Vision provides us with most of the information that we rely on to survive, and vision would not be possible without light. Light is the stimulus for vision. The receptors in the eye only respond to electromagnetic energy between 380 nanometers (nm) and 760 nanometers (nm). The difference between x-rays, radio waves, UV, IR and visible light is their wavelength. When light travels through a prism the speed at which it travels slows down and the light waves are bent and refracted at different angles so the light emerges as a fan of different colors. What we see as colors are the colors in the light. A blue wall is blue because the light source contains wave lengths in the blue part of the spectrum.
Since light is such an important factor in all our lives it is essential that the environments that are created by lighting designers must allow the eyes to function at optimum levels for the psychological and general well being of the inhabitants. That is the reason you must take control of your lighting. Learn as much as you can about proper lighting so that you will be able to direct the installation of that lighting. But if you do not want to take the time to do that, hire a trained lighting professional to represent your interests. Get the lighting you want and need. The difference between good and bad lighting is huge and will impact your life for years. Budgets are tight, but do not skimp on the lighting…it is what enables you to enjoy everything else in your house.
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We do not see light directly unless we look directly at a light source. What we see is light that is reflected off a surface. If something appears brighter than something else it is because of the difference in contrast between the two objects. This is referred to as relative brightness and it is important to proper lighting design as we will discover in future postings.
|Driving at Night|
One of the most common examples of relative brightness is the automobile headlight. Have you ever been blinded by super bright headlights? That is because the eye’s pupil can not adjust fast enough when going from total dark to really bright. This is especially problematic for older eyes.
Reading is another example of relative brightness. Reading black type on white paper is much easier than reading navy blue type on blue paper. That is because the black/white contrast is much greater than blue/blue. Even in moonlight the contrast between black type and white paper makes reading possible.
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Before my first posting about light bulbs (sources of light) there are some qualities of light with which you should become familiar. Different sources of light exhibit different characteristics that influence which light bulb to use in different situations.
Color Temperature is a term that refers to the color of light, commonly expressed as warm or cool. Technically it is expressed in degrees Kelvin (K) with lower numbers being warmer than higher numbers. For example 1,700K is the color of a flame, 2,700K is the color of an incandescent light bulb, 3,000K-4,500K is the color temperature of fluorescent and LED light sources and 6,500K is the color temperature of the sun on an overcast day. For residential lighting purposes most color temperatures are compared to incandescent light.
|Notice the smooth transition from
red to violet for the
incandescent light bulb.
Color Rendering Index, expressed as CRI, is a measure of how good colors look. All light bulbs are compared to an incandescent light bulb which is deemed to have the best CRI. CRI is expressed by a number from 1 to 100, 100 being the CRI of an incandescent light bulb. CRI’s between 82 to 100 are judged to be satisfactory while CRI’s below 80 are not. Most of the new fluorescent light bulbs, including CFL’s, are mid 80 or higher. LED’s currently range from about 65 to 88. In the photo to the left you can see the full spectrum in the light of the incandescent light bulb earning it it’s 100 CRI rating.
As humans our eyes see color as the reflection of the color in the light source. If part of the color spectrum is missing from a light source, red for example, you will not see red. Some of the early highway lighting had such bad CRI that at an accident scene the police could not differentiate between blood and oil.
There is a lot to learn about light, how we see light, how contrast affects how we see, how glare interferes with our vision and what kind of light is best for different situations. I strongly urge you to download the Underwriters Laboratory app “Light Smart” at the App Store. It has lots of great information about lighting.
Please visit my website, FoggLighting.com.