Artificial light has made much of human development possible. Since the discovery of fire, light plays a central role in our lives, extending our hours of life, creating mood and atmosphere in our homes, and increasing our productivity.

Since the rising concerns in the last century about the electricity use of traditional incandescent light bulbs, the mainstay of our post-industrial lighting solutions, there have been many alternatives brought to market. Some of these are excellent replacements for the standard lightbulb in most cases but others are not such great alternatives.

This guide sheds light on these issues, an helps pick the right lamp for the right purpose. Also, since energy use is a concern, it's important to realize that new technologies do not always outperform older technologies in this department. Sometimes smart new ways of using old techniques have remarkable results. This guide is written to show the basic concerns when choosing lighting fixtures and technologies for indoor use, but they may also be helpful in other applications.

This guide starts with some general observations about light, which introduces some important definitions and terms used elsewhere in the guide. This is followed by a discussion of the seven main properties of artificial light sources, which are Spectrum, Intensity and Energy Use, Spread, Consistency, Format, fitting & Type, Longevity and Reliability, Materials and Cost. It concludes with a range of examples of some of our own experiments and experiences.

To understand some aspects of artificial lights, it's good to investigate some properties of light in general. There are basically only two properties of light in general that concern us: intensity and spectrum. Together these define the light we care about. Intensity is rather self-explanatory: the amount of light emitted. Light is defined as that part of the electromagnetic spectrum that can be seen by an average human, and is a subset of this energy.

Intensity of light can be measured in Lumens, and Lux, where Lux is Lumen spread over a certain area. Lamps are usually expressed in Lumens. More on that later.

Spectrum

The spectrum of light defines the set of wavelengths present in the light in question. Sunlight contains the 'full spectrum', but also includes infrared, ultraviolet and other radiation beyond those wavelengths. Even though sunlight contains the full spectrum of visible light, it does not contain an equal amount of all wavelengths. The below diagram shows an approximation of the spectrum and intensity of direct sunlight.

Diagram of the solar spectrum. Note that a large amount of energy (area underneath the curve) is present in infrared.

The curve in this diagram is called a 'spectrum-curve'. This corresponds to the perception of sunlight as 'warm' light, since it has higher intensities in the red spectrum than in the others. The diagram shows light received by earth at atmospheric level, but not necessarily what reaches your exact location. Light is filtered through various atmospheric layers before it hits the ground. This varies per location and with atmospheric conditions.

On an overcast day, when clouds filter certain wavelengths of light from the sunlight, the spectrum looks different. Generally speaking, we can say that daylight on a cloudy day has a more even spectrum-curve. This means the distribution of light intensity per spectrum section is more even, which increases our ability to perceive colors neutrally. This is important, for instance, if you want to judge the color of a certain set of house paints. Doing it on an overcast day will allow you to see the colors better than in direct sunlight, also because of less glare. The same goes for prints and other color sensitive applications. 'Daylight' is usually considered to be the direct light of the sun, plus that light which is scattered by the atmosphere (indirect). This indirect light enables us to see in areas where no direct light is present, as well as bouncing of light off of neighboring surfaces.

Energy

If we understand that electromagnetic waves are a form of energy, we understand that radiation in the infrared and ultraviolet ranges also contain energy, eventhough we cannot perceive them with our eyes. Infrared is generally perceived as heat, and ultraviolet as invisible radiation that may damage our health (UV radiation) but is also used for certain useful purposes by other animal species, such as by bumblebees for navigation. It should also be said that we don't fully understand all the effects of the electromagnetic spectrum on biological life. We do know that it's of vital importance to almost all living things and that life on earth has evolved in iteraction with the spectrum of our sun.

Why is this important if we want to learn about artificial light sources? There are various clues to be found in this as to the effects of various light fixtures that may not be easily explained from a purely technical perspective. In addition, understanding that visible light is just a subset of the electromagnetic spectrum is important to understand if you're looking for light sources that both perform well and are energy efficient.

Great spectrum diagram by Inductiveload, NASA.

