White Reflector Research Articles

New investigations concerning the relationships between congenital colour vision defects and road traffic security

New extentive experiments demonstrated that: (a) protan observers are more deficient than deutan ones with regard to perception distances of some traffic panels, of vehicle red stop lights, of vehicle red rear-position lights and of white, yellow and red reflectors. Contrarily, deutan observers are more deficient than protan ones for the distinction of differently coloured traffic lights and vehicle rear lights; (b) protan and deutan drivers are nevertheless not responsible for more traffic accidents than drivers with normal colour vision; (c) this apparent contradiction is due to psychological compensation mechanisms. The practical conclusions are: (a) that persons with defective colour vision need not to be excluded from non professional road traffic; (b) that it is nevertheless useful that they should be aware of their handicap; (c) that the red traffic signal has to be larger than the other ones; and (d) that the stop and red position lights of vehicles must be sufficiently intense and that the filters transmitting only pure red should be avoided in them.

Studies on the eyes of catfishes with special reference to the tapetum lucidum.

Marine catfishes (Ariidae) and freshwater catfishes (Ictaluridae) have ocular tapeta lucida. Species examined wereBagre marinus(Mitchill),Arius felis(L.),Ictalurus punctatus(Rafinesque),I. natalis(Lesueur),I. nebulosus(Lesueur) andPylodictis olivaris(Rafinesque). The tapeta are white reflectors located in the pigment epithelium; they occupy most of the fundus except for a narrow black ventral field. A more extensive study was made of the tapetum of the hardhead catfishA. felis. In histologic sections the tapetum is yellow brown and is easily confused with retinal pigment. It can be distinguished because it stains with ferric-ferricyanide and dissolves in methanol-hydrochloric acid after Carnoy fixation. The tapetum is occluded by melanosomes which move inwards in light, and it is exposed by movement outwards of melanosomes in dim light or darkness. Electron microscopy shows that processes of the pigment epithelial cells contain many membrane-bound tapetal spheres which enclose the tapetal pigment and are responsible for reflexion of light. Spheres are 370 nm in diameter (average); there are about 5.5 spheres in 1 μm3, and the tapetum is about 90 μm thick. Rods and cones are equal in number; rods form a single layer, cones are single and possess an accessory outer segment. Transmission of the tapetum is minimal at short wavelengths and rises steadily above 500 nm. Reflectance is diffuse; it rises to a maximum at 500 nm, and is high at long wavelengths. The tapetum has a high refractive index,ca. 1.56, favouring light scattering. Some characteristics of the extracted tapetal pigment are pre­sented: it is light yellow, and absorbance maxima occur at 260 and 330 nm in acidic meth­anol. The pigment epithelium contains lysosome-like bodies but no myeloid bodies. The hardhead retina contains a visual pigment 5272. Measurements of natural light (irradiance) in coastal waters inhabited by sea catfishes are presented: the waters are turbid and transmit maximally at 575 to 580 nm. The findings, in relation to earlier work on the catfish eye, performance of the eye and habits of the fish are discussed.

Tapeta lucida in the eyes of the seatrout (Sciaenidae)

Eyes of the seatrout (Sciaenidae) contain a tapetum lucidum, located in processes of the pigment epithelial cells. The tapetum is a white diffuse reflector, occluded by black retinal pigment by day, and exposed by retreat of pigment at night; threshold for pigment migration is around 10 lx. Reflexion is caused by backscattering of light from a multitude of small spheres, each about 0.4μm in diameter, packing the cell processes. Material has been examined by electron microscopy, employing epoxide sections and freeze-etch techniques. The spheres have homogeneous, densely staining contents and are surrounded by thin boundary membranes. The reflecting material is a lipid, it has been extracted, purified by column and thin-layer chromatography, and characterized by TLC and GLC. On TLC it runs at the same rate as triglycerides, and is demarcated according to class from wax esters, sterols and diacyl glyceryl ethers. It contains predominantly one fatty acid,n— C22 : 6 ( ≥ 95%), and appears to be largely tridocosahexaenoin. The tapetum contains 1.5 mg of triglyceride per square cm. The relationship of the tapetum to the photoreceptors and some characteristics of the latter are described, and reference is made to the occurrence of similar lipid tapeta in other families of fishes.

Small-signal gain of a CO2laser amplifier utilizing a white optical reflector design

A small-signal gain of 39 dB in a nonresonant multi-path CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> laser amplifier with a discharge length of 65 cm is reported. The multipath system employed is a modified White optical reflector design. An unsaturated gain of 39 dB was observed for signals smaller than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> watt. No noise component, due to the amplifier, was detected for signals as small as <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5 \times 10^{-8}</tex> watt.

