Standard Lighting Terminology
Watt –A quantifiable measure of power consumed
Lumen – A quantifiable measurement of total power of light emitted
Foot Candle (FC) – A unit of illumination of one square foot which is one foot 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 assess 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 than 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
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.
SEPCO solar lighting systems takes these 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.