In this guide we discern seven main properties of artificial light sources. Together these capture the most important properties of all the articifical light sources available, from the tiny LED in your stereo to large floodlights in a stadium. Some are more relevant than others in the discussion for good home and office lighting and will be expanded on in more detail.

The seven properties are:

• Spectrum
• Intensity and Energy Use
• Spread (light shape)
• Consistency
• Format, Fitting & Type
• Longevity and reliability
• Material use

Many of these properties are related to the technology used to produced the light. A short introduction of the most common types is in place here, with more details about each type further on in each section.

Type of lights

The type of light is determined by the technology used to produce the light. There's dozens of types, with a few common in household applications and others more suitable for industrial uses. The five most common light types in household lighting applications are incandescents, halogens, compact fluorescents, LED's and a few gas-discharge lamps.

In addition to this there are a few solutions that work on sunlight, which are preferrable over most artificial light sources, if they are applicable. The most common ones are reflectors and light tubes, but there are also materials which can store sunlight and emit it at night, for instance.

Halogens: Halogens are incandescent lights where the gas chamber is filled with a halogen gas type, allowing the light to operate at higher temperatures, last a bit longer, and be more compact. Halogens tend to be somewhat higher in performance than normal incandescents, with slightly higher efficiency, and a longer life span, but typically cost more. Halogens are also made in more accurate production processes that allow very specific models and light spreads to be made. Therefore, high quality spot lights tend to be halogen lights. Because of their excellent color rendering and spectrum, halogens have been the lamp of choice for demanding light applications in the home, office, laboratories and elsewhere. A halogen light bulb. You can see the secondary gas filled chamber inside. A common use for halogens: spots.

Light Emitting Diodes (LEDs) There are a few different LED types. We all know LEDs from the thousands of uses they perform as tiny signal lights on our stereo, phones, and other electric equipment. They are mostly semiconductor devices that operate on low voltage DC currents mostly, often requiring an adapter. Because they are semiconductors, LEDs are quite sturdy and less likely to break if dropped or due to harsh conditions compared to other lamps. Their life span is very long, some are rated up to 50.000 hours. LEDs used to only be available in red, green, yellow and white, with the blue type only becoming available much later. These signal LEDs (image below) are not suited for general lighting applications, because they are not very energy efficient and their spectrum tends to be ill suited for general lighting. It's been only recently that LEDs have been developed that provide decent general lighting. While the first attempts at producing generic LED lighting solutions proved to be somewhat disappointing -with many LED lights having extremely poor spectrum and lower than expected efficiency ratings- today there are ample high quality LEDs available that outperform most other light types in most areas. They are energy efficient, consistent, sturdy, have the longest life span of all consumer lights and can have very good light quality. The most common ailment of LEDs, especially cheap ones, are spectrum and color rendering, so keep an eye out on that. The light 'spread' may also suffer in cheap models. Also, for a long time it was not possible to produce LEDs that emitted enough light to replace a 60Watt incandescent light bulb. This is now also no longer a problem. LEDs tend to be a bit pricey, especially the quality kind. However, once you buy one, and don't, let's say, throw it around the room, it should last you a life time, providing great economy and worry free lighting. As with CFLs, LED lamps by default cannot be dimmed, but there are models available that do. Besides semi-conductor LEDs there are recent developments in Organic LEDs (OLED) and polymer LED (PLED) technology that are quite promising. Above: A set of commercially available LED lamps. Image by Geoffrey Landis. Above: A set of Power LEDs. Image by Gophi. Below: different types of signal LEDs. Image by Afrank99.

While most people in consumer situations don't pay much notice to the spectrum of the light bulbs they buy for in their homes, and instead choose lights by their intensity, the spectrum of light is the most defining characteristic of light sources. The spectrum defines the color, color perception, psychological effect and energy use of a light source. The spectrum of a lamp is usually a subset of the entire visible spectrum, which we can see when looking at a rainbow, or sunlight through a prism, for instance, where basic white light from the sun is shown in all its sub-wavelengths, and thus its colors.

