Visible Light
And Its Surrounding Frequency Spectrums
The Light Spectrum
What we call "light" is actually several small packets of energy called "photons." A photon can carry different amounts of energy, which causes the photon to vibrate at a certain frequency. These photon frequencies range from billions of oscillation per second to less than one per second. This complete range of possible frequencies is known as the "electromagnetic spectrum."
How The Human Eye "Sees" Light
Light enters the eye through a special lens in the cornea, which focuses the light onto a special area in the back of the eye called the retina. The surface of the retina contains a dense field of special cells that change shape when exposed to photons within a certain range of frequencies. This change in shape is translated into visual information by the optic nerve and sent to the portions of the brain which controls sight.
However, the retina's cells are only sensitive to a narrow range of photon frequencies. This range is known as the "visible light spectrum."
How A Sony NightShot Camcorder "Sees" Light
Light enters the lens of the camcorder and is focused onto the surface of a silicon-based chip known as a "Charge-Coupled Device (CCD)." A CCD consists of hundreds of microscopic sensors called "capacitors" underneath a layer of light-sensitive silicon. When photons within a certain frequency range strike the silicon, it excites the latter's electrons in such a way that a very small electrical charge is produced. In turn, the capacitors trap and store all these charges.
Next, a small computer reads each capacitor's stored charges, translates the charges into light intensity and uses this information to construct a two-dimensional map of the image projected onto the CCD. This image is then reproduced in the viewfinder screen for the human eye to see.
How Can Sony NightShot "See" In The Dark
The silicon atoms in a CCD sensor react to photons within the "visible light" frequency range as well as frequencies above and below it. The frequency range just below the visible light spectrum is called "infrared." However, because the CCD will translate infrared light into unwanted visible light in the viewfinder, most camcorders include a special filter that blocks infrared light for filming in normal conditions.
To activate Sony NightShot, first flip a switch close to the lens. This pushes the infrared filter out of the way and turns on six special LED bulbs situated around the lens. These LED are designed to emit bright infrared light onto the area directly in front of the camcorder.
In darkness or very-low light situations, the infrared LEDs will be the only source of photons. When these photons hit the target, they reflect back toward the camera and hit the special silicon covering the CCD. The CCD's micro-capacitors then store the photoelectric charge, and the computer translates this data into a visible image map in the viewfinder.
Tags: visible light, frequency range, infrared light, photons within, certain frequency, change shape