Lamp Output Research Articles

Transient arc self-inductance and simmer effects in linear flashlamps for laser pumping

The physical processes influencing lamp stability and efficiency are studied in this paper. Experimental evidence demonstrates that undesirable lamp output energy variation is believed to be caused by the random nature of the triggering process. The random effect can be decreased by the induced back emf of the transient arc self-inductance under the preferred trigger polarity and the simmer mode operation of the lamp. Simmering a lamp results in a uniform current and plasma density, hence higher optical efficiency is obtained. The best simmer action is provided by the full simmer mode; it allows the arc to grow uniformly from the axis of the lamp.

Irradiance and plant temperature monitor/controller

An irradiance and plant temperature monitor/controller has been developed and is being tested for use in controlled environments and in commercial greenhouses. Photosynthetic photon flux density was monitored using a quantum sensor, while plant temperature was monitored with an infrared thermometer. A microprocessor integrated the signals from each sensor and permitted a choice of priority control of high-intensity discharge (HID) lamps or infrared (IR) heaters for control of plant temperature. It also permits dimming of HID lamps inversely proportional to natural irradiance. Effects of the monitor/controller changes on high-pressure sodium lamp output to input ratio, lamp life and dimming response time will be illustrated. The effects of irradiance variations on leaf heating and cooling are presented.

Increased efficiency of emission of hollow-cathode lamps fed by short current pulses monopulse correction

Many problems in applied spectroscopy, for example the study of the space-time characteristics of the flame of the discharge in resonance detectors, determination of the concentration of chemical elements by absorption spectroscopy in laser or arc atomization, and increased speed of absorption spectrometers operating with electronic modulation of radiation sources and nonflame atomizers, require lamps with a hollow cathode with current pulse duration of the order of 10-50 /sigma phi/ sec. The limitation of the light output of hollow-cathode lamps in these cases significantly worsens the final results of the studies due to the low signal-to-noise ratio and higher fluctuations of the light emission caused by unavoidable transient processes in the development of glow discharge. The authors study the development of the light pulse of hollow-cathode lamps excited by rectangular current pulses. This article includes a table of the dependence of the instability emission of copper, tungsten and vanadium in an LT-2 lamp on the duration of the additional current pulse /tau//sub 2/ with I/sub 1/=100mA and with duty factor of Q=10.

Optical output stabilization method for direct current arc lamps

A simple, effective technique for stabilizing the optical output of direct current (dc) arc lamps is described. The large output fluctuation due to arc wander in a commercially available lamp and power supply is minimized by the introduction of an alternating current (ac) waveform superimposed on the dc source voltage in conjunction with detector averaging. Arc stability is monitored indirectly by the detection of arc excited fluorescence from a standard sample. The monitored lamp output is typically maintained to within 1% relative standard deviation (RSD) by this method. Data are presented supporting the theory that arc wander is significantly reduced by the addition of an ac component to the dc lamp power. Various methods of ac introduction are discussed along with the design of a controllable oscillator circuit. The effects of variations in ac voltage and frequency on optical output stability are examined.

Fading of quinoline dye by light: application to the measurement of the integrated lamp output and solar energy

The fading rates of plastic plates dyed with a quinoline derivative (quinophthalone) have been measured under exposure to light of 366-, 404.7-, and 435.8-nm wavelengths and to a high pressure Xe arc. The initial quantum yield of fading is 2 x 10(-5) and is independent of incident wavelengths. The correlation between the fading by lamp exposure and that by solar exposure is obtained using a filtered 1000-W Xe arc, a simulated solar radiation source. The fading plates provide simple and inexpensive means to measure the integrated lamp output and solar energy.

Optimization of Pulsing Conditions for Hollow Cathode Lamps for Atomic Fluorescence Spectrometry

The effect of pulsing conditions on hollow cathode lamp output, on the intensity of atomic fluorescence excited, and on atomic fluorescence detection limits has been examined for a number of commercial sealed lamps. Optimization must be carried out on an individual lamp basis. Maximum integrated intensity is obtained by minimizing the dc current through the lamp and making the duty factor as large as possible within the limit set by the maximum allowed average current through the lamp. Integrated intensity is largely independent of pulse width and depends only to a small extent on peak current. For the range of operating conditions considered in this study, the effect on atomic fluorescence of line broadening due to pulsing at high peak currents was small.

