 2013. The proposal was related to a revision for Paragraph 24.1, exception No. 3 and to add the definition of “LVLE” circuit. The proposal will be issued for ballot on November 15, 2013 with a due date of December 16, 2013.

UL 1786 – Direct Plug-In Nightlights (Bi-national Standard)

  • Next revision cycle started. Multiple proposals went out for preliminary review on October 17, 2013 with a due date of November 7, 2013. Link to the summary of topics: http://ulstandardsinfonet.ul.com/sot/b1786_3_20131017_sum.html

UL 496 – Lampholders (Bi-national standard)

  • Multiple proposals went out for ballot on February 24, 2012 and recirculation on March 15, 2013. Link to the summary of topics: http://ulstandardsinfonet.ul.com/sot/b0496_13_20120224_sum.html. The proposals are being prepared for publication in the Standard. The revisions were published on November 25, 2013.

UL 1088 – Temporary Lighting Strings

  • Proposal went out for preliminary review on September 19, 2013. The proposal was to allow for the use of energy efficient light sources in temporary lighting strings. The proposal will be issued for ballot on November 1, 2013 with a due date of December 16, 2013.

UL 2108 – Low Voltage Lighting Systems

  • Multiple proposals went out for preliminary review on August 27, 2013. The proposals went out for ballot on October 4, 2013 with a due date of November 18, 2013. Link to the summary of topics: http://ulstandardsinfonet.ul.com/sot/b2108_1_20131004_sum.html

UL 1573 – Stage and Studio Luminaires and Connector Strips

  • Proposal went out for preliminary review on September 13, 2013. The proposal went out for ballot on October 18, 2013 with a due date of November 18, 2013. The proposal was to add requirements of 2014 NFPA 70 Section 520.68 (A)(3) to UL 1573.

UL 1838 – Low Voltage Landscape Lighting Systems

  • Multiple proposals went out for preliminary review on September 20, 2013. Link to the summary of topics: http://ulstandardsinfonet.ul.com/sot/b1838_3_20130920_sum.html. The proposals will go out for ballot on November 8, 2013 with a due date of December 23, 2013.

UL 924 – Emergency Lighting and Power Equipment

  • Multiple proposals went out for preliminary review on April 24, 2013. The proposals went out for ballot on August 16, 2013 with a due date extended to October 30, 2013. Link to the summary of topics: http://ulstandardsinfonet.ul.com/sot/b0924_9_20130816_sum.html
  • Proposal went out for preliminary review on September 11, 2013. The proposal went out for ballot on October 18, 2013 with a due date of November 18, 2013. The proposal is to delete SH3.2 (using photometric data to show conformance)

UL 676 – Underwater Luminaires and Submersible Junction Boxes

  • Proposal went out for ballot on July 12, 2013 and recirculation on September 30, 2013. The proposal was related to non-metallic and isolated, low voltage luminaires. The proposal is being prepared for publication.

UL 48 – Electric Signs

  • Proposal went out for preliminary review on December 24, 2012. The proposal was related to two topics: (1) Clarification of drain opening requirements and (2) Grounding and Bonding Marking. The next step is for the proposal to go out for ballot.

UL 48B – Changing Message Signs and Displays

  • UL is currently developing proposed 1st edition for UL48B.

UL 879 – Electric Sign Components

  • Call for Proposals went out on October 14, 2013 with new proposals due November 22, 2013.
Categories LED

LEDs and Movie Stars

One of the many virtues of LEDs is that they have an exceedingly long life span. Perusing a few data sheets will show an oft-cited figure of 50,000 hours. Indeed, if installed in a domestic setting like a kitchen or lounge where the lights are mostly on after dark and used on average, say, 6 hours per night, this means the LEDs should last for 23 years. But what does “last” actually mean? At the end of life, tungsten bulbs simply cease to operate when the filament ruptures, so it is quite obvious when one has blown. Fluorescent bulbs tend to flicker and flash when the tube is no longer able to sustain conduction and replacement is then necessary due to the nuisance factor. LEDs on the other hand simply fade away.  They just get progressively dimmer, as though running on batteries that are very slowly running out.

There are various definitions of how dim an LED can become before it is considered to have reached end of life. For general lighting applications research has shown that most people will be oblivious to a reduction in illumination of up to 30 percent, particularly if it occurs gradually. For this reason the useful life of a high brightness LED is often defined as the point at which light output has declined to 70 percent of initial lumens. For an indicator LED on an instrument panel a 50 percent reduction might be acceptable, while in a scientific instrument it could be 5 percent or less.

 

By far the largest factor causing LEDs to dim is its time at temperature. High temperatures in LEDs cause a variety of undesirable processes to occur that are irreversible and reduce the ability of the device to produce light. This means that to achieve long life special attention must be paid to the materials used to conduct heat away from LEDs. A good slab of aluminium with a thin coating of Nanoceramic as the thermally conductive dielectric is a good choice, and the difference of just a few degrees can have an enormous, exponential knock-on impact on the lifetime of the LED.

A recent study by the Lighting Industry Association Laboratories showed that high brightness LEDs mounted on Nanotherm Nanoceramic PCBs operated 5 percent cooler than the nearest commercial competitor substrate. But don’t be tempted to think that just because 5 percent of 100°C is only 5°C that such a reduction is not worth bothering about, the underlying physics begs to differ. It turns out that the reduction in lumens of an LED is an above unity exponential function of the LED temperature. So a small difference in temperature makes a huge difference in the time it takes an LED to reach a particular level of dimness.

LEDs are quite like movie stars. They start as bright starlets and the hot ones burn out early, while those that stay cool have long careers and fade slowly from the limelight. As limelights in theaters have been replaced by LEDs, modern movie stars can now stay in the LED spotlights and wait for them to fade over 50 years instead!