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Friday, October 03, 2014

Perception is Reality (Oct 3)

UAS Construction Update for 10/03/2014

Perception is Reality

What we perceive to be real, is frequently not factually correct.  The new UAS LED lights are a good example.  Most new street lights, including the UAS parking lot lights are considered a full cutoff light which directs the light down to the ground and prevents light from escaping up above the light fixture.  Because you cannot see a full cutoff light from the side, your mind perceives that the area is not as light.

Standing in the upper UAS parking lot looking back at the lower parking lot lights you notice that the lights become less visible.  This is one benefit of full cutoff lights.

UAS Parking Lot with Full Cutoff Lights

Parking Lot Lights


The International Dark-Sky Association has been working with communities for the past two decades to reduce light pollution. They recommend Full Cutoff lights as one is one tool to reduce light pollution.  Light pollution is a broad term used to describe multiple lighting problems.  I like to think of it as artificial light shining in places you do not want.  Light Pollution to Night sky gazers is light that shines up into the sky creating skyglow making it difficult to see the stars.  Light Pollution to residents is light that shines into your home or bedroom making it difficult to sleep.  Light Pollution to motorists is light from a fellow motorist with xenon headlights or adjacent commercial properties with distracting over bright lighting.  Light Pollution to a camper is the other camper wearing a headlamp who blinds you with 120 lumens while telling you stories of past adventures.

Northern Lights

Northern Lights


While full cutoff lights will help UAS Freshmen to see the northern lights better, they can present problems with pedestrian perception.  People walking along a road or pathway at night tend to look up toward the next light they can see, which could be light from a house or a faraway street light. They perceive how dark the pathway they are walking on more by that light in the distance, than the light immediately surrounding them.  For an Engineering example: Take two pathways and using full cutoff lights and a light meter, light both paths to 1.0 foot-candles.  Then take a bright light and place it at the end of one of the long paths.  Because the light at the end of the path is far away and not shining on the path the light meter on the path will still read 1.0 foot-candles.  Now take your normal test subject and have them stand on each of the two pathways and have them tell you which one is brighter.  They will always say the path with the light at the end is much brighter.

This presents a challenge for using full cutoff lights for pedestrian pathways because even though there may be enough light shining directly on the path to safely walk, (0.5 foot-candle) the person looking down the path cannot see the light coming from a full cutoff lights and will perceive that the pathway is dark and unsafe.

New UAS Pathway Lights to Soboleff

Pathway Lights to Soboleff


The new pathway lights installed on the pathway down to the Soboleff Building have a mounting bracket below the LED light which deflects enough light that you can see it from the end of the pathway.  With this type of light fixture, we will see a trail of lights stretched before us and our minds will perceive that the pathway is lighter, even though my light meter tells me it is the same J

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