Light:
From bonfires to lasers
Supports National Curriculum, Key Stages 1D, 3F, 6F
Suitable for years 4,5 and 6.
The time for whole session is about 1 hour 15mins. This can be varied by taking shorter
paths through the material eg by omitting activities in italics or omitting the section on
colour. Choices will depend on the particular needs of the school.
Outline of content
Aims to
 establish what the children already know, using demos and class experiments
 explain that excited atoms give out light in cold objects as well as hot objects
 understand that we see when light travels to our eyes
 understand that darkness is absence of light and we cannot see in true darkness
 find that we see most objects because they reflect light to our eyes
 find that mirrors change the direction in which light is travelling and that the
angle matters
 show white light is made up of colours
 explain primary colours of light are red, blue and green
 investigate coloured materials in different colours of light
 demonstrate and discuss up-to-date applications by linking the children’s
knowledge with their experience.
Points to note:
Please read the notes about risks and agree the assessment with the
teacher before the session!
Cross References
- The slides in the PowerPoint presentation are referenced in the table.
- As the presentation may be running throughout the session some simple slides
provide a suitable background, alternatively switch to a black screen.
- Apparatus details are below the table and are linked to the relevant sections.
- Notes about safety are below the table
- Vocabulary: The presentation uses expressions included in the KS1&2 strategies
http://www.standards.dfes.gov.uk/schemes2/science/?view=get
- NB The phrase ‘excited atoms’ does not occur in these strategies.
Misconceptions – ie - Points that are often misunderstood
 Only hot objects give out light.
 We see by light leaving our eyes as shown in films about robots.
 Blackness is a form of light rather than an absence of light.
 We can see in the dark.
The session should be held in a room that is not brightly lit. Curtains or slat blinds could be shut
but the activities have been planned so that blackout is NOT required as this is difficult to
achieve in most primary schools and also might cause behaviour problems.
Light: from bonfires to lasers
1
2
Activities
Sources
Snap a glow stick so that it glows
brightly. Ask what is happening.
Hazard: see safety notes.
See apparatus list.
Suggest that they are camping
and it is getting dark. How can
they provide some light?
Slides 2 to 5
(Bonfire, sunset, stars and
lightening)
3
Discuss other natural sources of
light.
Slide 6
4
5
Show a toy which uses LEDs.
See apparatus list.
Ask for volunteers to handle the
toy after it has been on for a few
minutes. They should notice that
it is still cold.
Other cold sources of light:
TV
LEDs
Light sticks -Chemical reaction
Phosphorescent plastic
Show slide 7
What is happening?
6
Phosphorescent paper or plastic
Discussion
Encourage answers
such as the stick is
giving out light. Several
sticks might be handed
round then placed
prominently to be seen
throughout the session.
Torches and a fire will
be suggested. Slide 2
Suggest they imagine
going for a walk in the
dark on a moonless
night without torches or
matches. Will there be
any light? (stars)
If it is very dark, when
camping, they might be
lucky to see a firefly,
luminous fungi or a
glow worm.
Discuss that not all
sources of light are hot.
Aims/facts
Objects that give
out light are
called sources of
light.
Hot objects emit
(send out) light.
Light travels
from a source.
Sources of light
vary in
brightness
Some sources of
light are cold.
Point out that the light
sticks are still cold after
giving out light for
several minutes.
(Remember that the
moon is not a source of
light.)
Explain that everything
is made up of tiny
particles called atoms.
After atoms are heated
or have been excited in
some other way, they
give out light.
It is possible for some
materials to take in
Light is given out
by atoms.
7
How do we see a source of light?
Light goes from a source to our
eyes. Our eyes then send
messages to our brains that
enable us to interpret the pictures
detected by our eyes.
Slide 8
8
Ask whether we can see anything
if we are in a completely
blackened room?
Take a vote on this.
Slide 9
Hand out the black bags – one to
each group.
They should put a few small
objects into the bags.
The children should look into
their bag, one at a time holding
the bag close to their faces.
Then they should shine a torch
into bag so the objects can be
seen.
See apparatus list.
10 Switch off the torch and they
should see the stickers glowing
brightly but other non luminous
objects will be difficult to see.