Evaluation of a pulsed EIMAC source for atomic-fluorescence spectrometry

An EIMAC xenon arc continuum source operated in the pulsed mode has been evaluated for potential use as a source of excitation in atomic-fluorescence spectrometry. The results were compared with those obtained with a similar lamp operated in the continuous-wave mode; little or no improvement was evident from this comparison. The lamp was found to be unstable in the pulsed mode, requiring the use of a rather large residual d.c. current in conjunction with a relatively low amplitude power-pulse in order to sustain the arc. Moreover, the pulsed source yielded a large background signal because of scattering of source-radiation in the flame; the background spectrum (`with source “on”) contained numerous large peaks due to fluorescence of molecular species in the flame and to irregularities in the spectral distribution of the pulsed lamp output transmitted to the signal detector by scatter.

Lamps for light-trapping

Upton's work suggests that this coating has decreased the long-wavelength ultraviolet output of high pressure mercury vapour lamps from 3 to 1% of the initial wattage, and has removed it almost completely in the case of blended lamps. This means that all coated lamps which do not require a choke have low performance in light traps, and choked lamps are not much better. (A choke is a device which provides high impedance in the otherwise low resistance circuit of a light trap. This prevents failure of the unit and decreases the amount of power used while the light is in operation). Along with changes in general purpose lamps has come the emergence of lamps designed for special purposes, such as for entertainment lighting and the study of watermarks. Some of these appear to offer good prospects for light trapping success.

Radiation Environment of Growth Chambers1

Abstract Radiation measurements with different types of meters in several controlled environment facilities have been compiled to demonstrate the problems associated with insuring uniform radiation levels in separate faciities. Data are provided for a quantum meter, three photometers, a pyranometer and a far-red energy meter. Significant variations in total radiant energy in chambers under similar photosynthetically active radiation (PAR) levels were demonstrated. Measurement of light under cool white fluorescent and incandescent lighting with calibrated photometers from different manufacturers, varied by 20%. Greater variation occurred when photometer measurements were compared under different types of lamps. One of the most significant variations in different chambers was the intensity of incandescent radiation. This could only be effectively monitored and controlled with the far-red sensor. Factors are given for conversion between quantum, photometric and radiometric measurements, but high precision cannot be assumed in the use of these factors because of the differences in instrument sensitivity and variations in spectral output of lamps. The study documents the need for calibration of instruments under the same type of light source that is utilized in the growth chambers and for the use of more than one type of sensing instrument to quantify the radiation that controls plant growth.

Aspects of scanning microdensitometry. III. The monochromator system.

Microdensitometric errors can result from various factors associated with the monochromator system, including imperfect monochromaticity of the light, incorrect setting of the wavelength, and non-uniform illumination of either the microscopic field or the objective aperture. Certain types of potential error are characteristic of particular instruments. Thus in the Vickers M85 microdensitometer, where the flying spot is the reduced image of a hole situated at the monochromator exit aperture, the interpretation of results obtained with different spot sizes is complicated by the fact that the hole size affects both the spatial resolution and the spectral bandwidth of the system. Similarly, in instruments in which the monochromator exit slit lies in an aperture plane the numerical aperture of the whole system may be affected by the spectral bandwidth and vice versa. Overall instrumental sensitivity is mainly limited at the blue and red ends of the spectrum respectively by the lamp output and the photomultiplier tube sensitivity. Quartz-iodine lamps are slightly brighter than conventional tungsten sources, especially at short wavelengths, but tend to be less stable photometrically and are more expensive. Simple refracting monochromators and graded-spectrum interference filters in general pass more light, in the visible spectrum, than do grating monochromators of similar bandwidth. Most errors of wavelength setting can be avoided by routinely measuring at that wavelength, lambda(max), found empirically to give the maximum absorbance or integrated absorbance. Off-peak wavelengths can be set reproducibly with the aid of an eyepiece spectroscope, or by adjusting the wavelength so that the absorbance of a given specimen is some precise fraction of that at lambda(max).

