A PowerPoint Presentation by Silescent Lighting Corporation on LED Lighting and the Science behind how people see.

1. 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?

2. THE PHYSIOLOGY OF SIGHT
How we see..

3. 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.

4. THE HUMAN EYE
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5. 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.

6. PHOTOPIC AND SCOTOPIC VISION
The 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.

7. 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.

8. 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.

9. 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.

10. THE SOLAR SPECTRUM
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11. COLOR TEMPERATURES
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12. VISIBLE SPECTRUM OF SUNLIGHT

13. 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.

14. LIGHT SPECTRA OF LAMPS
 Incandescent , fluorescent, LED and HID

15. WHITE LED SPECTRUM
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