Color and Spectrum

The color of a lamp results from the frequency of light the lamp is emitting mostly, or how it appears to an observer. It's very rare for a lamp to emit only a singular wavelength (color), which means lamps emit a range of colors even if it appears a certain hue (also when the light is filtered).

Usually there's a set of other wavelengths present in the light emitted, together called the spectrum. Light is what we call 'additive', which means that each color added will make the result closer to white. This as opposed to reflected light, such as with paint or printing, which is a subtractive process, where each added color will make the whole darker.

White light always contains a range of light colors (with at least some red, green and blue), and pure color lights have a narrow spectrum, or a peak spectrum. Light that looks white doesn't necessary emit the full spectrum though, as we'll see later in the guide.

Beyond Incandescents

If we're to choose a lamp which converts electricity to visible light efficiently, and doesn't 'waste' electricity by producing heat, incandescents are not a good option. This has resulted in a great many other light bulb types being introduced in the consumer market in the last decades, most famously the power-saving bulbs, or CFL's, and the more recent LED lights.

These new lamp types manage to save electricty by making sure there's as little energy spent emitting infrared and ultraviolet sections of the spectrum as possible, converting as much energy as possible in visible light. For instance, compare the spectra of an example LED, CFL and Incandescent lamp in the following diagram:

Diagram of the spectrum a LED lamp (blue), a CFL (green) and an Incandescent (purple) superimposed the solar spectrum (yellow). Note that the energy used by each lamp is at least the area underneath its curve.

The downside of this energy reduction is that some of these lamps have a very narrow spectrum, resulting in poor light performance for color rendering and negative psychological effects. The example CFl in the image above, for instance, has a terribly peaky spectrum that will make everything look ugly.

Therefore, a very energy-efficient light may not actually be a good light for its purpose at all, especially if it makes us sick when working in it for prolonged periods of time (seeing as the energy impact of medicine production in the western world is rather high). The trade-off between spectrum and energy savings, therefore, includes a consideration of the context in which the light will be used. A lightbulb for your garden shed might warrant a different type than that above your working desk. In some cases, an incandescent is still the right choice (for instance, for that garden shed it might be a good option, if never used long).

Color rendering

Our eyes can only perceive the color of objects if light that falls onto the object is reflected into our eyes. This means that if you illuminate a blue object with an orange light, it can be hard to see that the object is actually blue. It'll look very dark grey or black instead. Therefore, our ability to see color is entirely dependent on the spectrum of the light in the room we are in.

If not all colors are emitted by the light source in question in an even way, you will perceive a biased color set. This is important for those working with color sensitive applications, such as printing and design, but in general you want to make sure that the lights in your home have a pleasant spectrum. For example, skin can look strange under some compact fluorescents (CFL's) and some LED lights have 'dirty' looking light that make everything look old. Psychologically, a poor spectrum of light can influence our mood and our health.

In this visual simulation a perfectly blue blobthing called Edgar is set on a white pedestal, while illuminated with a white light.	Another visual simulation, where both Edgar and the pedestal are unchanged, but the light only emits red light. The result is a black Edgar, because his surface does not reflect any of the red light.

For a more useful example of quality of light spectrum and color rendering, here Edgar and the pedestal have received a color test chart paint job. The perfect white light shows all colors well.	In this simulation, the light is not perfectly white. While the white areas of the test chart still seem to be white, the color rendering of the whole is rather poor, and has dimmer, less vibrant colors.

Psychological Effects
The light spectrum also has psychological effects that can be hard to notice consciously, but have been proven to have long term effects on our wellbeing.

Light with a narrow spectrum, such as many fluorescents, besides having poor color rendering, may end up depressing people's moods and cause other psychological inbalances. Tests have been done on schoolchildren where standard tube lights have been replaced by full spectrum lights and not only their levels of concentration and moods went up, also their performance and general attentiveness. Flickering, whether noticed or not, also affects people's response to light. For more info on flicker, see further in the section about light consistency.