Effect of optical systems and sample preparation on the visible reflection spectra of pork muscle

AbstractThe technique for measuring the reflectance spectrum over the visible range of pork muscle, as influenced by optical design and sample preparation, was examined.Of the three optical systems used to measure light reflectance from muscle, the best resolution of the spectra was achieved with integration spheres.The influence on the reflection spectra of the following factors was investigated: muscle surface, transparent film, depth of sample, longitudinal and transverse sections of muscle fibres, and the effect of fat. The spectra of samples within the longissimus dorsi muscle was affected by pH, but not by vertebral location.A thin sample covered with a glass cover slip and with a white rear reflector produced the maximum resolution of muscle pigments.

Further aspects of the artificial illumination of plant growth chambers

Tubular low-pressure mercury fluorescent lamps with and without an internal reflector are compared. When an efficient external white reflector is provided and the lamp environment is dust-free, plain lamps give 10% greater light intensity than reflectorized lamps. Using a double-tier lighting unit, individual switching of lamps is shown to offer a wide range of intensities between 3500 and 400 lm/ft 2. Dimming of only six lamps extends the range down to 10 lm/ft 2. Reasonable horizontal uniformity of illumination in a horizontal plane is retained in all cases. An electrical circuit is described for use with photo-periodic work in which selected lamps in a lighting unit can be used as a night-break or for an extended day. The range of night-break duration is from 5 s to several hours using standard commercial time-switches. A design of fitting for incandescent lamps is described which is physically interchangeable with a tubular fluorescent lamp. Recommended lamp spacing and the resultant intensity distribution in a horizontal plane is given. Using a lighting unit containing tungsten filament and fluorescent lamps, the relative contributions to intensities are given in both energy and photometric units. Values of total radiation are used in conjunction with spectral curves of the lamps to predict the “red” to “far-red” ratio. The significance of the artificial sky type of illumination is discussed. Using a 27-in cube, various light-reflecting materials are compared. Self-adhesive metallized Melinex is recommended for lining the walls of growth chambers when both the lamp bank and the plant plot extend right up to the walls; white paint, aluminium sheet and stainless steel sheet are shown to be unsuitable.

Ocular Fatigue

Publications by ophthalmologists in regard to safety for motorists have dealt principally with visual requirements of drivers. Ocular fatigue should also be considered as a contributing factor in automobile accidents, and means of decreasing it should be of interest to the ophthalmologist as a motorist. Automobile accidents account for over a million injuries and more than 38,000 deaths each year in the United States. No data have been found listing the eyes damaged or lost in highway accidents. However, it can be safely assumed that many eyes of the million injured have been ruined. This should be of concern to ophthalmologists. It apparently has not been appreciated how tiring and disturbing the rapidly repeated visual stimuli caused by long stretches of white guard posts, reflectors, and broken white lines on the road's surface can be, particularly at night. They also have a hypnotic effect on some drivers. Statistics published by

STUDIES ON THE REDUCTION OF A TETRAZOLIUM SALT BY GREEN PLANT TISSUE

ALL PREPARATIONS of grana or chloroplasts isolated from green plants and still capable of performing the photochemical reductions known as the Hill reaction suffer to an unknown degree from structural deformations and from contaminations with cytoplasmic material. From the standpoint of correlating chloroplast structure and function, it would be of considerable help if fractionation experiments could be supplemented by a cytochemical method to localize the Hill reaction in individual chloroplasts of intact cells. Tetrazolium salts are compounds which have been valuable in localizing enzymatic reductions in many plant and animal cells because their colorless, water-soluble form is reduced to a colored, insoluble pigment at the site of activity; the literature on salts has been reviewed recently by Smith (1951). A method has been devised in which a salt is photochemically reduced and may possibly serve as an indicator of the Hill reaction. Results of preliminary experiments using the method are reported in this paper. MATERIALS AND METHODS.-The salt used in these experiments was blue tetrazolium (BT), a new ditetrazolium salt described by Rutenburg et al. (1950) and supplied by the Dajac Laboratories. This compound turns reddish purple when partially reduced and yields a stable, insoluble, blue-black diformazan when completely reduced. 2, 3, 5-triphenyltetrazolium chloride was tried and was found to be unsuitable for these experiments because the solution is unstable when exposed to light. The test solution ordinarily contained 1 part BT stock solution (1 mg./ml.), 1 part M/10 phosphate buffer, pH 6, and 2 parts water. In some experiments solutions of organic acids or sugars were substituted for part of the water. Phosphate buffer with a pH of 7.5 was used for blue-green algae. The solution used for marine algae contained 1 part BT solution and 3 parts sea water. With most of the plant materials the reaction was only slight when the experiments were conducted in air but was satisfactory when the material was under nitrogen, under hydrogen, or in evacuated tubes. For most of the experiments the solutions and plant material were placed in Thunberg tubes and evacuated 3 min. with a vacuum pump giving a pressure less than 1 cm. Hg. The tubes were placed immediately either into a water bath in a dark, 33?C. incubator or into an illuminated water bath kept at approximately 33?C. by running tap water. The water bath was a glass vessel illuminated from below by a 100 w. tungsten bulb in a white reflector;