120 volt LED lights
What questions should I ask before buying an LED light?
I've seen claims that 120 volt LED lights can save me energy, but the claims sound too good to be true. Does a 3 watt LED bulb really give as much light as a regular 50 watt bulb? Is it worth spending $25 or $30 for one of these bulbs given the energy savings I'll get? What questions should I be asking when I shop for LED lights, so I can be sure I get something I'm happy with and that saves me money?
Answer from Green Energy Efficient Homes
In 2008 when I wrote my LED house lights page, I claimed that LED lights are not yet ready for prime time. 120 volt LED lights are definitely becoming more common now in 2011 than they were in 2008, but my opinion of them hasn't budged that much. The main problems I see with LED lights are light output, heat output, color temperature, dimmability, and unit cost. I'll cover each in more detail here, or you can skip straight to the section you're interested in:
- Light output of LED lights
- Heat output of LED lights
- Color temperature of LED lights
- Dimmable LED lights
- Cost of LED lights
Light output of LED lights
A single light emitting diode, such as those found in LED Christmas lights or an LED flashlight, sends a very narrow, weak beam of light. To make 120 volt LED lights that are useful as replacements for existing types of incandescent light bulbs, manufacturers typically design bulbs with a large number of light emitting diodes. For example, an LED light that replaces a standard 50-watt incandescent bulb might have 20 or 30 individual LEDs attached to the bulb assembly.
In general, the wattage output of 120 volt LED house lights should give you some idea of their brightness. But as I mentioned, an LED emits a narrow beam of light, so how well 120 volt LED lights do at replacing incandescent lights depends in part on how the diodes are configured on the bulb. If all the diodes point in the same direction, you will get a nice bright beam in one narrowly focused area, similar to a halogen spot light such as a GU10 or MR16. If the diodes are arranged in a dome configuration or even a near-sphere you will get a more diffuse distribution of light similar to a regular incandescent light bulb.
The problem with the light output of LED lights is how manufacturers measure it. Typically they measure light output, in lumens, at a particular spot, at a particular distance from the bulb, for example, four feet directly below the bulb. In the case of a standard incandescent or fluorescent bulb, the light output diminishes very progresively as you move laterally away from that spot directly under the bulb - because these bulbs distribute their light in a very diffuse fashion, which is why they are very well suited to lighting an entire room from a single fixture. But 120 volt LED lights, which generally send most of their light in one directly, might achieve the same lumens rating at that spot 4 feet directly below the light source, while providing almost no light to the surrounding area. This allows LED light manufacturers to make claims that their 2-watt LED light has the same light output, in lumens, as a 50-watt incandescent light, even though the LED light in question may be so dim you can hardly tell it is turned on.
I have seen this myself with a pair of 2 watt, 120 volt LED lights I bought to replace the halogen GU10's in my basement stairwell. The lights were very reasonably priced, at only $5 a piece, and made this exact claim. And yet the amount of light they provide is more akin to emergency exit lighting than the bright light of a halogen spot light.
So one question to ask when buying 120 volt LED lights is, for the stated light output, what was the beam angle the measurement was obtained over? You probably won't be able to find the answer to this on the product packaging or even the product website, so you'll have to either look at the light output at the store (assuming you can find a place that displays the lights turned on), or buy one bulb to try out, and then decide whether to return it or buy more based on its suitability.
Most 120 volt LED lights currently made have a hard time matching the beam angle of an incandescent or compact fluorescent (CFL) light bulb. 120 volt LED lights are made in bulb form with a cluster of LEDs and each LED is angled slightly off from the others to create a wider beam angle, but still few of them are as wide as you might need when replacing an existing bulb in an existing fixture.
You may want to use a 10:1 ratio rule of thumb for determining if an LED bulb of a given wattage has a chance of meeting the light output of the bulb it claims to replace. If the packaging on a 2 watt LED bulb suggests it can replace a 50 watt incandescent or halogen bulb, the claim is probably not going to stand up to scrutiny. But if it's a 5 watt bulb replacing a 50 watt incandescent, there is a reasonable chance the LED bulb may match the 50 watt incandescent in overall light output.
120 volt LED lights are more suitable for replacing halogen spot lights, since halogen lights have a more narrowly focused beam, similar to an LED. There are LED house lights s that can replace the more common halogen light bulbs such as MR16 and GU10, as well as many others.
There are also LED replacements for 4 foot fluorescent tubes. If you have such fixtures and use them heavily, these replacements are perhaps a worthwhile investment.
Heat output of LED lights
The other consideration for LED 120 volt lights, especially those replacing regular bulbs or pot light bulbs, is that they have to dissipate the heat they generate. LEDs generate far less heat than incandescents, but the heat is very damaging to them and shortens their operating life. So most 120 volt LED lights come with heat sinks (fins around the base of the light) to pull heat away from the heat-sensitive components. It's important to make sure the fixtures you are thinking of putting the LED bulbs into are not enclosed or otherwise likely to prevent heat from dissipating away from the bulb.
