The Basics

Ever wondered why artificial light never feels quite right? By reading below, in just a few minutes you can come to understand why. You don’t need to be a tech wizard to understand.

The Visible Spectrum

Energy has a wavelength and a frequency, which are related–as the wavelength gets bigger, the frequency get smaller, and vice versa. You may be accustomed to thinking of radio in those terms, but the concepts really apply for energy beams in general.

Science classifies energy in terms of its wavelength. Radio is in one range of wavelengths. X-rays are another. Visible light wavelengths range from about 400 nm to 700 nm, like so:

Visible Light Spectrum

Visible Light Spectrum

The longest wavelength appears red, which is the lowest-energy visible light. Although the shortest wavelength, highest-energy visible light is violet, by convention that end of the spectrum is usually called the blue end.

Sometimes infrared or ultraviolet wavelengths are also desired from artificial lighting. For example, heat lamps generate some infrared light. When those wavelengths are included at each end, the result is the extended visible spectrum.

Many Shades of White Light

What people call white light is a combination of wavelengths of light. Daylight is a strong, smooth blend of wavelengths in the visible spectrum–our eyes have adapted to fit it. But term white light covers a wide variety of mixtures of coloured light. Not all white light is the same.

Since the term white light is vague, we need a way to describe different variations. This is done by measuring the color temperature (also called Kelvin temperature) of white light.

Scientifically, color temperature is the color of a light source in relation to a black body at a specified temperature expressed in degrees Kelvin (°K). In common language, it is the visual warmth or coolness of a light source, separate from the physical temperature of the source.

  • High color temperature white light is cool, shaded toward the blue end of the spectrum.
  • Low color temperature white light is warm, shaded toward the red of the spectrum.

How Daylight and Artificial White Light Differ

These figures are general. It is possible to get special light bulbs the emit an atypical flavour of white light, although artificial light simply does not quite mimic daylight.

  • The color temperature of daylight is high at nearly 6000 °K, so it is cool and bluish.
  • Halogen light is somewhat warmer at about 4100 °K.
  • Typical incandescent lights have a low color temperature of about 2800 °K.

By now, you should have a glimmer of understanding about why artificial light never quite feels like daylight. Scott Roberts publishes data and a graph at his website to help this make sense. Click here if you want the data for his graph which is below.

Black Box Radiation

Black Box Radiation

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.