Scotopic vs Photopic Vision: How Your Eyes Perceive Light Quality

Posted by Jimmy Hovey on Thu, Oct 24, 2013 @ 08:10 AM

Scotopic vs Photopic Vision....How to Interpret What Your Eyes are Telling You

What's lighting quality?

Lighting quality is not as simple as taking a light meter and getting high foot candle readings. Unfortunately high foot candles do not mean the lighting is right. You can have lower foot candle(we'll call them FC) readings than before a project and actually have better light.

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How the human eye percieves lighting is far different than how a light meter percieves it. BETA, a manufacturer of LED lighting has done a fantastice job of summarizing what it means.

What Is The Difference Between Scotopic and Photopic?

An important factor in measuring LED effectiveness is understanding the difference between Scotopic and Photopic vision in relationship to how the eye perceives light. (What is Scotopic and Photopic Vision?)

Seeing is believing: A recent study comparing the public’s perception of 100-watt HPS lighting vs. 75-watt LED lighting dramatically demonstrates the superiority of scotopic luminance. Scotopic vs. Photopic in Action: The Cree Garage Lighting Survey

Intel Tests Scotopic vs Photopic Vision

An experiment at the Intel Corporation’s multi-building campus in Hillsboro, Oregon, proved the scotopic-photopic theory. Described in Dr. Sam Berman’s article “The Coming Revolution in Lighting Practice,” Intel facilities staff observed during the study that one could see better under the scotopically rich lighting, and that this lighting was actually perceived as brighter even though a traditional light meter would indicate the opposite.

Intel realized they would achieve larger energy savings by reducing the number of lamps needed while at the same time improving overall lighting perception and effectiveness. In the campus’s eight buildings, scotopically enhanced lamps have yielded annual lighting energy savings of slightly larger than eight million kilowatt hours.

Footcandle Readings No Longer Enough

Light meters see light as photopic, however with the color rendering of todays newer lighting technology that is not always enough. That is how we can have a lower FC reading on a meter and yet to the human eye, the area is significantly brighter. The human eye is a far better "light meter" than any little gadget.

We Have Seen "The Light"

We have witnessed this first hand on one of our projects. We replaced 1000W metal halide fixtures with 250W Inductive fixtures.

The results?

The light meter said that there was less light. The human eye said not only is there more light, but the colors look more accurate as well.

How Does Scotopic vs Photopic Relate to Energy Efficiency?

This topic is relevent to energy efficiency because when you are re-designing a facility for new lighting, you may be able to reduce the wattage of your fixtures even further.  You should demand the lowest wattage fixture as possible.  If you understand the relationship between Scotopic and Photopic, you may be able to reduce your energy costs even further. 

Learn More About Energy Efficiency

Scotopic and Photopic vision are just 2 aspects of energy efficient technologies you must take into consideration.  To help you understand energy efficiency even further, download our FREE e-book, "Business Owners Guide To Energy Efficiency - Lighting Solutions".  You can click on the link here or the button below to get your copy.

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Topics: scotopic, photopic vision, cri color rendering index, color temperature, kelvin color temperature