Different sources of light ks2: Light Sources · Universe in the Classroom

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Light Sources · Universe in the Classroom

A light source is anything that makes light, whether natural and artificial. Natural light sources include the Sun and stars.Artificial light sources include lamp posts and televisions.

Without light sources we could not see the world around us, however not every object we can see is a light source. Many objects simply reflect light from a light source.

Light Sources is an activity that invites students to investigate where light comes from, how it travels and how it can be used, before they use the power of light to explore the Universe!

Light Sources Teacher Guide

Light Sources Student Worksheet

Full Instructions

Learning Objectives
  • Learn what a light sources is.
  • Identify examples of different types of light sources: natural and artificial
  • Understand we see object because light reflects off them into our eyes.
Materials
  • Printed Light Sources Worksheet per student
Background Information

A light source is anything that makes light. There are natural and artificial light sources. A few examples of natural light sources include the Sun, stars and candles. A few examples of artificial light sources include light bulbs, lamp posts and televisions. Without light sources we could not see the world around us, however, not every object we see is a light source. Many objects simply reflect light from a light source, for example tables, trees and the Moon.

Step-by-Step
  1. Begin this activity by asking your students to name some objects that create light. These are called light sources.

  2. Write the answers on the board in three unlabelled columns: non-light sources, artificial light sources and natural light sources.

  3. Discuss the difference between the objects on the board — which are natural and which are artificial. Do some of them only reflect light?

Light from the Sun includes all the colours of the rainbow.

When this light hits the moon it is reflected back to Earth and enters our eyes allowing us to see the Moon.

  1. Hand each student a Light Sources Worksheet and ask them to complete the first question.

  2. Discuss Question 2 with the students, “How does light allow us to see other objects?” Explain what the diagram below shows (they will have a copy on their worksheet) and then ask them to explain in their own words on their worksheet.

  3. Discuss Question 3, “Can rock or metal become light sources?”. Explain that even rock and metal can act as a light source if they become hot enough, direct their attention to the image a shooting star (meteor) at the bottom of their worksheet, these are both made of rock and metal but we see them shining as they burn up in Earth’s atmosphere.

Conclusion

Invite your class to discover the brightest light sources in the Universe – stars! Using LCOGT’s robotic telescopes you can take pictures of stars, galaxies and star clusters that are so bright they can be seen from billions of light years away!

Curriculum Links

KS2 Science in the Welsh National Curriculum
“How things work: how light travels and how this can be used.

Learn about Light & Heat

Science Lesson

All About Light

  • Where does light come from?

Most light comes from heat. When something gets very hot, it usually gives off light. Some examples are a campfire, a stove burner, and the flame of a candle. They all produce heat and light! The largest and most important source of light we have is the Sun. (Read more about that below.) Most lights that we use come from electricity and light bulbs.

  • Is all light hot?

No, some kinds of light do not come from heat. Some examples are the light inside a firefly and the light in a television. Can you think of more?

  • How does light get around?

Light always travels in a straight line for as long as it can. When it hits something that it can’t go through, like a wall or a piece of cardboard, the light goes in a different direction. When you turn on a lamp in your room, light rays from the light bulb spread out all over the room and light it up so you can see.

  • Can light shine through things?

The Sun

The sun is the biggest, brightest, and hottest source of light available to us on the earth. Did you know that the sun is actually a star? The outside of the sun (its surface) is covered with very hot gases. The different gases mix together and cause reactions that are called nuclear reactions. Nuclear reactions create a lot of energy, which makes the sun very hot. The heat creates a lot of light too. Did you know that the sun is so bright that it will damage your eyes if you look directly at it? The light from the sun can also hurt your skin. Have you ever had a sunburn? Although sun rays can hurt our bodies if we aren’t careful, nothing would be able to live on the Earth without the energy (in the forms of heat and light) we get from the sun! Click here to see a close-up picture of the Sun from NASA.

Questions and answers about the sun:

  • How big is the sun?

Our sun is about 1. 4 million kilometers in diameter (across its middle)! That is 109 times as big as earth.

To help your kids understand how big the sun is compared to the earth, help them count out 109 Cheerios and then line them up in a straight line on the floor. Explain that if Earth were as tiny as 1 Cheerio, the sun would be as big across its middle as the line of 109 Cheerios!

  • How far away is the sun?

It is 93 million miles away from earth. How far away do your friends live? Most of them probably only live a few miles away from you!

  • How long does it take for the sun’s light to travel to us?

It takes about 8½ minutes for light from the sun to get to us here on Earth.

Science Projects

What We Know About Light

Make a poster with your children of all the things they know about light. Label it “Things We Know about Light.” They can decorate the poster with pictures of things they listed. Here are some questions to ask:

  • What things can you think of that produce light?
  • How many more things that make light can you find around the house?
  • Are there any living things that make light?
  • What would it be like if you didn’t have any light?

