Light Levels - Understanding Illumination, Measurement, and Distance
This presentation explores the measurement of the quantity of light and the relationship between illumination and distance. You will learn about light, how it can be detected, how its luminous
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About Light Levels - Understanding Illumination, Measurement, and Distance
PowerPoint presentation about 'Light Levels - Understanding Illumination, Measurement, and Distance'. This presentation describes the topic on This presentation explores the measurement of the quantity of light and the relationship between illumination and distance. You will learn about light, how it can be detected, how its luminous. The key topics included in this slideshow are . Download this presentation absolutely free.
Slide1Light LevelsClassAct SRS enabled. In this presentation you will: explore the measurement of the quantity of light explore the relationship between illumination and distance
Slide2Light LevelsIn this presentation you will learn about light, how it can be detected, how its luminous intensity can be measured, and how distance affects the illuminance on a surface . Next >
Slide3Light LevelsEach color has its own specific wavelength, ranging from violet with the shortest wavelength (400 nanometers) to red with the longest wavelength (700 nanometers). All these colors are part of the visible spectrum. Next > White light actually consists of numerous colors, which can be separated by passing white light through a glass prism. This causes the light to refract and disperse. The Visible Spectrum
Slide4Light LevelsNext > The Electromagnetic Spectrum The visible spectrum is one very small part of the electromagnetic (EM) spectrum, which covers an enormous range of frequencies. 10 6 10 7 10 8 10 9 10 10 10 11 10 12 10 13 10 14 10 15 10 16 10 17 10 18 100m 10m 1m 10cm 1cm 1000µm 1mm 100 µm 10 µm 100nm 10nm 1nm 0.1nm 1000m 1000nm 1 µm X-rays Ultraviolet Visible Infra-red Micro- waves Frequency in Hz Wavelength 700nm 600nm 500nm 400nm Radio, tv Long- waves
Slide5Light LevelsThe Human Eye The quantity of light entering the eye is controlled by the size of the pupil , but it is cells in the retina that detect the amount of light and the color. The retina consists of two types of light-sensitive (photoreceptor) cells called rods and cones . These cells react to the different light frequencies, producing different photochemical reactions that send electrical signals to the brain. Next > The human eye can only detect frequencies in the visible spectrum. Pupil Retina
Slide6Light LevelsThe Human Eye Rods can distinguish between different intensities of light, but not between light of different frequencies… … whereas cones allow us to see color. Next > Nucleus Outer segment of cone cell containing photosensitive chemicals Cone Rod Nucleus Outer segment of rod cell containing photosensitive chemicals
Slide7Light Levels1 What is the name given for the part of the electromagnetic spectrum in which light can be seen by the human eye? Question A) Magnetic spectrum B) Visible spectrum C) Frequency spectrum D) Invisible spectrum
Slide8Light Levels2 Rods and Cones are light-sensitive cells in the eye that allow us to see light intensity and color. Which of these two types of cells detects color? Question A) Rods B) Cones
Slide9Light LevelsCrookes’ Radiometer A radiometer consists of a set of vanes, each shiny on one side and blackened on the other. When exposed to light, the vanes revolve. The more light, the faster the vanes revolve. Next > One instrument that can demonstrate the energy emitted by a light source is Crookes’ radiometer. It is difficult to measure light energy with this instrument, as the vanes can move very fast and do not respond quickly to changes. Vanes The vanes are mounted on a spindle in a vacuum.
Slide10Light LevelsIlluminance in lux Resistance in Photoresistor A photoresistor, also called a Light Dependent Resistor (LDR), is a sensor that reacts to the quantity of light falling on it by changing its resistance. The resistance of a photoresistor usually decreases as the ambient light falling on it increases. Next > Modern electronics has given us several light sensing devices.
Slide11Light LevelsPhotodiodes & Phototransistors Photodiodes and phototransistors are light-sensitive semiconductor devices. They can be used in a variety of sensor circuits that detect the presence and the amount of light. Next > Each of these devices reacts to light by controlling the flow of electric current passing through it.
