White LED lighting is creeping into the mainstream. Holding back progress, however, are issues such as variations in color rendition and intensity, heat management, cost of manufacturing, market entry issues and consumer acceptance. For general-purpose applications for example task lighting, changing customer’s expectations from using several down lights or a fluorescent tube to using a single linear fixture employing a bulb with multiple LEDs is a tough sell.
While these issues need to be addressed by all LED lighting applications, the greatest hindrance to entering the consumer market is incentive. There is little incentive to replace an incandescent or fluorescent bulb unless the alternative has clear advantages. This is difficult to achieve, and has not been accomplished since the introduction of electric lighting.
However, many of these issues are resolved with the new white light LED solutions. Among the many advantages of LED lighting are: low power consumption; long life expectancy, which reduces replacement costs; robustness due to absence filament; environmentally friendly; can improve color quality; can be directional for task and display lighting; variety of colors are available; delivers a wide range of illumination intensity by increasing the number of LEDs; instant-on capability; dimmable; can be designed so that damage to one LED does not affect the others; adaptable to mobile and battery powered applications. Last but not least, the new generation of LEDs are expected to significantly outperform incandescent and fluorescent alternatives.
These are compelling features and have prompted the industry to introduce specialized solutions that target specific high-end markets, often requiring new fixtures. Unfortunately, the cost of replacing fixtures is price-prohibitive for most homeowners, leaving LED fixtures for new construction.
Architects are reluctant to design using LED fixtures due to UL requirements (see below), and the justification for the initial investment in these fixtures is further limited because the fixtures remain in the buyer’s home when the seller vacates.
Underwriters Laboratory
While Underwriters Laboratory (UL) states there is no approval process required as a prelude to entering the market, virtually every electrical supply and lighting concern, electrical contractor, and architect this author has contacted states that no local building inspector will approve a (LED) light fixture unless it has been UL-listed or UL-approved in some manner. This adds further delays and thousands of dollars to the process.
In addition, UL indicates there is no UL rating process for light bulbs of any kind. In fact this author had to convince the members of the UL lighting staff to consider the LED light bulb for evaluation based on heat concerns and efforts to deploy the bulb in fixtures. The members of the UL lighting staff agreed and acknowledge LED lighting as an up-and-coming technology; the staff admitted it is working on standards for UL listings. It suffices to say UL listing remains a gray area.
Light bulbs
In any event, an LED light bulb deals with some of the problems that current LED applications neglect. In addition to the advantages of LED lighting listed above, an LED light bulb can address the following.
* Does not require new light fixtures * Mobile, saving replacement costs when relocating * Can be used with standard diffusers and lampshades * Can be designed to have a compact size with intensities equivalent to comparably sized incandescent and fluorescent bulbs.
It would appear that this meets most of the requirements for an incandescent or fluorescent bulb replacement, but LED lighting is not without its own problems. Perhaps the biggest deterrent to the progress of LED lighting is the amount of heat generated when powered for maximum illumination. The hotter the LED, the faster the light output deteriorates and life expectancy diminishes.
There must be a balance between these issues. Since one of the main benefits of LED lighting is its potentially long life, it is essential to maintain and enhance this feature in the design of LED lighting solutions. Unfortunately, this limits most practical applications to 1-watt LEDs. Driving the current generation of 3- or 5-watt LEDs at maximum levels limits the life of the LEDs. This is disastrous for LED applications, which do not offer a means for replacing an exhausted LED. The purchaser can only wait until the last LED in the chain has burned out and then must dispose of the entire fixture.
Underdriving reduces heat load
One practical way to enhance LED life expectancy is to drive 1-watt LEDs at less than the standard 350 mA, or alternatively to drive 3 or 5-watt LEDs at 350 mA. This requires more LEDs to produce the same illumination, but it also provides a hidden advantage. More LEDs are distributed over a larger surface area, which can better disperse the reduced concentrations of heat generated by each LED.
This suggests that, no matter what a manufacturer claims, it is essential to mount the LEDs on the best possible heat dissipation material one can find i.e. metal. While efforts continue to produce a material similar to a circuit board that conducts heat, virtually all prefabricated LED mounting boards have an aluminum back plate to enhance heat dissipation. But this is not enough to guarantee a long life. LED applications that use a secondary heat sink mount will inherently outperform those without one.
Fortunately, much of the heat dissipation issues have been resolved for incandescent light fixtures. Incandescent bulbs have screw-in bases and fixtures that separate the bulb from the enclosure so the heat generated from the bulb can dissipate without creating a fire hazard. The challenge for LED light bulbs is to ensure that heat intensity and dissipation is comparable to that of a standard incandescent bulb. UL indicates that as long as the LED light bulb generates heat comparable to standard bulbs they are intended to replace, there should be no UL issues to consider. In other words, it is customary for a user to turn off a lamp and allow a bulb to cool before attempting to remove it from the fixture. Therefore, it would be acceptable to expect a user to do the same for any light bulb including new LED bulbs.
Standard incandescent replacements
Unlike other LED lighting solutions designed for specific applications, Berkeley Reclaimed Light focuses on a standard incandescent bulb replacement. Berkeley Reclaimed Light has developed a patent-pending device, which can be employed on almost any base. Each bulb consists of several high-intensity LEDs and a line-to-low-voltage DC driver, which can be internal or external to the bulb.
The LED bulb employs a unique heat dissipation system, the subject of the patent application, which is comparable to an incandescent bulb both in heat intensity and distribution. It attempts to distribute the heat evenly around the bulb in an effort to reduce excess heat, which can burn to the touch and limit the life of the LEDs. The Berkeley Reclaimed Light solution to the LED light bulb incorporates the following features as well as those already mentioned:
* Can be constructed for use with almost any light bulb base.
* Can provide directional light (for example using collimating optics mounted in a line along the bulb) as well as 360-degree illumination (by building the LEDs all around the lamp to mimic an Edison-like bulb).
* Can be constructed using recycled materials.
* Can be high intensity with heat management, or can be child-friendly producing little heat by employing fewer LEDs or by using a larger bulb surface area to dissipate more heat
* Can be repairable. Individual LEDs can be removed from the circuit board, replaced and re-soldered.
Approximately 25% of power generated annually is used for illumination. The LED light bulb can reduce this need significantly. The photo shows two lamps with LED bulbs. The lamp at left mimics clean halogen-like cool white and uses 12 high-intensity LEDs rated at 57 lumens, giving a total of 684 lumens. The lamp at right uses warm white high-intensity LEDs and mimics the standard incandescent bulb.
Fluorescent bulb replacements will follow; these will offer replace-once lighting to obtain warm white illumination not attainable from its fluorescent counterpart. Work environments can obtain the warmth of incandescent lighting without sacrificing energy efficiency.