There is much more to learn about light than what you will find here. If you plan to continue studying light, make another list for “Things We Want to Know about Light.” If you ask a question that your kids don’t know the answer to (or if they ask you one that you can’t answer!), add it to this poster. Then make a third list titled “Things We Have Learned about Light” and use it to review what you have learned.

Experiment with Light

Demonstrate how light rays travel with this experiment for young children. Light will move in a straight line unless a material that it can’t travel through blocks it. Then the light ‘bends’ and moves off in another direction.

What You Need:
  • Different materials to test, such as a sheet of clear plastic wrap, aluminum foil, tissue paper, shirt or piece of cloth, a book, a glass of water, etc.
  • a flashlight
  • a dimly lit room with a blank wall
What You Do:

What will happen when you shine a flashlight on different materials? Will light pass through or bounce off and go in a different direction? Have your children make a prediction about each material. Then, to test their predictions, hold each object, one at a time, a few feet in front of the wall. Shine the flashlight at the object (towards the wall). Observe what happens. Does any light reach the wall? Is it less light than without the object in front of the flashlight? Discuss how light can pass through some materials but not others. When light rays cannot pass through a material, they bend and go off in another direction. Can you see the light bending away from any of the materials that block it?

Types, features, advantages and disadvantages of light sources

There are currently 5 types of light sources:

  • Incandescent lamps
  • Halogen lamps
  • Fluorescent lamps
  • High pressure lamps
  • LED lamps

900 02 Let’s consider each of them in more detail.

Incandescent lamps

The principle of operation of these light sources is to heat up a tungsten coil placed in a flask. Practice has shown that most of the energy of incandescent lamps is spent not on lighting, but on heating. As a rule, their service life does not exceed 1000 hours. Despite the fact that today humanity is gradually abandoning uneconomical FLs, about 15 billion such lighting sources are sold in the world per year. The reason for this is the habit and low cost of the product.

Halogen incandescent lamps

Halogen lamps are a modern type of incandescent lamp that is well known to interior designers. New technological solutions, such as the addition of halides to the lamp bulb, the use of special quartz glass, reflectors, have allowed halogen lamps to occupy a separate class of light sources. Thanks to the installed reflector, it became possible to control the width of the «beam». However, the disadvantage of this light source is obvious: heating during operation, which narrows the scope. In addition, «halogens» are characterized by a relatively short service life: 2000-4000 hours.

Fluorescent lamps

These lamps are low-pressure discharge lamps made in the form of a cylindrical tube with electrodes filled with mercury vapor. The principle of operation is the appearance of an electric discharge and its effect on mercury vapor, which emit UV rays, thereby affecting the phosphor deposited on the tube walls. In turn, the phosphor emits visible light. The main advantage of such light sources is their long service life: up to 20,000 hours. However, fluorescent light sources depend on the ambient temperature, which limits their use.

High-pressure discharge lamps

The principle of operation consists in the glow of the filler located in the discharge tube under the action of arc electric discharges. The characteristics of these light sources can be varied by changing the composition of the gas in the injection chamber. Among the advantages of high-pressure discharge lamps are high luminous efficiency, relatively low cost and fast payback periods. The disadvantage is the low stability of the parameters during the service life, but today this is overcome with the help of lamps with a ceramic burner.

LED lamps

LED light sources are semiconductor devices consisting of two semiconductors connected together. When current passes, one of the materials receives an excess of electrons, and the other receives a lack of them. Electrons begin to move to vacant places, thereby generating light and heat. Today, LEDs are leaders in automotive, aviation and lighting equipment. In addition, they are characterized by a high potential life and customization. However, LED light sources also have their disadvantages: efficiency and lifetime depend on the junction temperature.

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Light sources

Artificial light sources — technical devices of various designs that convert energy into light radiation. Light sources mainly use electricity, but chemical energy and other methods of light generation are also sometimes used (for example, triboluminescence, radioluminescence, bioluminescence, etc.).

Light sources most commonly used for artificial lighting are divided into three groups — discharge lamps, incandescent lamps and LEDs. Incandescent lamps are thermal light sources. Visible radiation in them is obtained as a result of heating a tungsten filament with an electric current. In gas-discharge lamps, the radiation of the optical range of the spectrum arises as a result of an electric discharge in an atmosphere of inert gases and metal vapors, as well as due to luminescence phenomena, which converts invisible ultraviolet radiation into visible light.

HID lamps are preferred in industrial lighting systems. The use of incandescent lamps is allowed if it is impossible or economically inexpedient to use gas discharge lamps.

Main characteristics of light sources:

Rated supply voltage U, V;

electric power W, W;

luminous flux Ф, lm;

Luminous efficacy (the ratio of the luminous flux of the lamp to its power) lm/W;

service life t, h;

Color temperature Tc, K.

