Best quality LED A-lamp light bulbs provide a superior, energy-efficient alternative to incandescent bulbs, which have essentially been banned as of January 1, 2014. LED bulbs offer the same amount of light as an incandescent while using up to 80 % less energy. There still remains, however, a wide discrepancy in performance between LED bulbs and what consumers expect from them as alternatives to standard incandescent bulbs. This variation in performance and cost can be largely attributed to how specific LED bulb manufacturers solve the challenge of removing heat from the LED components within their bulbs.

This diagram of SWITCH’s 1st generation bulb illustrates how their liquid cooling technology works. The same thermal system is used in the SWITCH infinia™.

Although LEDs produce light efficiently, they operate at case temperatures that are often greater than100°C. This heat needs to be removed in order for the LEDs to run with greater efficiency (more light produced for the power applied) and more reliability (longer lifetime). First generation LED A-lamp bulbs were typically designed with the LED components attached to the top of a flat metal heat sink. Heat spread out radially from the LEDs through the heat sink to the cooler ambient air that comes in contact with the heat sink edges. These bulbs were more like flashlights, directing all light in one direction away from the heat sink. The top portion of these bulbs had a diffusing dome to help distribute the light, and the bottom portion of the bulbs had a heat sink attached to the Edison screw base. Heat removal was limited by the surface area of the heat sink. In a typical table lamp, these bulbs with diffusion globes directed 80% of their light toward the ceiling and only 20% toward the table. In comparison, a standard incandescent A lamp in the same application directs roughly 50% of its light toward the ceiling and 50% toward the table, providing uniform omnidirectional lighting.

The SWITCH infinia™ liquid cooled LED light bulb.

Newer LED bulb designs have improved on light distribution by placing LEDs in the center of the diffusion dome on a pedestal above the heat sink. This allows the light from the LEDs to radiate in an omnidirectional pattern closer to that of an incandescent bulb. This dramatically enhances light distribution but increases the heat conduction path length from the LEDs to the heat sink and to ambient air interface. This impedes heat flow from the LEDs. We have measured LED case temperatures of less than 110°C up to 135°C for bulbs which run at normal room temperature, and are being sold by large retailers. These high temperatures greatly reduce LED efficiency and reliability.

Advanced Benefits

SWITCH’s advanced LQD Cooling System™ bathes the LEDs inside the SWITCH infinia™ bulb in a liquid that efficiently distributes the heat produced by the LEDs across the bulb’s entire surface area to disperse heat through passive convection. As a result, these liquid-cooled bulbs provide greater flexibility and positioning of the LEDs for improved light distribution. SWITCH infinia LED bulbs are about 40 % more efficient in heat dissipation than air-cooled LED bulbs. Better thermal performance means these bulbs can be used in any fixture, even fully enclosed or recessed, and in any orientation without compromising light output or life.

The LQD Cooling System uses a liquid silicone coolant commonly used across many industries. It’s been proven to work in extreme temperatures and harsh operating environments. It’s an ingredient found in cosmetics, and is used for cooling large machinery and power plant equipment. Our liquid silicone is benign, electrically non-conductive, non-toxic, and non-staining. Liquid silicone is also optically transparent, doesn’t degrade the LEDs or bulb components in any way, and it doesn’t harm people or the environment.

Liquid silicone’s optical properties nearly match the optical properties of the LEDs in glass or plastic shells. This means that light moves more efficiently from the LEDs and through the bulb, than if the interior was simply filled with air. Air-filled bulbs reduce the light output by about 6%. This is wasted light and wasted energy!

SWITCH uses liquid silicone to passively cool the LEDs. This means that the bulbs don’t employ energy-consuming fans or pumps. The liquid in contact with the LEDs is heated, expanding and becoming more buoyant until it rises in contact with the cooler outer glass or plastic bulb shell. As the liquid cools, it becomes denser, dropping while contacting the outer shell, which all the while continues to cool the liquid. The cool liquid is then pulled up to the LEDs as the more buoyant hot liquid moves away from the hot LEDs. This process of heat removal is called “convection” cooling, and the convection process works in all orientations. It works so well that the LEDs only experience a couple of degrees difference between any orientation, which means that SWITCH infinia bulbs can perform perfectly for at least 25,000 hours in all orientations and fixtures, including fully enclosed. Most LED bulbs on the market are not suitable for use in fully enclosed fixtures.

Liquid cooled LED bulb in an industrial application.

In the SWITCH infinia design, the LEDs are placed on thin bendable metal finger-like surfaces, which causes the LED heat to come in contact with a greater volume of liquid. The LED heat removal is accomplished primarily through liquid convection where the LED heat is moved to the outer plastic shell. The precise positioning of the height and angle of the LEDs is to ensure that the light distributed from SWITCH clear and frosted bulbs exceed the uniform light distribution of an incandescent bulb, as well as Energy Star requirements.

The United Church of Chapel Hill (NC) replaced their 18-watt CFL bulbs with 89 SWITCH infinia 60 LEDs (10 watts) in autumn 2013 and are pleased with both the quality of the light they produce and the energy they save.

Another unique aspect to the SWITCH bulb design is the use of a volume compensation mechanism internal to the bulb. This mechanism allows the surface area containing the liquid to expand as the liquid is heated and contract when the liquid cools. This mechanism allows the liquid inside the bulb to always remain near room pressure through its heating and cooling cycle.

Applying the LQD technology to an air-cooled LED bulb can result in the LEDs running about 30°C cooler and light output to increase by 15%. The life limiting factors for an LED are the operating current and the LED temperature, so a cooler bulb with cooler LEDs can be more reliable. If the reliability of the bulb is sufficient, more power and a higher operating current can be applied to the LEDs, which will produce more light. LQD technology allows the bulbs to be optimized to bring a balance of bright light, excellent color quality, and highest efficiency.

Choosing the Right LED Bulb

The certification and labeling of LED bulbs is evolving. There still remains a high level of ambiguity, which can lead to consumer confusion in trying to replace a simple incandescent A-lamp bulb. Consumers usually buy an incandescent bulb based on light output and color. In other words, watts and warm or cool light.

The best way for consumers to choose the right LED bulb is by educating themselves about the different options available that meet their requirements for light output and color. They must also consider and compare suitability for the fixture – is it fully or partially enclosed? In addition, they should compare price, warranty, rated lifetimes and efficiency to ensure a smooth transition to LED lighting.

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Lighting Technology Magazine

This article first appeared in the May, 2014 issue of Lighting Technology Magazine.

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