How to determine the right spectrum
First, you need to consider in what circumstance the lamp will be used. Will it be used often? Will heat be a waste or an asset? Will people work in the light? And so on. Then you can assess which spectrum and intensity you need, and the lamp's technology will follow.

There are various ways in which spectrum can be expressed to find out which lamp to buy. The most common way is by listing the light source's color temperature in degrees Kelvin. Typically, these come in three different temperatures: 2500-2900 (warm-white), 4000-5000 (white), 6000-9000 (cool white). You can refer to the chart below for a more accurate listing.

Temperature chart by Mifsud26

In general, color temperture listings say very little about the spectrum of the lamp. It says something about how you will perceive the color, but wether the spectrum is any good can't be said from a temperature listing. A 2800 kelvin CFL, for instance, may just have a peak at a orange color, and a smaller peak in the blue range, and the result is indeed warm white, but with a very narrow spectrum. Some manufacturers list the color spectrum profile on their website or can send it to you on request. That's the best way to gauge a light's spectrum, as it's not through some arcane index that may or may not tell you what you need to know.

If none of these are listed for a lamp you are investigating, there's unfortunately only one way to find out: buy a lamp and see how it performs. In that case you'll need specialized equipment to do a proper spectrum analysis, or you can just put it through its paces. To be honest though, if you are buying lamps you cannot find the spectrum information for from the company's website, you're asking for a poor spectrum. Cheap lamps from unknown origins will guarantee you poor performance in all areas. High quality lights mostly have spectrum graphs available.

How to affect the spectrum
Most of the time, we want a broad spectrum from our light source. But, in some cases, we only want a certain subset of it for particular purposes. This can be for setting a mood or an atmosphere, but also for certain practical uses such as in areas where light sensitive material are being handled (like in a photography dark room). It's not possible to extend the spectrum of a lamp using passive means, only to narrow it down. This can be done with either filtering or by reflection.

Usually it is done with filters. Filters sit in front of a light and just block out all the unwanted wavelengths, and let the rest pass. This is, of course, not very efficient. It's better to choose a lamp which is already very close or exactly the desired spectrum rather than throw part of it away. Lampshades also throw light 'away', but converting it into heat and blocking the actual light. While some light shades are important to keep from staring into the light source directly (which can be harmful for the eyes), too thick or large lampshades defeat the purpose of the light ficture in the first place.

The spectrum of light is affected by the surfaces it bounces from. If I have a blue wall, and direct a white lamp at it, I will get blue light reflected from the wall, filling my room. This is also the case with sunlight down a lightshaft or floor. If you want a room to feel warm, for instance, it helps to color one surface of the room -the one which receives the most direct light- a warm color, such as orange. This will have very strong effects on the perception of the space.

The intensity of a lamp determines the amplitude of the waves in the spectrum. Of course, the wider the spectrum, the more energy it costs to produce that spectrum. Because spectrum is not immediately apparent in most cases, it is possible for two different lamps which use the same technology to have very differing energy use.

The 60 Watt bulb

We used to buy lamps based on their wattage. Most people that grew up in the last century have a feeling for what a 40, 60 or 100 Watt lamp 'does'. This is based on the performance of incandescent light bulbs which, regardless of brand or type, used to perform somewhat uniform in all areas. Their spectrum was great, the enery input was a good measure of light output and they were cheap. They just broke a lot, but hey, they were cheap, right? The downside of expressing the intensity of a lamp with the amount of watts it uses is that wattage says nothing about how much light something produces, only how much energy it consumes. So, for energy efficient lights, a 10 Watt bulb may output as much light as a 60 Watt traditional incandescent.

In a way lumens are the light-equivalent to DbA (A-weighted decibels), the measure for sound pressure as perceived by the human ear. Since 2010 the European Union mandates that all light bulbs sold have to state their lumen output. Above you'll find a small chart listing some common light types and their typical lumen output.

