Switching wavelength is particularly useful when the angle is small. Many polarimeters are equipped with a mercury lamp (in addition to the sodium lamp) for this purpose.
|
|
Gilles Holst (left), P. Teding van Berkhout and Balthasar van der Pol in 1925 Gilles Holst (20 March 1886 – 11 October 1968)Biography Portal of the Netherlands was a Dutch physicist, known worldwide for his invention in 1932 of the low-pressure sodium lamp.
|
|
In the past the light source would have been provided by a helium lamp or tube, but nowadays a more common source of monochromatic light is the low pressure sodium lamp. For a more thorough description of the physics behind this measurement technique, see interference.
|
|
238-241 J. J. de Groot, J. A. J. M. van Vliet, The High-Pressure Sodium Lamp,Macmillan International Higher Education, 1986, pp.13-17 Single- crystal artificial sapphire tubes were also manufactured and used for HPS lamps in the early 1970s, with a slight improvement in efficacy, but production costs were higher than for polycrystalline alumina tubes.
|
|
Diagram of a high- pressure sodium lamp. An amalgam of metallic sodium and mercury lies at the coolest part of the lamp and provides the sodium and mercury vapor that is needed to draw an arc. The temperature of the amalgam is determined to a great extent by lamp power. The higher the lamp power, the higher will be the amalgam temperature.
|
|
A so-called "yellow screen" is accomplished with a white backdrop. Ordinary stage lighting is used in combination with a bright yellow sodium lamp. The sodium light falls almost entirely in a narrow frequency band, which can then be separated from the other light using a prism, and projected onto a separate but synchronized film carrier within the camera. This second film is high-contrast black and white, and is processed to produce the matte.
|
|
Samples of ultracold atoms are typically prepared through the interactions of a dilute gas with a laser field. Evidence for radiation pressure, force due to light on atoms, was demonstrated independently by Lebedev, and Nichols and Hull in 1901. In 1933, Otto Frisch demonstrated the deflection of individual sodium particles by light generated from a sodium lamp. The invention of the laser spurred the development of additional techniques to manipulate atoms with light.
|
|
An unlit 35 W LPS/SOX lamp Warm-up phases of a LPS lamp. The faint pink light of the Penning mixture is gradually replaced by the bright monochromatic orange light of the metallic sodium vapor. A running 35 W LPS/SOX lamp Spectrum of a low-pressure sodium lamp. The intense yellow band is the atomic sodium D-line emission, comprising about 90% of the visible light emission for this lamp type.
|
|
The ceramic metal halide is a variation of the metal-halide lamp which is itself a variation of the old (high-pressure) mercury-vapor lamp. A CMH uses ceramic instead of the quartz of a traditional metal halide lamp. Ceramic arc tubes allow higher arc tube temperatures, which some manufacturers claim results in better efficacy, color rendering, and color stability. The discharge is contained in a ceramic tube, usually made of sintered alumina, similar to that used in the high pressure sodium lamp.
|
|
For example, sodium lamp street lighting has poor colour rendering capability as it's difficult to distinguish a red car from a yellow car. Current white light LED technology utilises a cerium doped YAG:Ce (yttrium aluminium garnet) down-conversion phosphor pumped by a blue (450 nm) LED chip. The combination of blue light from the LED and a broad yellow emission from the YAG phosphor results in white light. Unfortunately, this white light often appears somewhat blue and is often described as "cold" or "cool" white.
|
|
High-pressure lamps have a discharge that takes place in gas under slightly less to greater than atmospheric pressure. For example, a high pressure sodium lamp has an arc tube under 100 to 200 torr pressure, about 14% to 28% of atmospheric pressure; some automotive HID headlamps have up to 50 bar or fifty times atmospheric pressure. Metal halide lamps produce almost white light, and attain 100 lumen per watt light output. Applications include indoor lighting of high buildings, parking lots, shops, sport terrains.
|
|
Argon filled lamps are typically quite slow to start up, taking several minutes to reach full light intensity; xenon fill, as used in automotive headlamps, start up relatively faster. The ends of the arc tube are often externally coated with white infrared–reflective zirconium silicate or zirconium oxide to reflect heat back onto the electrodes to keep them hot and thermionically emitting. Some bulbs have a phosphor coating on the inner side of the outer bulb to improve the spectrum and diffuse the light. In the mid-1980s a new type of metal-halide lamp was developed, which, instead of a quartz (fused silica) arc tube as used in mercury vapor lamps and previous metal-halide lamp designs, use a sintered alumina arc tube similar to those used in the high pressure sodium lamp.
|
|