The unit for measuring the rate at which light energy is radiated from a source is the?
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Answer is D. Candela\n Candela is the luminous intensity, in the perpendicular direction, of a surface of 1/600 000 square meter of a full radiator at the temperature of freezing platinum under a pressure of 101325 newtons per square meter.  \n\nA is wrong. Angstrom is the unit of wavelength.\n\nB is wrong. Lux is unit of luminous of a surface area which receiving light from a source, emits it.\n\nC is wrong. Lumen is the light emitted per second within a unit solid angle by a uniform POINT source of light.  1 cd = 1 lm sr^ (-1)
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phosphorescence, this link should tell you.
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One example to measure the speed of red light is to use equipment that includes a LED (light-emitting diode) that emits a regular series of pulses of red light that are only 20 nanoseconds in duration.\n\n    (A nanosecond is one-billionth of a second or 1/1,000,000,000 second. It is also written as 10-9 seconds, 10^-9 or 1e-9, where the -9 indicates the number of zeros in the denominator.)\n\nThat means the pulse of light blinks on for 20 billionths of a second or 20/1,000,000,000 second and blinks 40,000 times per second. Having such a short pulse allows the scientist to measure the difference in time it takes to travel two different paths. If the duration was longer, the distance traveled would have to be longer.\n\nBy splitting the light beam with a half-silvered mirror, one beam travels to a mirror 10 meters away and then back to a photodiode detector. The other beam is reflected off a mirror only a few centimeters away. The time difference for the two beams is about 67 nanoseconds, which can be displayed on a regular dual beam oscilloscope.\n\nThe total distance the light travels is 20 meters, which equals 0.02 kilometer (20/1000).\n\nThe speed of light is then:\n\nc = 0.02 kilometers / 67*10-9 seconds = 298,500 kilometers per second\n\nThis is a fairly accurate reading and pretty close to the actual speed of 299,792 km/s.
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wavelength = speed of light / frequency\nfrequency = speed of light / wavelength\nf = (3*10^8 m/s) / (615*10^-9 m)\nf = 4.878*10^14 Hz\n\nwavelength = planck's constant * speed of light / energy\nenergy = planck's constant * speed of light / wavelength\nE = (6.626*10^-34 J*s) * (3*10^8 m/s) / (615*10^-9 m)\nE = 3.232*10^-19 J
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For instance, astronauts have attached a mirror to a rock on the moon; scientists on earth can aim a laser at this mirror and measure the travel time of the laser pulse--about two and a half seconds for the round trip, which gives about 3.00E8 m/s for the speed of light.\n\nIts speed can also be derived from Maxwell's equations for the speed of propagation of electromagnetic fields in vacuum.
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It emits two lines \nD1 at 589.592 nm\nD2 at 588.995 nm\n\nboth in yellow region of visible spectra
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Light Amplified Stimulated Emission Radiation
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Light energy is a form of electromagnetic radiation and is found in a segment of the (EM) electromagnetic spectrum. \n\nThe EM spectrum encompasses the entire range of ionizing and non-ionizing radiation extending in frequency from approximately 1023 hertz to 0 hertz, or in corresponding wavelengths, from 10-13 centimeter to infinity. \n\nThis spectrum includes all forms of classical non-ionizing radiation we are familiar with including ultraviolet light, VISIBLE LIGHT, infrared (light) radiation, microwaves, and radio waves. The spectrum also includes ionizing radiation such as cosmic-ray photons, gamma rays, x-rays. \n\nAt eithe end of the visible light spectrum is infared and ultraviolet light and humans cannot perceive these spectrums of light.  Red colored light is longer wavelength of light and visible violet light is shorter wavelength.\n\nFor a cool chart and more in depth descriptin of the EM spectrum check out the Goddard Space Center's special page on this topic. \n\nhttp://imagine.gsfc.nasa.gov/docs/science/science.html   Use the link that says The Electromagetic Spectrum
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The unit would be the volt: http://physics.nist.gov/cuu/Units/units.html
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Used for measuring light intesity. It has a photo-voltaic cell(s) that produce electrity when exposed to light. The amount of electricity is measured to find the intensity of light.
