Lighting 101
This web tutorial describes the terminology used in lighting, describes how the human eye perceives light, and what type of lighting would work best for your project.
Lighting Terminology
Watt – A quantifiable measure of power consumed
Lumen (Lumen) – A quantifiable measurement of total power of light emitted
Foot Candle (FC) – A unit of illumination of one square meter which is one meter away from a uniform light source
1 FC = 1 Lumen / Square foot
Kelvin Kº (colors of light) – measured in degrees, is a quantifiable measure of color temperature
Min – Minimum amount of light
Max – Maximum measurement of light
Uniform – Lighting that has even illumination across an area with a low min to max lighting ratio
Spacing – measurement of space usually in feet from one light pole to the next
Color Rendition Index (CRI) – a way to asses how light sources make objects appear. Any CRI greater than 80 has good color properties
Average Rated Life – referred to in lamp life is actually the median
Mounting Height – the measurement from the ground to the light source
Distribution (I-V) – Determines how far light is emitted to each side of a fixture and to the front (street side) and back (house side)
- Type I – long linear pattern, long distance to the sides with a short pattern out to the front and back
- Type II – Progressively growing distance to the front and back and shortening of the linear sides
- Type III – most commonly available in most fixture types has a perfect oval shape
- Type IV – has a more circular pattern with linear sides that extend farther on the sides
- Type V – Round circular pattern same distance from front to back and side to side
Optics for Streetlights – control of light distribution
- Non-cutoff – light is emitted in all directions
- Semi-cutoff – most of the light is emitted below 90 degrees
- Cutoff – controlled lighting where less then 2.5% of the light is allowed to escape the fixture above 90 degrees
- Full-cutoff – used in dark sky friendly locations, optics put the light on the ground below the fixture not allowing light to emit above 90 degrees
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Anatomy and Physiology of the Human Eye
Light enters the eye through the pupil and the retina focuses and transmits the information we see to our brain through a nerve which allows our brain to process the visual information. It is hard to describe lighting and illumination as each person’s sight and what they see is subjective.
The actual measurement of light must take into account the way that the eye is programmed to see, and for our purpose, programmed to see light at night.
The retina is made up of cones and rods. The cones create a synapse which allows humans to see detailed central vision (color), to read, and to see objects for security. The rods are highly sensitive to light, allowing them to respond in dim light and dark conditions; however, they cannot detect color.
When referring to human sight under light at night, we must keep the color of the light close to a natural color and provide just enough light so that the cones are still activated to see objects. If the light is too bright, the retina will naturally close up and the cone cells will not be activated, not allowing the human eye to see objects clearly. In addition, if the light is yellow the human eye will not be able to perceive the correct color of the objects.
Therefore, SEPCO™ lighting takes theses factors into consideration. SEPCO’s system uses the best lamp color to allow the perceived color to be to the truest color. We also provide uniform illumination at a level that is comfortable and allows the eye to naturally focus and not squint. We use the perfect illumination levels and a low min to max ratio which creates a nice even illumination.
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Fluorescent Lamps
The advantages of theses lamps are they provide higher efficacy (lumens per watt), longer life, and cooler operation. The light is emitted over the length of the bulb. Their efficacy is 4-8 times that of the filament sources. They can provide over 20,000 hours of life and are economical.
These lamps are available in many shades of white color. Depending on the application varying color of light output can be chosen. Turtle friendly applications can use an orange-yellow color. Lighting to match the color of other electric powered lights can be yellowish. Our standard lamp color is pure white, called 5,100 degrees Kelvin. Other types are not as popular, such as the 6,500 degree Kelvin lamps which are brash, bluish white that humans find offensive. |