You might find it interesting to know that there is a theoretical maximum to luminous efficacy, which, if you think about it, makes a lot of sense. Since light is a form of energy, there must be a situation in which all energy put into a lamp is emitted as visible light. This is generally considdered to be at 683 lm/W, and emits only green light at a wavelength of exactly 555nm, because our eyes are most sensitive for that wavelength.

Other aspects influencing energy use

There are some other aspects that may influence the effectiveness of your light source versus the amount of power it uses. Some of these are obvious, such as putting a light bulb in a place which blocks some of its light, such as behind colored glass, inside a lampshade and so on. Others are less obvious.

One of the most important losses of energy associated with lighting that is not generally noticed is the transformation losses that occur when using lights that use another voltage level or current than what comes out of our wall sockets, or for electronic ballasts. Incandescent light bulbs work directly off the domestic electricity network. However, CFL's and LED's usually require circuitry or a transformer to change that voltage to 12 volt typically, and also from alternating current (AC) to direct current (DC). This transformation is never achieved without energy loss, and when you have a poor transformer these losses may be substantial. It's therefore often better to have a single, high quality transformer than to have many little cheap ones. Transformers, especially cheap ones, may also emit a humming noise, and depending on its quality this may actually affect the quality of living.

For many modern lightbulbs that are screwed into traditional sockets (retrofits) the transformer is actually part of the lightbulb itself. In that case, and especially when the bulb is a high quality device, one may expect the transformation losses to be minimal. Still, the transformer does take away some energy, uses materials and in some cases quite toxic ones.

Age also influences electricity use. Not so much in that electricity use of a lamp goes up with age, but for CFLs and LEDs, light output diminishes with age, while electricity use does not.

Shown above is a light simulating showing three different light spreads, based on manufacturer's IES files.

The way light is emitted from a source can take many different shape or forms. The basic and most common spreads are the omnidirectional lightbulb, the simple spot and the tube light. These cover the majority of uses. There are others as well, for those unfamiliar with custom lighting, that introduce many new possibilities for quality indoor and outdoor lighting. Now that LED lights are becoming more common, more spreads are being introduced. It's worth noting that the spread of a good lamp is often achieved in co-ordination with the fixture the lamp is in. The best spreads are mostly achieved by a good lamp in an appropriate fixture.

In time, several lamp configurations have arisen that define the spread of light in various ways. These are mostly based on incandescents, but because other technologies are becoming more common, we see these transferred to CFL and LED more and more.

Simulating Spread

The spread of light is important enough for manufacturers to recognise that designers want to know how their lights behave when designing a space and/or lighting solution. Most manufacturers of high quality lamps and fittings therefore release digital files which describe in three dimensions what the spread of a particular lamp is. These files are often formatted as IES files, and they can be loaded by most 3D visualisation software to simulate the effect of the light on its surroundings. The top image of this section has been made this way. This is an excellent way to test lighting design before large costs are incurred. IES files are more commonly available for fittings than for lamps, though.

Some of the available standard spreads are:

Omnidirectional bulbs
These are the standard lightbulb that spread light in all directions, used for all kinds of purposes. With incandescents we're used to a perfect omnidirectional spread. For most CFLs and Gas-discharge lamps this isn't a problem either, although CFL's are naturally tubes, not spheres, bunching them up in spirals provides virtually the same effect. LEDs need to be arranged in a spherical pattern in order to achieve proper omnidirectional properties. Good LED lamps don't have a problem with it, but with cheaper models we've seen some issues with inconsistent spreads.

(Silver) Crown bulbs These lamps, which can be hard to find, are basically omnidirectional lamps with a silver coating on the top. They reflect the light back towards the rear of the lamp. This is usually applied in conjunction with specially designed fittings that then reflect the light forward again in a particular way. Several very high qualiy lighting solutions use this approach, because the larger reflector allows for more precision of the spread. All light types are available with silver crowns, but they may be hard to find.