Slide12Light LevelsPhotometry Photometry is the science of measurement of light, in terms of its perceived brightness to the human eye. The human eye is not equally sensitive to all wavelengths of light. Next > In this part of the presentation you will learn about 4 terms that are commonly used in photometry: • L uminous Intensity • L uminous Flux • L uminance • I lluminance Photometry attempts to account for this by weighting the measured power at each wavelength with a factor that represents how sensitive the eye is at that wavelength.
Slide13Light LevelsLuminous Intensity Luminous intensity (I) is a measure of the power emitted by a light source in a particular direction . The unit of luminous intensity is the candela (cd) from the Latin word for “candle”. Next >
Slide14Light LevelsLuminance Next > Luminance (L) is the luminous intensity emitted by a unit area of a light source. The unit of luminance is the candela per square meter (cd/m 2 ). Luminance is often used to measure light emission per unit area from flat, diffuse surfaces, such as video displays. The luminance is a measure of how bright the surface will appear to the eye from a particular angle of view.
Slide15Light LevelsLuminous Flux Luminous flux ( Ф ) or luminous power is a measure of the power emitted by a light source in all directions . The unit of luminous flux is the lumen (lm), from the Latin word for “light”. Luminous flux is often used to measure the useful power emitted by a light bulb. Next > For example, a typical 100 watt incandescent light bulb emits about 1700 lumens. When comparing different types of light bulbs, energy conscious consumers compare the luminous flux of each type of bulb. Roughly the same amount of light can be produced by a 25 watt compact fluorescent light bulb at a quarter the electricity cost.
Slide16Light LevelsI lluminance I lluminance (E) or illumination is the total luminous flux falling on a unit area of a surface. It is a measure of how brightly the surface is lit. The unit of illuminance is the lux (lx), which is the same as lumens per square meter (lm/m 2 ). If 1 lumen (lm) of luminous flux uniformly lights a surface of area 1 m 2 , the illuminance of the surface will be 1 lux. Next > Some typical illuminance values in your everyday surroundings are: Bright sunlight 50,000 – 100, 000 lux Sunset 1 – 100 lux Full moonlight 0.01 – 0.001 lux Classroom lights 100 – 300 lux 1 m 2 1 lumen Illuminance = 1 lux
Slide17Light LevelsArea= 100m 2 = 1 lux 100 lm Lux vs Lumen For example: 100 lumens, concentrated into an area of one square meter, will light up that square meter with an illuminance of 100 lux. The same 100 lumens, spread out over a hundred square meters, will produce a dimmer illuminance of only 1 lux. Next > The difference between the lux and the lumen, is that the lux takes into account the area over which the luminous flux is spread. Area= 1m 2 = 100 lux 100 lm
Slide18Light Levels3 Luminous flux of 100 lumens falls on a flat surface of area 20 m2. What is the illuminance of the surface? Question A) 100 lux B) 20 lux C) 5 lux D) 1 lux
Slide19Light Levels4 What is illuminance measured in? Question A) Candela B) Lumen C) Candela per square meter D) Lux
Slide20Light LevelsEffect of Distance on Illuminance Investigation of illuminance shows that it obeys an Inverse-Square Law , which states that… “… as a light source is moved away from a surface, the illuminance decreases by a factor that is inversely proportional to the square of the distance”. Thus the illuminance of a surface by a source of light 2 m away is 1/4 of the illuminance at 1 m from the source. Next > This can be written as: r 2r 3r 4r 5r I 1 r 2
Slide21Light LevelsEffect of Distance on Illuminance Conversely, for two light sources, one at 1 m from a surface and the other at 2 m, to give the same illuminance to the surface,… …it would be necessary for the source at 2 m to be 4 times as bright as the source at 1 m. Next > 1m 2m
Slide22Light Levels5 If you double the distance between a light source and a sensor, how is the illuminance affected? Question A) The illuminance quarters. B) The illuminance halves. C) The illuminance remains the same. D) The illuminance doubles.
Slide23Light Levels6 If the illuminance at a distance r from a light source is 400 lux, what would the illuminance be at a distance of 2r? Question A) 800 lux B) 200 lux C) 100 lux D) 1 lux
Slide24Light LevelsAfter completing this presentation you should be able to: Summary show knowledge of some of the sensing elements used for the measurement of light. show knowledge of some of the units used in the measurement of light. show knowledge and understanding of the Inverse-Square Law for illuminance and distance. End >