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Simply put:  it is the luminous intensity expressed in candelas. ( the brightness of light compared to a candle)\n\nA candela is a measurement of the intensity of light, used in the International Standard (SI) measurement system. In the modern age, it is technically defined as the intensity in a given direction of a source that emits monochromatic radiation of a frequency of 540 x 10^12 hertz and which has a radiant intensity in the same direction of 1/683 watts per steradian.\n\nThe candela as a unit of measurement grew out of the desire to adopt a standard method to measure light. In the 19th century, each country had its own measure of light, most extremely difficult to reproduce with accuracy. At the beginning of the 20th century, groups of nations began adopting new standards, such as the international candle, which were based on a single type of lamp and much more consistent. Eventually, in the 1930s, it was decided that a more precise definition was needed.\n\nInitially, the candela was defined as the luminous emission of a Planckian radiator, a type of blackbody, at the temperature of freezing platinum (2045 K). This correlated roughly to the light emitted by a typical candle, making it a suitable measure. In the late 1970s, it was determined that the experimental difficulties in creating a Planckian radiator at such high temperatures made the existing definition of candela less than desirable. The new breakthroughs in radiometry allowed scientists to have a more specific definition, and so the current hertz/watts definition of candela was adopted.\n\nOne reason the watt was not initially tied to the candela is the eye’s differences in seeing various wavelengths of light. Since the human eye is less observant of blue and red light, more wattage is needed to produce the same result in the brain as with yellow or green light. This is why the definition of candela is defined as a very specific hertz, unachievable in actual common lighting. There are those who critique the modern definition of the candela for this reason, arguing that it has removed any common-sense understanding of the candela as an actual emission of light.\n\nThe reason the modern definition of candela includes the somewhat bulky 1/683 watts per steradian is to make it conform to the previous definition, in order to avoid any confusion when comparing the modern unit to the historical candela. In this context, the steradian is the cone of light as it emerges from the source, such that it would light up one meter square of the inside of a sphere with a one meter radius.\n\nSince the precise definition is so unwieldy, it is not uncommon in standard usage to see the candela referred to as “roughly” the amount of light generated by a single candle. This definition is perfectly suitable for common usage, as is the translation of 120 candela to roughly the light emitted by a 100 watt light bulb.
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the speed of light(radiation) is a constant and equals the wavelength times the frequency. As wavelength gets longer the freq goes down and vice versa.
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You'll need this number:\n\n1.740×10^17 W.\n\nThis is the solar constant, the amount of energy received at the earth per second per area.\n\nAnd this number:\n\nsigma=5.67x10^-7 J/s/m^2/K^4\n\nThis is the Stefan Boltzmann constant which goes into the (surprise) Stefan Boltzmann law:\n\nJ=e*sigma*T^4\n\nSo, J is the energy received by the body per second per area, and T is it is temperature. The e stands for the efficiency of the body which is the ratio between the power it absorbs and then reemits.\n\nSo, you have an albedo which is an indication of how much light an object reflects from its surface versus how much it absorbs. With these numbers, you should be able to piece together your information with the equation above to get an answer. Let me know if you have further questions.
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It's several million, but it is the lens and reflector that do all the work.\n\nLight is measured in lux or illumination is, candle power is the equivalent of Mega  Tonnes when measuring nuclear yield.\n\nYou may find something here\nhttp://hypertextbook.com/facts/2005/DariaZainullina.shtml\n\nSome have 1000Watt bulbs which is only 10 times more than my bathroom light bulb.
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moving from a higher to a lower energy level releases energy, producing light, but;\nit only produces light in the visible light spectrum when it moves down to level n=2.  if it ends up at another energy level, the light released will be infared, ultraviolet, etc... depending on where it ends up.
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E=mc^2 \nEnergy = mass * (speed of light)^2, c = the speed of light (approx. 186,000 miles per second).
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heat is the measurement of thermal energy