Decorative lights You might have seen the candle- or flame-shaped lightbulbs in a chandelier in some tacky place. Those are decorative bulbs. They come in all sorts and sizes. These are usually not meant for proper illumination and mostly for effect, so do not expect great lighting qualities from them. As an accent in a space they can be used strategically.

The consistency of a light source determines both its consistency in spread and in time. Consistency in spread determines wether the light is spreading its spectrum in all directions evenly. With lights that have special spread shapes it's possible that some directions receive a different light spectrum than others. Spread in time mostly means flicker in the short term, and how the lamp behaves when it gets older.

Multi-color LED's, which produce white light by combining individual red, green and blue LEDs can have some interesting color effects in the fringes of shadows that may or may not be unwanted. This is due to the separate LED's being shaded at slightly different angles.

Consistency in time
Consistency in time mostly refers to flicker and aging effects. Flicker is almost always unwanted, although it can save energy, and aging effects are also almost always negative.

Quite a few lamp types flicker by design, most notably fluorescents. Any flicker above 60 hertz (60 times on/off per second) may not be directly noticed by the human eye, it is however perceived subconsciously and it can make eyes tired and cause psychological effects. Some people are more susceptible to it than others. As long as lights flicker at at least 60 Hz or more, they should not pose a problem for most people. Unfortunately fluorescents, especially older types, do flicker quite a bit. Only high frequency fluorescents eliminate this problem for its lamp type, but these are 'special' and thus more expensive. LEDs generally don't flicker.

Because of our electricity network's AC current's frequency of 50Hz in europe and 60Hz in the US most lights that work directly from the socket will have to deal with flicker one way or another. Incandescents did it by using a glowing filament that kept glowing for a bit after you took the power off. The short intervals between each power pulse was bridged by this glow effect. Other lights will solve this in different ways.

Light behave differently over age as well. Some, like incandescents and low sodium vapor lamps do not show any negative visual impact over age, which is a beneficial property. They just break when their time is up, and until then they perform like new. Fluorescents and LEDs tend to dim in time, where Fluorescents will eventually also break down, start to flicker and no longer turn on, whereas LEDs will continue to emit light at increasingly lower outputs for the same input.

The format and fitting of lights are mostly dependent on the application. There's hundreds of formats a lightbulb can take, from the ones in car headlights to those in stadium flood lighting. For household purposes, it's been common to use two or three fitting types, and about a dozen formats and stick to that.

In Europe these are mostly the fitting types E27 and E14 screw-fitting type and in North America the B15d and B22d bayonet cap fitting types are common as well. These fitting types are designed to allow easy and quick replacement of the bulb, and with thay show their historical usage for incadendescent bulbs that needed to be replaced often. Because CFL's typically last 10 times longer and LED's typically last the lifetime of the building they are in, it's not such a straightforward choice to stick to the old formats.

While the fitting type does not influence light quality directly, it does force a certain technological format. Because the fittings are supplied with power directly from the net they do not allow the efficient use of LED's without a built-in transformer. Therefore, when constructing or renovating a space, it's best to choose different solutions for lights, based on low voltage DC currents that end up saving a lot of electricity and provide high quality of light for the duration of the structure. This can be achieved by building-wide DC networks that have been available for some time. Besides lights, they can also power most household equipment without a transformer, such as laptops, phones and so on.

Click on the image below to zoom.

Common base / fitting types:

We've mentioned the reliability of most light types above, but it's good to reflect a bit on the topic in general. Lamps are usually listed to have a life span of a certain amount of hours. However, the conditions and pattern of usage may have a large influence on this life span.

Life span of CFLs
CFLs have as a standard life span about 10.000 hours. Depending on the make and model it will reduce in light output towards the end of its life and eventually stop functioning altogether. Fluorescents, indlucing CFL's, tube lights and others, can have a severely diminished life span if they are switched on and off often, for instance, sometimes even lower than incandescents. There are special models thart are used for rapid switching. It is suggested that a CFL is better left on if a room is left for less than 15 minutes. A 5 minute on-off cycle used occasionally may already severely deteriorate its lifespan.

