Why It Matters that Artificial Light is Not Like Daylight

My brother is prone to Seasonal Affective Disorder (SAD). When he doesn’t get enough exposure to daylight, he becomes horribly depressed. Typical artificial light does not help because it does not give him enough of the wavelengths of light that combat SAD.

Every winter morning, he spends 20 minutes or so reading the newspaper under a special very bright lamp that produces light similar to strong sunlight. That is the way to treat SAD, and it works.

He is not alone. University researchers in Scandinavia tell me that without enough exposure to sunlight (or a close imitation), about 10% of the population is vulnerable to extreme SAD like my brother’s.

The incidence of mild SAD is more variable and depends heavily on latitude. In southern Europe, just the most vulnerable 10% tend to develop SAD. In northern Europe, about 40% of the population develops SAD to at least some extent during the winter, with 10% of the population getting it badly.

I live in England. Although I’m not nearly as vulnerable as my brother and never had much difficulty with it before, here I do feel it a bit. To combat SAD, I use special full spectrum (also called daylight) bulbs in the rooms where I work during the day.

Unfortunately, even full spectrum artificial light is not strong enough to help your body make enough vitamin D to keep you healthy. You can take tablets for that. But the most effective treatment for SAD is enough of the right kind and intensity of light.

What’s Really Important about LED vs Fluorescent vs Incandescent / Halogen

It has become fashionable to sneer at incandescent light bulbs as energy hogs that don’t even provide very satisfying light. It is also fashionable to tout compact fluorescent bulbs as the current state of the art for combining energy savings with good quality light. LEDs are even more efficient, but leave most people feeling dissatisfied with the intensity or the quality of their light.

That is too simplistic a view, missing important strengths and weaknesses of each light source.

Incandescent and Halogen Light

Incandescent bulbs work by running enough electric current through a wire to heat it up to the point where it glows. Think about hot glowing steel on a blacksmith’s anvil, and you understand the concept. Most of the energy spent in the light bulb goes toward heating the wire, not emitting light, so it is very inefficient. There is an upside, though. When you plug it into alternating current, the wire does not cool off much during the fraction of a second when the current is switching directions. The wire continues to glow and any flicker is too negligible for your eyes to detect.

Halogen bulbs are a special type of incandescent bulb. An incandescent bulb contains a vacuum to prevent the hot wire from burning up. A halogen bulb contains halogen gas. When the gas gets hot enough, a chemical reaction called the halogen cycle starts occurring. The chemical reaction releases additional light. This is why halogen lights are so intense and so hot—to run the chemical cycle, they need to be hotter than ordinary incandescent bulbs. Their colour temperature is higher than an ordinary incandescent bulb, so their light is somewhat more like daylight. (In fact, if they are not made with appropriate ultraviolet blocking features, they emit UV and can cause sunburn!)

They are more efficient than incandescent bulbs but not as much more efficient as fluorescent or LED lights. Their extreme heat can ignite fires if they are not properly mounted.

Halogen bulbs are delicate to handle. Any surface contamination such as body oils in fingerprints can cause a damaging hot spot on the quartz envelope of the bulb when the bulbs heats up. Ultimately, this damage can cause the bulb to fail or even explode. Halogen bulbs should be handled either by their porcelain base or by using a clean cloth or paper towel to protect the bulb from contact with the skin. If the bulb’s quartz envelope does get smudged, it should be cleaned and dried before it is used. Surgical spirit (rubbing alcohol) is recommended for cleaning.

Needless to say, both incandescent and halogen need to use extra energy when they start just to heat up to the point where they emit decent light. But they heat up so quickly, they appear to turn on instantly.


Fluorescent bulbs require a tube coated with phosphor, and containing mercury and a small amount of an inert gas such as argon. An electrode is at each end of the tube. When the electrodes are oppositely charged by a sufficient voltage, electrons pass through the gas from one electrode to the other. Mercury has been lying in the tube as a liquid, but the current passing through causes it to vaporise. Electrons and charged atoms of gas begin to collide with molecules of mercury gas, which emit light.

Mercury emits mostly ultraviolet light, which is not what we need for room lighting. This is why the tube is coated with phosphor.

When phosphor is hit by light, it emits light, although not quite as much as what hit it. (Some energy is wasted as heat.) That might seem like a complete waste until you realise phosphors generate light in the visible spectrum. By hitting phosphors with ultraviolet light that we cannot see, a fluorescent bulb creates light that we can see. The exact mix of colours (or Kelvin temperature of white light) produced by a fluorescent is determined by the exact mix of phosphors used to coat the tube. Phosphors can be chosen to produce a spectrum close to that of sunlight.