9
11 Slide 11
Ask if they think the baby squirrel
is keeping watch as it feeds.
light then give it out
later.
Discuss that if they look
at the room lights light
travels directly to their
eyes.
(If they ask how we see
objects that are not
sources, then explain
that we will come to
that soon but do not
detour at this point.)
Then discuss waking in
the night in the dark.
Those who think they
can see in a completely
dark room will
recognise that there is
usually a small amount
of light (eg through the
curtains) and once our
eyes are used to the
dark we can see when
there is very little light.
Discuss that when there
is no light in the bag we
cannot see inside it.
Then when the torch
shines in the bag they
can see because light
bounces off the objects
in the bag and travels to
their eyes.
Slide 10
Encourage them to ask
about the stickers and
explain that they have
taken in some light and
can send it out later
because they are
phosphorescent.
Discuss that the
squirrel will be
watching who is near
because its eyes are
wide open. It will be
able to see people
because light bounces
We see sources of
light as the light
can travel
directly to our
eyes.
Darkness as the
absence of light.
We need light to
travel to our eyes
to be able to see.
We can see
objects that do not
give out light
when light shines
on them and
bounces back to
our eyes.
Phosphorescent
materials absorb
the light and send
it out later.
off them, and travels to
its eyes.
12 Reflection Slide 12
13 Slide 13
Allow light from the slit slide to
shine on a non reflective surface
e.g. a white board or sheet of
pale cloth. The surface will look
brighter because some light
bounces back to our eyes.
14 Hold a large mirror in the beam
of light from the slide. Change
the position of the mirror until a
bright line is seen on the wall.
Light reflected as a beam.
Slide 14
See apparatus list.
See safety notes.
The light is scattered in
many directions like in
slide 10.
When light
bounces off
something we say
it is reflected.
Explain that the light is
not scattered so the
beam can be seen when
it reaches a surface.
Shiny surfaces can be
used as mirrors, dull
surfaces cannot.
Shiny surfaces
reflect light
better than dull
surfaces. Dull
surfaces scatter
the light.
15 Change the position of the mirror
so that the line on the wall
moves.
Slide 15
A child could be asked
to hold a second mirror
to reflect the beam
again. Discuss that the
direction that the light is
reflected depends on the
position of the mirror.
Point out that we can
predict where the light
will reach the wall
because light travels in
straight lines.
16 Game
A large mirror is fixed or held at
the front of the class and children
take it in turns to point a torch at
it so that the light reaches a
particular object in the room.
The child holding the
torch finds that the
torch should be pointed
at the image of the
object in the mirror.
With a bright torch the
game is possible in a
room that is well lit but
not flooded with direct
sunlight.
They will be able to see
that if the angle at
which the light meets
the mirror is changed
then the direction of the
reflected ray changes.
Discuss that when the
See apparatus list.
17 Slides 16 and 17
Hand out a mirror and a torch to
each group. Ask them to shine
the torch towards the mirror and
look at the reflection and see that
the reflection moves as the torch
moves. See safety notes.
We represent the
light ‘beam’ as
an arrow.
Mirrors can
change the
direction of the
light.
When the angle
at which the
light hits the
mirror is
changed, the
path of the
reflected light
Then each group should prop a
mirror upright on a sheet of white
paper. Then lay a torch on the
paper pointing towards the
mirror. A beam of reflected light
should be seen on the paper. If a
child looks into the mirror the
reflection of the torch is seen.
See apparatus list.
(Slide 18 is an optional extra.)
18 Shadows
These are covered in the
presentation on Sunlight.
However, if objects are held in
the beam from a data projector
then they can be explained.
19
20
21
22
23
light meets the mirror at
a small angle it is
reflected at a small
angle etc.
also alters.
(At this stage
children do not
need to know that
the angle of
incidence is equal
to the angle of
reflection.)
This should only be
covered if particularly
requested. Points to
cover are the factors
which might affect the
size and position of the
shadow.
Discuss the fact that the White light can be
Colour
(Use slides 19 and 20 as
light falling on the CDs split up into
introduction.) Each group should is white light (not
colours.
shine a torch on a CD to see the
coloured) and ask
reflected colours.
where the colours can
Slide 21
come from. Explain that
white light is made of
See apparatus list.
colours.