Besides LEDs, most light types break reasonably frequently.

Replacement maintenance
We've become very used to light types that break occasionally requiring someone to go up to the light fitting and replacing it by hand. It seems to be the most common thing in the world. However, imagine a concert hall, with lights sitting dozens of feet above the audience, or in large public spaces, where lamps can be far away and hard to reach. Most lamps that are currently used break eventually and while building these buildings and structures it has been taken into account that the lamps might need replacing every now and then.

With the introduction of LEDs this may change. Because LEDs outperform most light types, especially for general lighting, and because LEDs have much longer life spans, they can potentially save a lot of material, energy, money and maintenance effort. We can design buildings where lights are embedded within the building to provide a range of interesting and exciting lighting solutions. The division between luminiere and light source, something we've become so used to, can disappear. A well designed lamp can not only hold a light source but be the light source, opening up a world of exctiing lighting possibilities.

A few words on material use. We're used to the material use of lights to be rather benign both in amount and nature. Incandescents are really not much more than a bit of glass, some thin metal and a glowing filament made of harmless Tungsten.

Not so with some other light types, however. As the energy saving became more important, the CFL has been introduced in our homes. CFLs, other fluerescents and some gas-discharge lamps contain significant amounts of mercury. Mercury is a neurotoxin that is extremely poisonous to all living things, and is also bio-accumulative, which means it stays within the body. While it is true that the energy saving that CFL's represent also reduce the mecury output of some electricity plants, breaking a CFL or mercury vapor lamp will introduce a concentrated amount of mercury into our living environment, which is the most dangerous distribution of the toxin. If you break a CFL, get everyone else far away from the room, open the window and clean up the lamp as quickly as possible. Don't use your bare hands and don't use a vacuum cleaner to suck up the pieces, as it will blow out the mercury into the room. Read this to know more about what to do if a fluorescent lamp breaks. If mercury containing lights break down, please bring them to your hazardous waste collection point.

LEDs also contain some toxins, but usually far less and less toxic materials than Mercury. With some LED systems, however, the separate adapter cannot be disregarded. This is virtually the same adapter type as we're familiar with for Halogen spots, and are quite substantial in their material use. This can be avoided by installing a central power converter in the house. The adapter generally lasts beyind the life span of the lamp, and can be produced quite compact, reducing its material use, as seen in modern LED refit models that can be put in a traditional socket.

If LEDs break down, also bring hem to a chemical waste disposal facility.

The cost of ownership of a lamp extends beyond the purchase, maintenance and energy consumption costs. Because light is vital for us as biological creatures, the quality of light might affect us in ways which may allow us to perform better, be healthier and in general more happy. Of course, saving energy also helps save the envionment, which is currenty costing our governments a lot of resources as well.

These important considerations are difficult to capture into numbers, so if we consider high quality lighting as a basic necessity and understand that this has added value in the long run, also financially, it should be understood that sacrificing light quality will cost us in the long run. In addition to this, we can use the purchase, maintenance and consumption costs as an indicator of our financial investment, which comes out in our favor in the long run as well.

Below we've made a simple comparison of the cost of ownership of generic Incandescents, CFLs and LED lamps for a 10 year period, ~6 hours a day (22000 hours), at a cost of € 0,20 / kWh, which is accurate for spring 2011 for the Netherlands. These are reasonably generic lamp values taken from off the shelf store bought items.

As we can see, the CFL and the LED are both considerably cheaper to operate than incandescents. The difference between the LED and CFL are minor, depending mostly on wether the second CFL will make the 22.000 hour mark or break before. The LED does give a better spectrum during this life span, and can continue to operate for quite some time after the 10 years use therefore the LED is the cheapest option alltogether. Note that neither the CFL or the LED reach the lumen output of the incandescent, while both are officially rated as 60W incandescent equivalents.

Because these values may vary quite a bit, it's best to do this calculation again once a number of eligible light sources are found to see which one comes out best. For equivalent cost, the light with the best spectrum and consistency should win, in addition to considerations about health.