Like incandescent and halogen bulbs, fluorescent bulbs cannot work below a certain temperature. The mercury inside them has to be able to vaporise. Even in normal environments, there is often a slight delay before they reach full operating temperature and produce light that matches their rating. But they do not need to get nearly as hot or waste nearly as much heat, and they can operate much longer before they fail.

They take longer to reach operating conditions, to the point where the delay before they produce good light is often perceptible. When they are colder than room temperature at startup, it can take a few minutes for them to achieve normal light output. They also need an electrical device called a ballast to convert standard house power into the strong differential necessary to run them.

Comparison with Light Emitting Diodes (LEDs)

LEDs, discussed further below, are rapidly becoming more efficient and commercially available. LEDs may surpass fluorescents soon (might even do so while you read this). However, right now the most efficient lighting you can buy is fluorescent—long straight bulbs about five to six feet (almost two meters) long. Shorter tubes are not as efficient. Tubes that are curved or bent are not as efficient. Tightly curved compact fluorescent bulbs are not as much easier on your electric bill as marketing literature would have you think.

Obviously, the mercury in fluorescent bulbs is toxic. When fluorescents fail, they should be disposed of as hazardous waste. Many people just toss them into the rubbish bin (trash can) so they end up contaminating landfills.

A small portion of the population feels somewhat ill under fluorescent lighting. For one thing, some of the ultraviolet light from the mercury leaks through along with the white light from the phosphors. People whose health conditions make them vulnerable to ultraviolet can find that sickening.

In addition, alternating current causes fluorescents to flicker. It happens so fast that most people cannot consciously detect it, but at a subliminal level your brain notices. Some people have difficulty with it. As an example, flicker can escalate my migraine headaches from merely bad to incapacitating.

Light Emitting Diodes (LEDs)

A light emitting diode is a solid state device that emits light when given electric power. LED “lamps” can be big enough to look like small bulbs or hardly bigger than a pinprick. Each LED emits only a little light, so a number of LEDs need to be combined to get enough intensity to make a worthwhile lighting unit.

Unlike the other types of lighting described here, LEDs do not need to get hot in order to work. Indeed, they need to be kept within a reasonable temperature range, neither terribly hot nor terribly cold, so they actually need to have heat that they generate pulled away from them. They truly do turn on instantly without any need for a surge of extra power to reach full operation.

They can run at reduced power (to dim their intensity) with little or no shift in the colour they emit. Halogens and fluorescents cannot be dimmed much, if at all. Incandescents shift toward the red end of the spectrum as they are dimmed.

LEDs also run on direct current at a low voltage, not on alternating current at a high voltage, so they don’t flicker. Whether or not you can see it, LED lights plugged into ordinary household electricity always include a device that converts the electricity to what they need. LEDs running at their naturally favoured voltage are very well suited to low voltage solar power.

In theory, LEDs should be dramatically more efficient than incandescent or fluorescent lighting. By the time such things as the power converter and the number of LEDs necessary to get the desired amount of light are added in, LED lighting efficiency on household power is comparable to fluorescent, but long straight fluorescents still have the edge. LED efficiency is improving by leaps and bounds, though, especially in the past couple of years.

However, each LED naturally emits light in just one colour. The colour is not as pure as from a laser, but it is relatively pure. So-called white LEDs are really blue with a dab of phosphor on top. The result is white light plus a large spike of blue that leaks through from the LED. Compare the light emitted by one model of Luxeon ™ brand DS64-12 white LED with the black body radiation curves in Part 1 for daylight and other common types of lighting.

Luxeon White Spectrum

The exact parameters to describe other white LEDs vary slightly, but the general shape of the curve is very similar. This is why light from white LEDs does not quite look right. For people who have trouble with fluorescents because of flicker or leaking ultraviolet, this is a vast improvement even though it isn’t quite like daylight.

You will see some merchants offering LED lights that combine red, green and blue (RGB). That’s a step in the right direction, but it only provides complete coverage of the visible spectrum when the light is displayed into your eyes, as from a television screen or computer monitor, rather than illuminating something you want to see–so even that artificial light isn’t quite right.

The next page should round out your basic understanding of what’s missing in artificial light, so you’ll know what has to be coming in next-generation lighting.

Click to read more…    Page 1    Page 2    Page 3

Further Discussion

We are at the awkward point where new technology is emerging rapidly, and you can find some really good new lighting available to buy. But a lot of junk is also out there in the marketplace. With any new technology, it takes a while before everybody comes up to speed about how to handle it.

When I find something I feel is worth mentioning, I post about it. Click here to see those posts.