Slide 22, 23
Encourage the children
Show the slide of the rainbow.
to compare these effects
with the CDs and
explain that the water
droplets in the air split
the light into colours.
Hold a large plastic sheet of
White light is
diffraction grating in the beam
made from all
from the data projector. Bright
the colours of the
colours will be seen and yet when
rainbow.
it is moved from the beam the
colours vanish.
Slide 24 See apparatus list.
Hand out a small piece of grating The children will see a
per child or per group and switch bright pattern of colours
on a small clear electric lamp
- the colours are in the
bulb.
same order as in a
The children should look at the
rainbow.
lamp through the grating.
Colour disc
Discuss that the colours The colours of
Spin the colour disc holding it
add to give white. They the rainbow add
high so the whole class can see.
might like to discuss
to give white
If possible increase the speed
persistence of vision to light.
slowly until the disc appears
explain the effect.
white. See apparatus list.
See safety notes.
24 Ask if they mix paints. Explain
that there are primary colours in
light (red, green, blue) which are
different to those in paints (red,
yellow, blue) and this leads to
some odd effects.
Slides 25, 26, 27 emphasise the
primary colours and can be used
later. (These colours are called
primary because by adding these
lights one can make all colours
we see.)
25 Show slides 29 and 30. They are
as the children expect from
paints.
Then show slide 31 They find the
yellow surprising.
26 Use slide 32 which provides a
beam of white light and hold up a
coloured transparent film or other
transparent objects in the beam.
See apparatus list.
27 Hold up coloured objects in
coloured light using slides
25,26,27, 33,34,35 to show that
objects look different in coloured
light. See apparatus list
Choose good effects and cover
this quickly without going into
detail.
27 Hold up a dull black object in
coloured beams of light and it
will still look black because it
takes in all the colours of light.
29 Slide 36
Wear a rubber glove to hold up a
string of lit Christmas tree lights
bunched together. Then hold
transparent sheets of coloured
plastic or silk in front of the
Discuss mixing paint
colours - encourage
red + blue = purple
green + blue =
turquoise but they will
also give
blue + yellow = green*
and others that are less
useful.
Primary colours
of light are red,
blue, green.
Explain that the colours
overlap on the slide to
give the effect. (Some
children are familiar
with PowerPoint and
word.)
The words magenta and
cyan might be
introduced.
Discuss opaque and
translucent materials
and therefore the idea of
some light being unable
to pass through some
materials.
red+blue=magenta
blue+green=cyan
red+green=yellow
Translucent
materials allow
some light to
pass through.
(Not all
translucent
materials are
coloured.)
Choose objects such as
a brightly coloured silk
scarves. The IoP red
and yellow women’s
scarf is very effective
for this. Explain that
only some of the light
colours can be reflected.
The light that is not
reflected is absorbed.
Black objects
absorb all
colours.
Explain that some
colours are absorbed
and some can pass
through. Eg only green
light can pass through
green plastic. Red, blue
lights. The appearance of the
lights changes.
See apparatus list.
See safety notes.
30 Slide 37
Explain that research about light
has led to the development of
lasers, which have many uses.
Eg CD players.
31 Slide 38
Explain that in a CD player, the
laser light is reflected by the
smooth sections and scattered by
the pits to give a message, which
is changed to an electrical signal
and then music.
32 Slide 39
and magenta can pass
through magenta
plastic. The activity
should be covered
quickly but gives the
opportunity to reinforce
ideas.
Remind them that
earlier they had learned
that light is given out by
atoms. In a laser all the
atoms can give out light
at the same time so it is
very bright.
Discuss that the CD is
circular because the
smooth parts and pits
are in a spiral pattern.
Scientists keep
finding out new
exciting facts.
Learning about
physics leads to
useful inventions.
Physics is in
everything.
Apparatus
Please read the safety notes below this apparatus list.
1
Glow sticks or glow bracelets etc can be bought cheaply on the web eg glow glasses for
39p each – cheaper if more than 10 bought Hazard- see the safety notes!
4
Bright toy using LEDs or a miniature torch using a LED.
