TALKING POINTS What is energy? What is light? What is work? What is heat? What is power? (kw/hr) What is electroluminescence? (LED) How do we see? What is scotopic and photopic vision? How do Silescent fixtures work?

THE PHYSIOLOGY OF SIGHTHow we see..

THE ELECTROMAGNETIC (LIGHT) SPECTRUM Visible light has a wavelength in a range from about 380 or 400nanometres to about 760 or 780 nm, with

a frequency range of about 405 THz to 790 THz. The total range of light wavelengths we can measure spans an incredible range of almost 20 powers of ten from the shortest gamma rays to the longest radio wavelengths. 

THE HUMAN EYE

CONE SPECTRAL RESPONSE - COLOR The cones in the eye respond to red, green, and blue in overlapping response  The "green"

and "red" cones are mostly packed into the fovea centralis. By population, about 64% of the cones are red-sensitive, about 32% green sensitive, and about 2% are blue sensitive. The "blue" cones have the highest sensitivity and are mostly found outside the fovea. The shapes of the curves are obtained by measurement of the absorption by the cones, but the relative heights for the three types are set equal for lack of detailed data. There are fewer blue cones, but the blue sensitivity is comparable to the others, so there must be some boosting mechanism. In the final visual perception, the three types seem to be comparable, but the detailed process of achieving this is not known.

PHOTOPIC AND SCOTOPIC VISIONThe two curves show the normalized sensitivity of the cones (black/photopic) and rods (green/scotopic) to the visible light spectrum. In bright light found outdoors photopic sensors dominate vision. In dim light scotopic vision dominates. In medium light levels produced by artificial light sources inside buildings, both photopic and scotopic sensors are used to see. This is called mesoptic vision.

mesoptic vision [me′zäp·tik ′vizh·ən] Vision in which the human eye's spectral sensitivity is changing from the photoptic state to the scotoptic state.

RODS AND CONES Rods: See in black, white, and shades of gray and tell

us the form or shape that something has. They are super-sensitive, allowing us to see when it's very dark.

Cones: Sense color and need more light than Rods to work well. Cones are most helpful in normal or bright light. There are 3 types of cones - red, green, and blue - to help you see different ranges of color. Together, these Cones sense combinations of light waves that enable our eyes to see millions of colors. The retina in the fovea has 200,000 of these photoreceptors for every square millimeter.

ADAPTATION Dark Adaptation: When we move from a lit room to a dark

room, we cannot see clearly, because not enough stimulated rhodopsin (peripheral): rhodopsin is bleached faster than it is reformed in strong light, insufficient rhodopsin reformed instantaneouslycones are not stimulated: light intensity too low. It takes about 20 minutes for enough rhodopsin to reform for us to see properly.

Light Adaptation: When we move from a dark room to a brightly lit room, we feel uncomfortable from the glare. But after some time, the visual threshold in Cones (foveal) increases relative to the generator potential. Cones is less stimulated, and we will see better. This takes about 5 minutes.

GAIN OF THE EYE  The human rods have a dynamic range of about 10

billion-to-one. In other words, when fine-tuned for high gain amplification (as when you are out on a dark night and there is only starlight), your photoreceptors can pick up a single photon. Phenomenal sensitivity! Of course the retina does a number of processing tricks on that just to make sure it is not picking up noise, so you don't see static; it really wants at least six receptors in the same area to pick up the same signal before it "believes" that it is true and sends it to the brain. In bright daylight the retina bleaches out and the volume control turns way down for, again, admirable performance.

THE SOLAR SPECTRUM

COLOR TEMPERATURES

VISIBLE SPECTRUM OF SUNLIGHT

CIRCADIAN RYTHYM AND BLUE LIGHT Circadian rhythm In humans, melatonin is produced by the pineal gland, a gland about the size of a pea, located in

the center of the brain but outside the blood-brain barrier. The melatonin signal forms part of the system that regulates the sleep-wake cycle by chemically causing drowsiness and lowering the body temperature, along with the central nervous system: the paracrine and endocrine systems

Light dependence Production of melatonin by the pineal gland is inhibited by light and permitted by darkness. For

this reason melatonin has been called "the hormone of darkness". Its onset each evening is called the Dim-Light Melatonin Onset (DLMO). Secretion of melatonin as well as its level in the blood, peaks in the middle of the night, and gradually falls during the second half of the night.]

It is principally blue light, around 460 to 480nm, that suppresses melatonin,[35] increasingly with increased light intensity and length of exposure. Until recent history, humans in temperate climates were exposed to few hours of (blue) daylight in the winter; their fires gave predominantly yellow light. Wearing glasses that block blue light in the hours before bedtime may avoid melatonin loss. Kayumov et al. showed that light containing only wavelengths greater than 530 nm does not suppress melatonin in bright-light conditions. Use of blue-blocking goggles the last hours before bedtime has also been advised for people who need to adjust to an earlier bedtime, as melatonin promotes sleepiness.

LIGHT SPECTRA OF LAMPS Incandescent , fluorescent, LED and HID

WHITE LED SPECTRUM