HID vs. LED: Brightness Costs Bucks

HIDs turn night into day and although not as bright, LEDs offer better contrast and almost limitless bulb life over incandescents. For the price, they ought to.

Anyone perusing the lighting aisle at the local Home Depot will have noticed that the lowly incandescent bulb is an endangered species, having been displaced by LEDs and CFLs. The burgeoning LED market has spilled over into aviation in the form of landing, taxi and recognition lights. (Thankfully, we’ve been spared the CFLs.)

Add to this the availability of another light technology, HIDs, and owners have more choice than ever in upgrading over the ancient GE tractor bulb that’s illuminated runways for decades. Never mind that this new technology costs 10 to 100 times more than an off-the-shelf GE 4509, how does it perform?

We’ll get to that in this article, but first note that the lighting market has expanded since we last examined the topic six years ago. There are more choices in HID and LED and more approved systems. In some cases, prices appear to have decreased, a welcome exception to everything else in aviation.

HID vs. LEDs

There’s nothing special about the common, incandescent aircraft landing light, other than it doesn’t last very long, is that it is likely to burn out on the darkest of nights, when you need it most. The gold-standard bulb, the GE 4509, has been around for years and is found on thousands of aircraft. There are even competitive providers of this lamp.

Here a word about nomenclature: Reflector-type bulbs are described with a PAR number—meaning parabolic aluminized reflector—describing the diameter in eighths of an inch. Landing and taxi lights are commonly either PAR 36 or PAR 46—4.5 inches and 5.75 inches in diameter, respectively. Upgraded lamps are generally available in both sizes, but PAR 36 is the most common.

HID—for high intensity discharge—predates practical LED technology by decades. The first HIDs appeared as street lamps more than a century ago and these evolved into the mercury and sodium-vapor lights that are common today. Those large systems were eventually miniaturized for vehicle use and these first appeared about 25 years ago. Aircraft applications were a natural fit and although LoPresti was the first to market HID with its Boom Beam, other competitors have joined the fray.

All work on the same principle, but vary in detail. The system consists of two components, a ballast and a lamp assembly, or burner. The ballast (actually a starter circuit) provides a high voltage to the xenon-filled lamp which strikes an arc inside the tube, vaporizing metal salts and creating a hot, bright plasma cloud. With a slightly lower voltage, the ballast sustains the plasma. This staged process is visible when the lamp first fires up; it takes a few seconds to reach full brightness.

David LoPresti told us that in the nearly 20 years the company has been selling HIDs, the lights have gotten smaller, lighter and brighter, with improved reflectors. Their initial product had a 35-watt ballast, but current offerings have an 85-watt unit. “The lumens per watt is higher than ever; our curve is almost straight up,” LoPresti says.

Better LEDs, Too

As HID has improved, so has LED; the diodes themselves have become more efficient and brighter. LEDs are more related to transistors than traditional bulbs or HID. They have p-n or positive-negative junctions that emit light when power is introduced across the junction. This has plusses and minuses for aircraft—or any—light applications.

On the plus side, LEDs are efficient. They produce more measurable light per power unit with less heat than do incandescents, although they run second to HID. But LEDs are small and while this is a plus, it introduces two more challenges. Individual LEDs have to be ganged and individually focused with their own reflectors and they can absorb only so much power without frying themselves.

The various manufacturers have addressed this with different design approaches. For example, the AeroLED, the brightest of the bunch we tested, has 16 LEDs while the Alphabeam and the Rigid have but four. While Teledyne uses a sort of Fresnel lens to focus the light output, our measurements showed that the two four-LED lamps had the lowest output and lowest perceived brightness. Whelen’s Parmetheus, with 12 LEDs, finished—where else?—behind those with 16 LEDs and ahead of those with four.

To gain a sense of how the lamps perform, we set up a test range with reflective markers at 100, 200 and 300 feet. The lamps were mounted in a rack positioned on a golf cart and aimed carefully by eye. To measure brightness, we used an Extech lux meter with its sensor mounted on a tripod for consistency. Although we don’t claim this to be a laboratory test, we think it gives a good idea of relative brightness. We took several readings for each lamp and averaged these.

There weren’t any real surprises in our trials, which generally followed the same results we had the last time we tested these systems for the March 2009 Aviation Consumer. As a baseline, we first tried the GE 4509, which proved brighter than all the LEDs except the AeroLED. But it wasn’t necessarily a better performer.

Why? Color temperature and beam spread, mainly. Although it measures brighter than most, the 4509 doesn’t look brighter than the best LED, the AeroLED Sunspot. Its beam is narrow and it doesn’t produce much contrast, so although you can see objects it illuminates, it can be harder to resolve the detail.

By contrast—literally and figuratively—the LEDs tend to have a wider, softer beams and a cooler color temperature. It’s more bluish. In our estimation, this made small details like cracks in the pavement or tiedown rings more visible. All of the lamps are sensitive to aiming so getting accurate brightness data is difficult. As the chart shows, the AeroLED was the brightest LED by a measurable margin, a distinction it easily held out to 300 feet. Also, its beam spread and color made it perceptively our top choice in this category of lights. It’s the one to beat.

And you can only beat it with raw brightness. If that’s your thing and you’ve got the money to pay for it, the HID blows everything away. The Boom Beam LoPresti sent us shot far into the gloom and illuminated the most distant target in sharp relief. Its color temperature is closer to daylight than the LEDs.

We used the default beam tuning, which is quite narrow, but in the well-appointed installation kit LoPresti provides are small tuning plates that allow the beam to be widened. We would recommend this; the Boom Beam has throw distance to spare and spreading some of those candelas out to the side of the aircraft would be helpful.

Speaking of installation, the LEDs are just drop-ins, but the Boom Beam will require four to six hours of shop time. That means installing one will probably total north of $2000 and for some models, way north. LoPresti provides an excellent kit and install manual, but there’s more to it than just replacing a lamp.

What to Buy

There’s no question that these lamps are a step up from the GE 4509. Just in longevity, the LEDs are supposed to be good for up to 50,000 hours and the HID for 2000. That means it’s both practical and recommended to leave them on all the time as recognition lights. Some LED models can also be configured as pulsing lights or, in pairs, as wig-wags. If you want to be seen, that’s one way of doing it.

For owners who fly frequently at night or go into dark airports where the runway and taxiway lighting isn’t the best, the Boom Beam or HIDs like it may be worth the money if the budget allows. The amount of light they throw really improves the ability to see and resolve runway details.

As for LEDs, at under $400, they’ve become a reasonably priced aircraft upgrade. Any of the lamps we tested will do, but our first choice, hands down, is the AeroLED Sunspot. Its bright, wide beam is just the right combination of illumination and width. We recommend buying the version with a protective lens, which retails for $364 from Aircraft Spruce.

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Paul Bertorelli is Aviation Consumer’s Editor at Large. In addition to his valued contributions to Aviation Consumer, his in-depth video productions on sister publication AVweb cover a wide variety of topics that greatly contribute to safety, operation and aircraft ownership. When Paul isn’t writing or filming, he’s out flying his J3 Cub.