Illumination sources

Impairment of visibility involves degradation of the ability to perceive the environment. Several factors are involved in determining visibility in the atmosphere (Fig. 10-1) the optical characteristics of the illumination source, the viewed targets, the intervening atmosphere, and the characteristics of the observer s eyesight (1). 

Incandescent lamps consist of glass bulbs that enclose an electrically heated filament that emits light. For over 50 years prior to Thomas Edison s success, scientists had experimented with developing electric lamps. With financiers such as J. P. Morgan and the Vanderbilts, Edison founded the Edison Electric Light Company in 1878 with the prime mission to generate cheap electric power to provide an illumination source. For the filament of his electric lamp, Edison reportedly experimented on 6000 different types of materials, eventually narrowing his focus on fine platinum wire and a mix of 10% iridium with platinum. Unfortunately,... 

The proper implementation of the CIE system requires use of a standard illumination source for calculation of the tristimulus values. Three standard sources were recommended in the 1931 CIE system, and these may be presented in terms of color temperatures (the temperature at which the color of a black-body radiator matches that of the illuminant). The, simplest source is an incandescent lamp, operating at a color temperature of 2856 K. The other two sources are combinations of lamps and solution filters designed to provide the equivalent of sunlight at noon, or the daylight associated with an overcast sky. The latter two sources are equivalent to color temperatures of 5000 K and 6800 K, respectively. 

The actual determination of color is made with a photoelectric tristimulus colorimeter fitted with a CIE illuminating source. Measurements are made relative to a standard (usually magnesium oxide or barium sulfate) taken through... 

The properties of different illumination sources that can be combined with the set-ups discussed above are presented in Section 4.6. 

Cell/substrate contacts can be located by a nonfluorescence technique completely distinct from TIRF, known as internal reflection microscopy (IRM).(1 9) Using conventional illumination sources, IRM visualizes cell/substrate contacts as dark regions. IRM has the advantage that it does not require the cells to be labeled, but the disadvantages that it contains no information about biochemical specificities in the contact regions and that it is less sensitive to changes in contact distance (relative to TIRF) within the critical first lOOnm from the surface. 

G. Bock, M. Hilchenbach, K. Schaenstein, and G. Wick, Photometric analysis of antifading reagents for immunofluorescence with laser and conventional illumination sources,... 

Figure 8.1 Schematic representation of NIR chemical imaging instrument operating in diffuse reflectance mode. Radiation from the illumination source interacts with the sample. Light reflected off of the sample is focused onto a NIR sensitive 2D detector after passing through a solid-state tunable wavelength selection filter.

When transparent glasses absorb portions of the visible spectrum from 400 to 700nm, they will appear colored. The color is determined by the transmitted portion of the visible spectrum after subtracting certain wavelengths by absorption from the illuminating source. 

Caution must be exercised around the illuminating source as it may be hot. Avoid looking directly at the illuminating source. 

A 2h inch diameter by 1/8" thick quartz plate was attached to the bottom of the cell, forming a UV window. A pen-ray quartz UV lamp and power supply were employed for the illumination source. The lamp was housed in a minibox fixed with a shutter (ILEX No. 3 Universal). 

Microscopes used in LM are composed of a beam of visible light (photons) that represents the illumination source (probe), a system for focusing the source onto the sample (the condenser or condense glass lens), a location to place the sample or specimen, and the objective. 

Wet samples can be analyzed without a previous preparation by the so-called environmental scanning electron microscopy (ESEM). In this technique, instead of the vacuum conditions, the sample chamber is kept in a modest gas pressure (Bache and Donald, 1998). The upper part of the column (illumination source) is kept in high vacuum conditions. A system of differential pumps allows to create a pressure gradient through the column (Bache and Donald, 1998 Stokes and Donald, 2000). The choice of the gas depends on the kind of food hydrated food is kept under water vapor. 

As the reflected radiation is emitted from the sample in a random direction, diffusely reflected radiation can be separated from, potentially sensor-blinding, specular reflections. Common techniques are off-angle positioning of the sensor with respect to the position(s) of the illumination source(s) and the use of polarisation filters. Application restrictions apply to optically clear samples with little to no scattering centres, thin samples on an absorbing background and dark samples. In either of these cases, the intensity of radiation diffusely reflected off such samples is frequently insufficient for spectral analysis. While dark objectives remain a problem, thin and/or transparent samples can be measured in transmission or in transflectance. 

In 1986, Foret et al.41 described an on-line UV absorbance detector that employed a commercial photometer and optical fibers in direct contact with the outer walls of the separation capillary. The optical fibers (200 (im I.D. fused silica core) conducted the light beam perpendicularly across the migrating zones one fiber was connected to a mercury lamp to serve as the illumination source, and the other directed light to a photomultiplier tube for detection. The detector was found to be linear in the range of 10"5 to 10 3 M (r = 0.994 for 10 measurements), with detection limits of 1 X 10 5 M for picric acid (S/N = 2). 

The illumination source was a xenon illuminator (Cermax, ILC Technology, Sunnyvale, Cal.) operated at 180-320 W and situated 34-38 cm from the photolysis cell. The spectrum of the output of this lamp closely simulated the solar spectrum over the 300-700 nm wavelength region. To avoid thermal decomposition of samples undergoing illumination, the near-infrared component of the lamp output was attenuated by inserting a 20-cm water filter between the lamp and a sample. A portion of each sample of adsorbed PAH was stored in the dark, as a control, to ensure that no detectable non-photochemical decomposition of the PAH occurred during the duration of illumination. 

In remote-sensed reflectance spectra of planetary surfaces measured through Earth-based telescopes, the Sun is the illuminating source. Light reaching... 

Many fluorescent dyes and proteins now available enable multiple detection channels and the ability to multiplex related assays. HCS assays typically use at least two channels one for a DNA stain and another for the fluorophore of interest. In general, the maximum number of channels utilized at one time ranges from two to five. Instrument hardware and driver software determine the number of channels and fluorophores to be acquired. Some factors to consider here include illumination source (arc lamp or laser), filter and mirror requirements, number of cameras or PMT detectors, camera sensitivity, and desired detection wavelength range. Other considerations for multiplexing include read time, resolution, and assay time (for live cell imaging). 

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