Color temperature of LED lights
One of the big complaints I hear with compact fluorescent lights is that their light is too 'unnatural', by which people really mean that the color is closer to blue than the yellow of an incandescent bulb. In fact, there is nothing unnatural about this light, it is just that it is closer to the color of natural daylight than the color of candle light. The term 'color temperature' is a numeric measurement of where on this blue-yellow spectrum a given light lies. Natural daylight has a bluish color temperature around 6,000 degrees Kelvin, while an incandescent light is typically yellower and sits in the 2,500 to 3,000 range. Most fluorescents are over 4,000 K. If you see 120 volt LED house lights that do not state their color temperature, or do not indicate that they are 'warm white' or have a color temperature below 4,000 K, you can probably count on them being unpleasantly bluish. This is certainly the case with the 2-watt 120 volt LED lights I bought for my basement stairwell: not only are they dim but they're a fairly gloomy shade of bluish white. Fortunately we don't spend that much time standing in the stairwell so this isn't a big concern.
One other thing to note on color temperature is that I have seen considerable variation between individual LED lights in the same lot, or even in the same package. For example, the LED under cabinet lights I installed last year in my kitchen had one puck that was distinctly bluer in color than the others. Fortunately I had bought two packs of three LED puck lights, and my cabinet installer told me I only needed two lights per valence, so I was able to find another bulb in the set that had the yellower tint to it. If you're buying 120 volt LED lights from a retail store youmay find it necessary to return some bulbs for exchange if you don't get a consistent color temperature from all bulbs.
So when shopping for 120 volt LED lights be sure to ask the question of what color temperature a particular bulb has, assuming you're like most people and don't care for the bluish tint of fluorescent lights. Look for a color temperature below 4,000K or a light labeled 'warm light'. And ask about the store's return policy if a light doesn't match the light output or color temperature it claims.
Dimmability of LED lights
To date I have not found any regular replacement LED bulbs that claim they can be used on a dimmer switch. In fact, in many cases the package explicitly states that the bulbs cannot be used on a dimmer switch. So if having dimmable bulbs is important to you, make sure you buy bulbs that explicitly state that they can be dimmed. (And let me know if you find any!)
There are two main reasons for wanting to dim lights. The first is to provide a varied level of lighting depending on the activities taking place in the room. For instance, you might want bright lights in your kitchen while you're cooking, but dimmer lights during a party or social gathering. For this application you might want to consider dimmer-free alternatives that let you get by with LED lights, at least in the busiest rooms in your house.
For example, our under-cabinet valence lights are LED pucks that use about 7 watts per pair - or 14 watts total - and provide enough lighting in the kitchen that we don't really need a dimmer switch for the kitchen halogen pot lights. We should really replace those pot lights with LED MR16's, as we could cut our power consumption from about 500 watts at full blast - or 250 watts at quarter-power mood lighting - down to about 70 watts at full blast, or 15 watts of cabinet lights for mood lighting. (The term 'we' here implies I need my wife's agreement - which is why so far we're sticking with the halogen lights!)
The other reason people might want to dim lights is to save energy. Note that dimming your lights doesn't save as much energy as you think. Dimming a light to 50% of its normal light output doesn't cut its energy use by half; it only cuts it by a quarter. A good rule of thumb is that for every 2% reduction in light output there is a 1% reduction in electricity use on a dimmer switch, so a bulb dimmed to 10% is still using 20% of the power of a bulb on full brightness. You'll still be better off with 120 volt LED lights at full blast, than halogen or incandescent lights dimmed to 10%, in terms of energy savings.
Cost of LED lights
A couple of years ago, replacement 120 volt LED lights for standard incandescent bulbs or halogen spot bulbs cost in the neighborhood of $30-50. I've seen a little movement on prices for bulbs already on the market, as well as some significantly cheaper bulbs becoming available, such as the ones I put in my basement stairwell, but these cheaper ones are cheaper mainly because they have very limited light output. In 2008 I suggested that LED lights are still a couple of years away from being ready for wide adoption, and it seems to me they are starting to sound like cheap nuclear power - always around the corner but never quite here.
Given the high up-front cost of LED replacement lights, you will want to be sure to buy them mainly for rooms where the lights tend to be on a lot, otherwise the savings in electricity won't pay for the bulb for decades. For example, my basement stairwell lights are probably only on for 10-20 minutes a day, and cost $10 in total. They are about 2 watts each and replaced two 50 watt bulbs, so I'm saving 98 watts whenever they're on. At 10 cents a kilowatt hour, they will save me roughly one cent for every hour they're on, which means I save one penny every 3 to 6 days. At best, they will pay for themselves in about five years at current electricity rates, which is not great for an energy efficiency payback period.
On the other hand, putting your first 120 volt LED lights in an area you don't use heavily can make sense if you want to evaluate them for light output and color before you upgrade the lights in a more heavily used area. That was my rationale for buying the stairwell lights.
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