9
Black bags – enough for one per group of children
Black cloth bags made from dense black material, for example from an old black tee
shirt.
Phosphorescent stickers – available from toy shops and stationers
Torch – one per group. The school could be asked to provide these or the children asked to bring
them.
The bags should be approximately 20 cm x 20 cm or larger. Stick a selection of phosphorescent
stickers at the bottom of the bag the day before the session and then keep the bags in the dark.
When the bags have been given out to the groups, ask the children to put a few small objects into
the bag (eg a pencil sharpener). Check with the teacher before the session that suitable objects
will be available or put some objects in the bags before the session.
When they look inside the bag, (one child at a time) they will hardly be able to see the objects.
Then they should shine the torch into the bag so that they can see all of the objects.
After the torch is switched off they will see the stickers glowing brightly.
14, 15, 16
Mirror
Demonstration
A large mirror to reflect light from the PPT slide – at least 50 cmx50 cm- use a
household mirror
A second large mirror – preferably plastic
17
Class experiment
For each group:
 Torch
 Mirror (Schools usually have mirrors which are also used in maths.)
 Block or support to keep mirror upright
 A sheet of white paper
19
Several CDs to hand round for the children to see the colours in the reflected light.
21
Diffraction grating material in the form of plastic film can be obtained from Edmunds
Optics (USA) two sheets ~ 15x30 cm2, 1000 lines per mm for ~ £8 plus postage.
Keep one sheet whole for demonstrations and cut the second into pieces for the
children to use. (If the small pieces are framed with card they will not be lost.)
23
Colour disc demonstration
 Hand held electric food mixer or travel fan
 card
 blu tac
Copy the colour wheel below, print it and glue the disc to a circle of card.
(To enlarge the wheel, left click on it and stretch the corner dots that appear.)
I used a hand held food mixer with only one beater attached and fastened the card
to it using a large lump of blu tac.(String can also be tied through small holes in the
card to fasten it to the beaters or fan to ensure that the disc does not fly off at high
speed.) It was possible to increase the speed slowly so that the children could see
the colours blending more and more until at the highest speed the disc appeared
white.
Alternatively attach the disc to the end of a travel fan or the bit of an electric drill.
26
Samples of coloured transparent plastic – I found that brightly coloured transparent
wallets for A4 papers were suitable and much cheaper than colour filters. I chose
the brightest colours and used the wallets fastened.
27
Collect a few large brightly coloured objects that you have available - I used posters
and silk scarves. Use the slides to show that they objects look different in different
colours of light.
Eg:
a yellow object in red light then green light.
a blue object in red light
etc
Note - an explanation of why yellow and blue paints mix to give green
(this works for only some blues)
- yellow paint reflects red + green light
- some blue colours are actually blue + some green
- mixing paints is colour subtraction
- the reflected colour is the colour that can be reflected by all the paint
- hence green is seen.
29
A string of coloured Christmas-tree lights
(You will need to check that there is a convenient mains socket before the
presentation.)
Samples of coloured transparent plastic as in 26
_______________________________________________________
Safety Notes
Do not use laser pointers as some of them are not safe.
It is dangerous for the children (or anyone else) to look at the Sun.
Light sticks:
If the outer casing of a light stick is punctured the fluid is hazardous because it:
 may contain tiny shards of glass
 should not be in contact with eyes
 should not be ingested
 can cause irritation
 may cause an allergic reaction
 may stain clothing, skin etc and should be washed off with soap at once.
Light sticks cannot be reactivated once the chemical reaction has ceased and
should be disposed of so that small children cannot have access to them.
Mirrors
 Make sure that mirrors do not have sharp edges.
 When using the large mirror hold it personally and do not ask the children
to help.
 Use plastic mirrors if possible for group work.
 Do not reflect sunlight with mirrors. If sunlight is reflected into a child’s
eye it can cause damage.
Fasten the colour disc to the mixer or fan securely so that it does not fly off.
The Christmas tree lights are connected to the mains electricity supply and so
should not really be handled by anyone while powered. To make this safe (and to
emphasise the risk) the hand holding the lights should be protected by wearing a
rubber washing-up glove.