Incandescent lamps

An incandescent lamp is a light source in which the conversion of electrical energy into light energy occurs as a result of incandescent electric current of a refractory conductor (tungsten filament). These devices are intended for household, local and special lighting. The latter, as a rule, differ in appearance — the color and shape of the flask. The coefficient of performance (COP) of incandescent lamps is about 5-10%, such a proportion of the electricity consumed is converted into visible light, and most of it is converted into heat. Any incandescent lamps consist of the same basic elements. But their size, shape and placement can be very different, so different designs are not alike and have different characteristics.

Lamps are available that are filled with krypton or argon. Krypton is usually shaped like a «fungus». They are smaller in size, but provide a greater (about 10%) luminous flux compared to argon ones. Lamps with a spherical bulb are designed for lamps that serve as decorative elements; with a bulb in the form of a tube — for illuminating mirrors in closets, bathrooms, etc. Incandescent lamps have a luminous efficacy of 7 to 17 lm / W and a service life of about 1000 hours. They are light sources with a warm tonality, therefore they create errors in the transmission of blue-blue, yellow and red tones. In the interior, where the requirements for color reproduction are quite high, it is better to use other types of lamps. It is also not recommended to use incandescent lamps for illuminating large areas and for creating illumination in excess of 1000 Lx, as this releases a lot of heat and the room «overheats».

Despite these limitations, these fixtures are still a classic and favorite source of light.

Halogen incandescent lamps

Incandescent lamps lose their brightness over time, and this happens for a simple reason: the tungsten evaporating from the filament is deposited as a dark coating on the inner walls of the bulb. Modern halogen lamps do not have this drawback due to the addition of halogen elements (iodine or bromine) to the filler gas.

Lamps come in two forms: tubular — with a long spiral located along the axis of the quartz tube, and capsule — with a compact filament body.

Small household halogen lamp bases can be threaded (Type E) which will fit regular sockets and pinned (Type G) which require a different type of socket.

The luminous efficacy of halogen lamps is 14-30 lm/W. They are warm-toned sources, but their emission spectrum is closer to the spectrum of white light than incandescent lamps. Thanks to this, the colors of the furniture and interior in warm and neutral colors, as well as the complexion of a person, are perfectly «transmitted».

Halogen lamps are used everywhere. Lamps with a cylindrical or candle-shaped flask and designed for a mains voltage of 220V can be used instead of conventional incandescent lamps. Mirror lamps, designed for low voltage, are almost indispensable for accent lighting of paintings, as well as residential premises.

Fluorescent lamps

Fluorescent lamps (LL) — low pressure discharge lamps — are a cylindrical tube with electrodes, into which mercury vapor is pumped. These lamps consume significantly less energy than incandescent or even halogen lamps, and last much longer (lifetime up to 20,000 hours). Thanks to their economy and durability, these lamps have become the most common light sources. In countries with a mild climate, fluorescent lamps are widely used in urban outdoor lighting. In cold regions, their propagation is hindered by the fall of the light flux at low temperatures. The principle of their operation is based on the glow of the phosphor deposited on the walls of the flask. The electric field between the electrodes of the lamp causes the mercury vapor to emit invisible ultraviolet radiation, and the phosphor converts this radiation into visible light. By choosing the type of phosphor, you can change the color of the emitted light.

High-pressure discharge lamps

High-pressure discharge lamps operate by glowing the filler in the discharge tube under the action of electric arc discharges.

The two main high pressure discharges used in lamps are mercury and sodium. Both give fairly narrow-band radiation: mercury — in the blue region of the spectrum, sodium — in the yellow, so the color rendering of mercury (Ra = 40-60) and especially sodium lamps (Ra = 20-40) leaves much to be desired. The addition of various metal halide mercury lamps inside the discharge tube of a mercury lamp made it possible to create a new class of light sources — metal halide lamps (MHL), which are distinguished by a very wide emission spectrum and excellent parameters: high luminous efficiency (up to 100 Lm / W), good and excellent color rendering Ra \u003d 80 — 98, a wide range of color temperatures from 3000K to 20000K, the average life is about 15,000 hours. MGLs are successfully used in architectural, landscape, technical and sports lighting. Sodium lamps are even more widely used. Today it is one of the most economical light sources due to its high light output (up to 150 Lm/W), long service life and reasonable price. A huge number of sodium lamps are used to illuminate roads. In Moscow, sodium lamps are often used to save money on pedestrian areas, which is not always appropriate due to problems with color rendering.

LEDs

An LED is a semiconductor device that converts electrical current into light. Specially grown crystals provide minimal power consumption. The excellent characteristics of LEDs (light output up to 120 Lm/W, color rendering Ra=80-85, service life up to 100,000 hours) have already provided leadership in lighting equipment, automotive and aviation technology.

LEDs are used as indicators (power indicator on the instrument panel, alphanumeric display). In large outdoor screens and in running lines, an array (cluster) of LEDs is used. Powerful LEDs are used as a light source in lanterns and spotlights. They are also used as a backlight for LCD screens. The latest generations of these light sources can be found in architectural and interior lighting, as well as in domestic and commercial.

Advantages:

High efficiency.

By alexxlab

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