The Effects of Light Intensity and Spectral Quality on Growth and Shoot Initiation in Tobacco Callus

The effects of eight different narrow band-emitting fluorescent lamps (371-750 nm) and four commercial broad band-emitting fluorescent sources upon growth and shoot initiation in tobacco callus (Nicotiana tabacum var. Wisconsin 38) have been characterized. Wavelength and intensity are equally important parameters in determining morphogenic changes. Near ultraviolet light (371 nm) was found to stimulate (0.024 mw/cm(2)) or inhibit (above 0.15 mw/cm(2)) callus growth and shoot initiation, depending on the light intensity. Stimulation of growth and shoot production occurs also in blue light region, but at higher intensity than in the near ultraviolet. Red and far red light (up to 1.7 mw/cm(2)) do not appear to affect callus growth or stimulate shoot initiation. The enhancement of callus growth and the stimulation of shoot initiation are controlled by the same near ultraviolet-absorbing photoreceptor system present in a small enough concentration that it cannot be recognized in the absorption spectrum of the intact tissue. Carotenoids, porphyrins, and phytochrome associated with the high irradiance response do not appear to qualify as the photoreceptor. Flavonoids are possible candidates. Radiation emitted by fluorescent lamps outside the near visible region was determined, and we concluded that energy levels were not sufficient to affect the reported results. The spectral output of several commercial lamps in the visible and near visible regions is such that there could be different effects on growth and development of tissue cultures.

Flashlamp Discharge and Laser Efficiency

This paper presents an improvement in the method of calculating flashlamp performance and indicates how this can be used to evaluate the effect of flashlamp related system parameter changes on the efficiency of a solid state laser using such a flashlamp as a pump. It is shown that, in addition to being functions of the alpha and beta constants in the well-known theory of Markiewicz, Emmett, and Holzrichter, the normalized peak current and pulse width are also functions of the input energy. Furthermore, the product of peak current and pulse width is indicated to be the most significant factor relating lamp input and output. Finally, a curve is given for the fluorescence pumping efficiency and scaling of laser input-output levels is discussed.

Letter: Infants endangered by phototherapy.

To the Editor. —The appearance of erythema on the skin of two infants exposed to fluorescent lights as treatment for hyperbilirubinemia has come to the attention of the Food and Drug Administration. On-site investigation of the incident by personnel of the FDA Bureau of Radiological Health indicated that the clinical determination of erythema was consistent with the measured ultraviolet exposure levels. The occurrence indicates an urgent need to alert physicians and hospitals to the possibility of injury to the exposed infant from certain exposure conditions that may be used in phototherapy. Hazardous levels of ultraviolet radiation, which are not effective in phototherapy, and extremely intense visible radiations can be present in the output of fluorescent lamps. The agency strongly recommends that any institution, or physician, using phototherapy in the treatment of hyperbilirubinemia immediately take the following precautions: Shield fluorescent lamps with ultraviolet absorbing filter materials made from selected plastics or

Ultraviolet Light Hazards From Phototherapy

To the Editor.— The appearance of erythema on the skin of two infants exposed to fluorescent lights as treatment for hyperbilirubinemia has come to the attention of the Food and Drug Administration. On-site investigation of the incident by personnel of the FDA Bureau of Radiological Health indicated that the clinical determination of erythema was consistent with the measured ultraviolet exposure levels. The occurrence indicates an urgent need to alert physicians and hospitals to the possibility of injury to the exposed infant from certain exposure conditions that may be used in phototherapy. Hazardous levels of ultraviolet radiation (which are not effective in phototherapy) and extremely intense visible radiations can be present in the output of fluorescent lamps. The agency strongly recommends that any institution, or physician, using phototherapy in the treatment of hyperbilirubinemia immediately take the following precautions: Shield fluorescent lamps with ultraviolet-absorbing filter materials made from selected plastics or

Mercury Dispensing and Gettering in Fluorescent Lamps

A new method of introducing mercury, based on the thermal decomposition of a stable intermetallic compound of titanium and mercury, has been developed. This method is considerably simpler and more accurate than those previously employed and should permit a more rapid production of fluorescent lamps. Health problems are also greatly reduced as reduced quantities of mercury are used and these are released only after closure of the lamp. By association of a zirconium-aluminium non-evaporable getter alloy with the intermetallic compound, removal of gaseous impurities is achieved, which may aid starting the discharge, and improve luminous output and stability of fluorescent lamps.