We've performed many experiments with light types over the years, predominantly with LEDs. We see LEDs becomming the light source for the next century. Our experiments range from soldering together dozens of signal leds to see what their performance would be (poor), making all of our own lamps for our offices to trying to assemble the most energy efficient light available. We've seen quite a few good and bad examples of LEDs for various purposes. Some of these stand out, and we'd like to show you a few of them.

Very cheap LED lamps
It's so attractive: a lamp that will last 50.000 hours, has a great spectrum, does not flicker and is very light efficient. And if you see one that's cheap in addition to this, it's hard to resist. It sounds too good to be true, and in our experience it always is. Cheap, often chinese made, LEDs are better left in the store. Mind you, there are excellent Chinese made LEDs available, but the unbranded cheap ones usually have 'made in China' on them, and perform poorly. Thankfully, they're somewhat recogniseable, no matter where they're from.

We've had quite a few cheap LED lights that fit right into a standard light socket (retrofits). Some of these perform well, but we've found that some of them do not reach their advertised ratings, their energy performance is poor, their spectrum very unattractive and in general do not pose an attractive package, not even for their price. One type that stands out is the multi-LED type, in which a group of 10+ signal LEDs are combined in a single casing, usually without a dedicated lens. As with our own experiments, these lamps basically combine a large set of very cheap signal LEDs to produce enough light. And as with our own experiments: it doesn't work. Because signal LEDs are cheap, as they've been around for a long time and are produced in very large masses, the cost of these LEDs can be low. Dedicated general lighting LEDs, a subset of Power LEDs in general, are expensive because they're harder to make and their development has been only in the last decade. Since these lamps are essentially one big signal LED, and given that signal LEDs are very poor general light sources (except for flash lights and such), so are these lamps. The light spectrum of these lamps is very narrow and the light tends to be on the dirty side of things (yellowish, cold, etc). Their color rendering is very bad. Their spread, due to the lack of a proper reflector and/or lens is dismal. We retain one of these in our office to show the result from a bad LED. For a little bit more money one could buy spots made from three powerLEDs. These have a much better spectrum, energy usage pattern and they look better as a light as well.

Above: Steer clear of these, if you can.

Single Power LED spots If you were looking for a nice general spotlight and buy one of these, you might be looking funnily at your purchase once you start using it. These spots have a single power LED with a clear, very round lens. While these spots have their uses in specific cirumstances, their hard spread, which is more akin to a stage-spot than a spot for home or office use, casts sharp shadows at any distance and has a rather crude cutoff. This is somewhat inherent to its design. LEDs are point-light sources that require some sort of mediation to have a nice spread, either though a very good lens, a reflector, multiple leds together and usually a combination of those three. Single power LED spots seems to want to cheat on this, and we have not seen a good result from these yet. Let us know if you find one that does, though.

A single-LED with clear lens spot.

AC driven LEDs We've encountered some LEDs that can be driven by wall-socket current without using an adapter. We purchased some of them, and while their efficacy was not brilliant (50-60 lm/watt), considering there are no other power losses in a driver or transformer, this is actually rather good. Their spectrum is some of the best we've seen next to incandescents and they provide new freedoms we didn't think possible. Even their spread is rather nice for an on-die LED. They save a lot of material and energy by not requiring an adapter and become more reliable as well. The best example of these are the Acriche LED range. As far as we're aware, these are the only AC LEDs available. These single power LEDs can be bought in on-die form and then used in whichever application suits you. In our case, we've used them as general lighting in the office, at home and are considdering various lamp products with them. Making them work with dimmers is a bit of a challenge, but not impossible. One of the interesting things we found is that they manage to get this to work by actually including two LEDs in one light. Because AC alternates its current, and LEDs are diodes and only work when the current flows in one direction, the two LEDs take turns pulsing light one each side of the current sine, together producing a steady 100 or 120 Hz, which is more than ample to remove any semblance of flicker even for people sensitive to it.

An Acriche AC driven LED