Post Date: 08/13/21
Converting to LED can be a complicated process. In Part 1 of our Converting to LED guide we covered some of the benefits, costs, and savings associated with switching from Halogen to LED replacement lamps. In that article, we showed how LEDs pay for themselves quickly through reduced energy and maintenance costs. We also discussed how local, state and federal incentives can help offset the startup costs of making the switch. In addition to these financial incentives, LEDs have some inherent properties that make them attractive, like the fact that unlike Halogen, they do not propagate radiation in the UV spectrum — a significant added benefit when lighting sensitive materials.
While converting to LED replacement lamps includes some notable gains, there are also a few potential hidden issues of which you should be aware. This is especially true in cases where LED is being integrated into an existing infrastructure. This article will cover what to consider before converting to LED replacement lamps and will go into detail about the differences between LED replacements and other options.
What to Consider Before Converting to LED Replacement
The benefits of LED don’t come without a few caveats. Before replacing existing lighting with LED replacement lamps, there are a few things to consider.
Unlike incandescent sources, like Halogen lamps, which thrive on high thermal loads (in Halogen lamps, high temperatures are actually required for proper functioning and lamp longevity), LED sources are incredibly heat sensitive. In fact, a fairly large portion of LED replacement lamp and integrated LED luminaire design is specifically dedicated to heat management. Many people familiar with LED lamps and fixtures are probably also familiar with the telltale heat-sink that helps move thermal loads away from the LED to ensure color stability and lamp life over time.
While LED replacement lamps are mechanically and electrically designed to replace legacy Halogen sources, the fixtures into which they are being installed do not typically include heat sinks or have internal airflow to help alleviate thermal stress. As a result, when installing LED replacement lamps into legacy Halogen infrastructures, it is important to ensure that the lamps are rated for a fully enclosed fixture.
If lamps are not rated for fully enclosed fixtures, then they can be subject to thermal shock. Many LED replacement lamps have internal shut-off mechanisms to protect the lamp from such shock, which can result in flickering (as lamps try to stabilize thermally below their limits), dimming, or in the lamp shutting off until it reaches a suitable temperature to resume operation. Even when lamps do not exhibit any of these behaviors, lamp life and color stability over time can be greatly reduced.
Typically, lamps rated for use in fully enclosed fixtures manage heat by reducing power input and lumen output. While this may protect the lamp, it can also significantly impact lighting design. In some instances, LED replacement lamps rated for fully enclosed fixtures provide only half of the output of the Halogen lamps that they are replacing.
In some instances, it may be necessary to purchase new fixtures designed around the thermal requirements of LED replacement lamps. Some manufacturers also provide retrofit kits for certain recessed applications. You should take this into consideration when planning budgets for LED conversion, and run tests to ensure that lighting levels meet program requirements.
As indicated in the previous section, when adopting LED replacement lamps, it is important to check the delivered lumen output data for the lamp. Many LED replacement lamp manufacturers will provide rough equivalency to standard Halogen sources. Sometimes, these equivalencies are misleading, or it may not be feasible to use the equivalent lamp due to thermal management issues. The only way to compensate for the lower lumen output of replacement LED sources is to add more lamps, which may require purchasing additional fixtures.
This is especially true for larger format lamps, like PAR38, where it was possible to use very high output Halogen sources. When converting spaces that use these kinds of high output lamps, standard best practice is to test potential LED replacement lamp alternatives to ensure that output meets program requirements. If this is not possible, it may be necessary to use an Integrated LED luminaire capable of providing equivalent output.
Some halogen lamps, like an MR16 GU 5.3 base lamp, require a power supply (for a Halogen lamp, this is called a “transformer”). This converts line voltage to the required input voltage of the lamp. Most legacy power supplies are rated for comparatively high wattage (like 75 watts for the MR16 lamp described above).However, LED lamps require very low wattages. For example, a 7-9 watt LED replacement lamp may replace a 50 watt Halogen lamp.
The comparatively low wattage requirements of LED replacement lamps can cause issues. Since the original power supply for the fixture is designed around the larger load requirements of Halogen lamps, when the load is much lower, the transformer may have difficulties registering it. This typically occurs during dimming, and can result in flickering or an abrupt transition to off.
