means the light that is already present in a scene, before any additional lighting is added. It usually refers to natural light, either outdoors or coming through windows etc. It can also mean artificial lights such as normal room lights.
Ambient light can be the photographer's friend and/or enemy. Clearly ambient light is important in photography and video work, as most shots rely largely or wholly on ambient lighting.
Unfortunately ambient light can be a real nuisance if it conflicts with what the photographer wants to achieve. For example, ambient light may be the wrong color temperature, intensity or direction for the desired effect. In this case the photographer may choose to block out the ambient light completely and replace it with artificial light. Of course this isn't always practical and sometime compromises must be made.
On the other hand, many of history's greatest photographs and film shots have relied on interesting ambient light. Unusual lighting can turn an otherwise ordinary shot into something very powerful.
Incident Light
Light seen directly from a light source (lamp, sun, etc)
Reflected Light
Light seen after having bounced off a surface.
Colour Temperature
Colour temperature is a standard method of describing colours for use in a range of situations and with different equipment. Colour temperatures are normally expressed in units called kelvins (K). Note that the term degrees kelvin is often used but is not technically correct (see below).
Technically speaking
Colour temperature means the temperature of an ideal black body radiator at which the colour of the light source and the black body are identical. (A black body is a theoretical radiator and absorber of energy at all electromagnetic wavelengths.)
Colour Temperature in Video
For video operations the relevant temperatures range from around 2,000K to 8,000K — these are common lighting conditions. In practical terms this usually means selecting lights, gels and filters which are most appropriate to the prevailing light or to create a particular colour effect. For example, a camera operator will select a "5600K filter" to use outside in the middle of a sunny day.
Terminology
When referring to the unit kelvin, it is not capitalised unless it is the first word of a sentence. The plural is kelvins (e.g. "The light source is approximately 3200 kelvins").
The symbol is a capital K (e.g. "The light source is approximately 3200K").
When referring to the Kelvin scale, it is capitalised (e.g. "The Kelvin scale is named after William Thomson (1824 – 1907), also known as Lord Kelvin".Contrast Ratio
Contrast Ratio is a measurement of the difference in brightness between the whitest white and the darkest black within an image. A ratio of 300:1 means the brightest point in the image is 300 times as bright as the darkest point. A higher contrast ratio therefore means a larger difference in brightness.
Contrast ratio is of interest in two situations:
Cameras: When recording an image (video, film, photography)
TVs, Monitors, etc. When choosing or setting up a playback device (TV, computer monitor, etc)
Key Light
The Standard 3-Point Lighting Technique
The Three Point Lighting Technique is a standard method used in visual media such as video, film, still photography and computer-generated imagery. It is a simple but versatile system which forms the basis of most lighting. Once you understand three point lighting you are well on the way to understanding all lighting.
The technique uses three lights called the key light, fill light and back light. Naturally you will need three lights to utilise the technique fully, but the principles are still important even if you only use one or two lights. As a rule:
If you only have one light, it becomes the key.
If you have 2 lights, one is the key and the other is either the fill or the backlight.
Key Light
This is the main light. It is usually the strongest and has the most influence on the look of the scene. It is placed to one side of the camera/subject so that this side is well lit and the other side has some shadow.
Fill Light
This is the secondary light and is placed on the opposite side of the key light. It is used to fill the shadows created by the key. The fill will usually be softer and less bright than the key. To acheive this, you could move the light further away or use some spun. You might also want to set the fill light to more of a flood than the key.
Back Light
The back light is placed behind the subject and lights it from the rear. Rather than providing direct lighting (like the key and fill), its purpose is to provide definition and subtle highlights around the subject's outlines. This helps separate the subject from the background and provide a three-dimensional look.
Hard Light
Light directly from a source such as the sun, traveling undisturbed onto the subject being lit.
Soft Light
Light which appears to "wrap around" the subject to some degree. Produces less shadows or softer shadows.
Spot
A controlled, narrowly-focused beam of light.
Flood
A broad beam of light, less directional and intense than a spot.
Tungsten
Light from an ordinary light bulb containing a thin coiled tungsten wire that becomes incandescent (emits light) when an electric current is passed along it. Tungsten colour temperature is around 2800K to 3400K. Also known as incandescent light.
Halogen
Type of lamp in which a tungsten filament is sealed in a clear capsule filled with a halogen gas.
Fresnel
A light which has a lens with raised circular ridges on its outer surface. The fresnel lens is used to focus the light beam.
Incandescent
Incandescent lamps produce heat by heating a wire filament until it glows. The glow is caused by the filament's resistance to the current and is called incandescence.
There are many different units for measuring light and it can get very complicated. Here are a few common measurement terms:
Candela (cd)
Unit of luminous intensity of a light source in a specific direction. Also called candle.
Technically, the radiation intensity in a perpendicular direction of a surface of 1/600000 square metre of a black body at the temperature of solidification platinum under a pressure of 101,325 newtons per square metre.
Footcandle (fc or ftc)
Unit of light intensity, measured in lumens per square foot. The brightness of one candle at a distance of one foot. Approximately 10.7639 lux.
Lumen (lm)
Unit of light flow or luminous flux. The output of artificial lights can be measured in lumens.
Lux (lx)
Unit of illumination equal to one lumen per square metre. The metric equivalent of foot-candles (one lux equals 0.0929 footcandles). Also called metre-candle.
There are many different units for measuring light and it can get very complicated. Here are a few common measurement terms:
Candela (cd)
Unit of luminous intensity of a light source in a specific direction. Also called candle.
Technically, the radiation intensity in a perpendicular direction of a surface of 1/600000 square metre of a black body at the temperature of solidification platinum under a pressure of 101,325 newtons per square metre.
Footcandle (fc or ftc)
Unit of light intensity, measured in lumens per square foot. The brightness of one candle at a distance of one foot. Approximately 10.7639 lux.
Lumen (lm)
Unit of light flow or luminous flux. The output of artificial lights can be measured in lumens.
Lux (lx)
Unit of illumination equal to one lumen per square metre. The metric equivalent of foot-candles (one lux equals 0.0929 footcandles). Also called metre-candle.