Emission characteristics of 50-100 μsec pulse discharges in xenon

The conditions necessary for achieving the maximum output of ultraviolet pulse-discharge lamps, needed for the pumping of dye lasers, were determined by investigating 50–100 μsec pulse discharges in xenon. The dependences of the total and the ultraviolet emission efficiencies on the average specific discharge power were determined and explained. The spectral and the spectral-temporal characteristics of a xenon discharge in the λ = 220–650 nm range were determined under conditions which ensured the maximum value of the ultraviolet emission efficiency.

Chemical variables and new lamps in phototherapy.

Extract: In vitro studies were undertaken to measure the effects of varying concentrations of albumin and flux on the photodecomposition of bilirubin. By using an experimental model, the effect of albumin on photodegradation of bilirubin was determined. Synthetic crystalline bilirubin solutions (20 mg/100 ml, pH 7.4) were exposed to the same flux levels for periods of 4.5 hr. The only variable in this series was the concentration of albumin, ranging from 0.5 to 5 g/100 ml. As the the concentration of albumin increased, the reaction rate decreased (Fig. 5). The efficiency of phototherapy was studied by varying flux levels while maintaining other variables constant. Figure 6 shows a nonlinear relation between reaction rate and flux, in which higher flux levels resulted in less decomposition per amount of flux (i.e., efficiency). More than twice the flux level was required to attain a twofold increase in decomposition rate. The effect of light flux was such that continuous use of the lowest practical level is to be recommended. Data are given on the comparison of the relative effectiveness of cool white, high intensity blue, and two experimental lamps. The four lamps were tested at conditions of constant distance and constant flux. The high intensity blue lamp was twice as effective as the cool white. The two experimental lamps showed a 17% increase over the blue lamp (Figs. 2 and 3). The effect of time on the spectral output of the fluorescent lamps in an experimental model was determined by using a spectral radiometer. The energy dropoff within the 420− to 480-nm region at 200 hr was approximately 20% for blue lamps and averaged 7.5% for the experimental lamps. Speculation: As with any new drug used on the neonate, the effects of phototherapy must be categorized, and the procedure must be standardized. Further investigations are needed to determine exact in vivo decomposition products, optimal timing of exposure, differences in skin attenuation, toxicity reactions, site of action, and photobiologic and photochemical alterations and interreactions.

Influence of Application Conditions on Lumen Output and Chromaticity Characteristics of Metal Halide Lamps

Influence of Application Conditions on Lumen Output and Chromaticity Characteristics of Metal Halide Lamps

Luminescence bands of molecular oxygen from a tungsten lamp.: The possible role of singlet molecular oxygen in surface catalyzed oxidation

Sharp emission bands superimposed on ordinary incandescent tungsten lamp output have been observed. These definite spectroscopic bands have been tentatively assigned to Single and Simultaneous Transitions in molecular oxygen. An alternative explanation of a perturbed molecular oxygen, [W·O 2], has not been completely ruled out. A possible relation of this novel method of generation of Singlet Molecular Oxygen to heterogeneous catalysis has been pointed out.

Reciprocity failure in films of flash exposed dichromate sensitized polyvinyl alcohol

AbstractThe validity of the Busen‐Roscoe reciprocity law in flash exposed dichromate sensitized polyvinyl alcohol (PVA) films was investigated. It was found that the flashlamp operating conditions were an important parameter in an exposure system, since a spectral distribution shift of the lamp output could be obtained by changing the pulse duration from 0.3 to 2.0 msec. The apparent reciprocity failure obtained by varying the pulse duration while maintaining the energy stored in the capacitor bank fixed was consistent with the spectral distribution shift in the lamp output. When this shift was accounted for there was only a negligible reciprocity failure found over the range of these flash exposures; however, comparison with a steady mercury are lamp showed that the flash exposure cross‐linked the PVA about 200 times more efficiently.