When deciding what type of lighting to use, most designers don’t think twice about the physics behind light, and rightfully so. However, having a basic understanding what light is, how it’s produced and how it’s analyzed, can prove useful when it comes to choosing the right lighting for the job.

As a lighting designer, you’re mostly interested in the following main parameters when choosing lighting:

  1. Type of light source
  2. Fixture output wattage
  3. Fixture type and distribution
  4. Luminous flux (unit: lumens)
  5. Luminous emittance (unit: lux or foot-candles)
  6. Correlated Color Temperature (CCT) (unit: kelvins)
  7. Color Rendering Index or Color Retention Index (CRI)

Luminous Emittance, commonly referred to in the industry as the “light levels” or “lux levels”, is the key parameter designers must meet.  Most clients will have design standards that define the required average lux level for given areas. As such, most designers make this their primary focus, choosing fixtures that can meet the required lux level, failing to weigh in some of the other key parameters.

Light and Color

Without going too much into the physics, light is an electromagnetic wave. A common property of any wave is its wavelength measured in meters. Wavelength is in fact inversely related to a wave’s frequency, a term which we have all heard of before and is more commonly used. A wave with a high frequency has a shorter wavelength. Likewise, a lower frequency wave has a longer wavelength.

 

wavelength

Electromagnetic waves exist in a vast range of possible wavelengths, from large wavelength (low frequency) radio waves to short wavelength (high frequency) gamma waves.

 

electromagnetic-wavelength-spectrum

When we talk about “light” in laymen terms, we are actually referring to electromagnetic waves within a specific range of wavelengths. This is what’s known as the “visible light” range, and is the range of electromagnetic waves that our eyes can process as colors.

human-visible-light-spectrum

A key concept to grasp is that without light there is no color. Try standing in a pitch dark room and try to distinguish objects of different colors, it won’t work. We see colors because objects absorb and reflect light back to the environment. If there is no light source, there is no color. Different objects, due to their different properties and makeup, reflect light at different wavelengths. The human eye (and brain) has evolved over the course of nature to allow us to interpret different wavelengths as different colors. The object may in fact reflect electromagnetic waves outside the visible light range. Some objects may emit UV radiation, however the human eye is unable to process that information as color.

 

flower-uv-light-bee-vision

The images above shows how a bee would see a flower. The bee’s vision has evolved in a way such that it is able to see UV light, helping it find nector and pollen within a flower. This is different from the way the human eye has evolved.

As we said earlier, without light there is no notion of color. We require illumination with a suitable source of light in order to be able to distinguish colors. Thus we come to the conclusion that the source of light can affect the color objects, or at least how our eyes perceive it, which is all that matters. Various light sources have various spectral power distributions. Some light sources emit only certain discrete wavelengths of visible light while other sources emit the entire visible light spectrum (white light). This leads us to our next article on the Color Rendering Index (sometimes referred to as the Color Retention Index) and the Correlated Color Temperature (CCT) of a light source.

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