First off, it’s all about the lumens. Lumens are the visible light given off by a source, and they are the ultimate goal. Wattage has often been confused with lumens, thanks to how incandescent bulbs are rated (everyone knows that a 60W bulb is not as bright as a 100W one), but more efficient lighting technologies have greatly changed the relationship between wattage (essentially power usage) and lumens (light output). For example, an incandescent might operate at about 12-15 lumens-per-watt (lm/W), while an LED bulb will be in the range of 40-50, a much greater luminous efficacy (Table 1-1). CFLs stack up well when it comes to lumens-per-watt, but they don’t have the lifespan of LEDs. CFLs have all sorts of other issues that we’ll address later, such as problems with disposal. And those LED bulbs? They are just today’s basic, commercially available LEDs—cutting edge models can be much more efficient. These models might produce over 150 lm/W, and even higher than that in laboratory settings.
Table 1-1. Wattage equivalency and lumens (from Energystar.gov)
|Wattage (W)||Lumens (lm)|
The incandescent bulb is a good place to start with any talk about lighting. This design has had tremendous longevity (over 130 years) and it makes for a cheap, versatile bulb. Unfortunately, this design is also power-hungry, inefficient, short-lived (with some exceptions), and fragile. They produce a minimum amount of lumens-per-watt, though they’ve made appreciable gains over the years, and are highly sensitive to power conditions. For example, a 5% reduction in voltage could double the life of a bulb while only decreasing light output by 20%.
One of the most notable strengths of the incandescent is the quality of the light it provides. This isn’t as easy to define as some of the other characteristics that will be covered, but it’s an important one when it comes to consumer adoption. After all, it’s nice to try to sell people on longevity and power savings, but if they think that the new bulbs are ugly or are too different from what they know, you’ll find them hoarding 75W and 100W incandescents before such bulbs are removed from the shelves.
Quality of light means that in order for people to be comfortable with the light these bulbs provide, the bulbs will need a color temperature that they find to be in an acceptable range, a high degree of color accuracy (usually measured by CRI), and a usable light pattern, to name a few qualities. The bigger point, as any early CFL or LED bulb buyer could tell you, is that if the bulbs don’t produce attractive light that people are comfortable being around, it won’t matter how long they last or how little power they consume.
Incandescents have good qualities, but ultimately their inefficiency means they are not a viable solution moving forward. Even modern incandescents can turn about 90% of the energy they take in into heat, which is obviously wasteful and inefficient in the extreme. Physicists might argue that this isn’t wasteful at all, and you might enjoy the heat they provide, but most of us want to leave the lighting to the lights and the heating to our furnaces. Before we demonize the long-standing bulb design, it’s worth noting that there is such a thing as efficient incandescence. While these are in fact more efficient versions of the incandescent bulb, they are still not at the level of top CFLs and LEDs. In fact, GE was working on a high-efficiency incandescent (HEI) for about 18 months, but gave up on it in order to focus its efforts on LED and organic LED (OLED) bulbs. HEIs were said to produce about 30 lm/W with the ultimate goal of doubling that amount.The halogen lamp is a type of incandescent that operates hotter and lasts longer, but its efficiency gains are minimal.
The much-maligned CFL solves some of the efficiency problems of incandescent bulbs, usually producing around 50 lm/W. Unfortunately, each bulb contains a small amount of mercury (about 4 milligrams per bulb), so disposal can be a problem, especially if the thin, usually helical, glass breaks. The bulbs have reasonably long lives, usually rated for 5,000 to 15,000 hours—but they don’t last nearly that long if they are used in short time spans as rapid cycling is bad for the bulbs. That means a CFL in a bathroom or closet might not last much longer than an incandescent bulb, despite what it says on the package. In fact, a CFL that runs for an average of 15 minutes at a time might last just 40% of its rated lifespan. Alternatively, a CFL that is used continuously from the first time it was turned on might last close to twice its expected lifespan.
CFLs saw a big jump in marketshare in 2007, capturing around 23% of the market, but have been in decline over the last year or so, despite the bulbs being widely available, affordable to purchase, and much cheaper to operate than incandescents. Part of this is due to an increasing number of consumers learning about the CFL’s use of mercury, but current economic conditions also indicate that people have simply been looking for a more affordable option. In that respect, incandescents still cannot be beat.
One of the most important characteristics of LED lighting is that they are solid-state. “Solid-state” might be a term we normally associate with computer parts (as in the solid-state drive) but it’s not something the casual LED buyer will ever consider. The concept is quite simple: rather than generating light through burning or gas-discharge, LEDs use semiconductors. The is the most fundamental and important distinction that determines why LED lights have their unique characteristics and will be able to have such an impact on the lighting market. As seen in other industries, semiconductors improve at an exponential rate and have a way of taking over wherever they are used. Lighting should prove to be no different.
Of course, LEDs are just one type of solid-state lighting; there are also organic LEDs (OLEDs) and polymer LEDs (PLEDs). Right now, the LED is the main focus of SSL adoption and its future looks quite promising, thanks to the efficiency gains it brings to the market. OLEDs and their carbon-based semiconductors have potential, but high costs mean they won’t be a viable option as soon as standard LEDs.
The advent of solid-state lighting doesn’t just mean more efficiency. Just as with the introduction of high technology to other parts of our lives—from our phones, to our mail, to our televisions—light is now high-tech. In this case, it’s not the tech that makes the difference, it’s that this latest step means our lights could soon be gadgets. Today’s technology brings with it intelligence and connectivity, which makes way for lights that can be tracked, controlled remotely, and designed to work with other devices. While the humble incandescent was just a conduit for electricity and output both light and heat, a modern-day bulb can be and do much more.
What does this all mean for the LED lamp? Basically, the time is ripe for growth. LED adoption is low at the moment, but not because purchasing one won’t pay off. An LED bulb will pay for itself many times over thanks to its energy savings, but the high initial cost is just too much of a hurdle for many businesses and is unpalatable for even more consumers. As prices drop we’ll see a dramatic growth, just as CFLs grew when it was clear that they could lead to long-term savings and could, in fact, provide acceptable light for our kitchens and living rooms, not just offices.