For line voltage luminaires, like PAR30 and PAR38 fixtures, this should not pose an issue, although the standard best practice is to check with the lamp manufacturer to assess dimming compatibility when dimming is involved.
In addition to potential issues with electrical compatibility, especially during dimming, some LED replacement lamps may also exhibit anomalous behavior due to feedback, especially where there are large quantities of fixtures on a circuit. All LED lamps introduce low level noise into the line, and all LED replacement lamps have some form of filter that cancels this noise out. However, the noise threshold for lamps varies by manufacturer. When large numbers of lamps are powered through a circuit, the noise fed into the line is amplified, and depending on the loading, may exceed the noise threshold of the lamps. When this happens, the lamps will start strobing synchronously.
This issue is easy to diagnose because it will always occur at a threshold condition. For example, an installation may perform fine until a certain number of lamps is reached (for example, the 20th lamp is installed). Removing the lamp will cause the strobing to stop, adding it back in will cause it to start. If you encounter this issue, there are two options:
- Stay within the threshold
- Test alternative lamps that might have better noise filtering mechanisms
Lamp Geometry and Specialty Fixtures
Many cultural institutions use specialty fixtures, like wall-washers, to illuminate their collections. These fixtures have highly specialized optical assemblies. They typically include a kick-reflector (that reflects light up to the top of the wall), and a universal spread lens (to push light out laterally along the wall). The performance of these types of luminaires is highly dependent on the relationship between the light source and the optical assembly. In this regard, the industry greatly benefited from standardization in the Halogen market, which ensured that every lamp (regardless of manufacturer) fell within certain physical parameters.
While much progress has been made in this regard, LEDs are still not as physically standardized as Halogen lamps. This disparity is compounded by a number of other variables that may affect the performance of specialty fixtures, like wall-washers. The first is the thermal issue discussed earlier in this article — since LED replacement lamps are thermally more sensitive, using optics (like a universal spread lens) which blocks front ventilation can result in overheating, flickering, shortened lifespan, shut-off or failure. The second is that LEDs propagate light much more directionally than Halogen sources do, which can be an issue when attempting to modulate distribution in specific ways.
All of this means that replacement LEDs may not achieve comparable light distribution or performance. The results can be scalloping, haloing, uneven light distribution, or other undesirable effects. It may be necessary to test a variety of LED replacement lamps when using them in a specialty fixture to achieve the desired distribution.
The Importance of Testing
The most important part of converting to LED replacement lamps is to test everything. Testing is effective at two scales. At the smaller scale, it is advisable to try a variety of lamps in one or two fixtures. This will make it possible to narrow the scope and focus on lamps that produce enough of the right kind of light, at the appropriate distribution(s) based on the application. Once the scope has been narrowed to 1-2 potential candidates, mock up a section of the space in which conversion will occur. This should be representative of the desired range of performance required. Replace around 30 lamps to see how it affects the space, and to ensure that the lamps are not sensitive to feedback, flicker or other anomalous behavior when installed at scale. This is a good way to see the difference between LED and halogen lamps, while testing for the issues noted above.
In a series of lectures and articles published after the conversion of the Smithsonian’s Renwick Gallery, lighting designer Scott Rosenfeld emphasized the need to test, test, and test some more. Not only was the Renwick one of the earliest adopters of LED replacement lamp technology, but it also set the gold standard for LED conversion in museum environments.
More Sustainable...to a Point
One of the selling points of LEDs is that they are more sustainable. While this is true in terms of their operating lifespan and energy consumption, it does not hold true in the “cradle-to-cradle” sense of the complete product lifecycle. Unlike Halogen lamps, LEDs are considered “hazardous waste,” and as such require special disposal and/or recycling, which may incur additional cost to users. This designation reflects the levels of copper, nickel, gold, silver, lead and arsenic used in typical LED sources. The designation includes both materials that have toxic properties in and of themselves, and those that are scarce and may require more aggressive means of extraction. In addition to these materials, replacement LEDs also frequently contain plastic or silicone, non-biodegradable TIR optics.
While LED replacement lamps last longer, the industry may be facing challenges related to disposal as early LEDs already begin to reach the end of their lifecycle.