How to See a Rainbow
$0.00
This is one of a set of almost 40 diagrams exploring Rainbows.
Each diagram appears on a separate page and is supported by a full explanation.
- Follow the links embedded in the text for definitions of all the key terms.
- For quick reference don’t miss the summaries of key terms further down each page.
Description
How to See a Rainbow
TRY SOME QUICK QUESTIONS AND ANSWERS TO GET STARTED
About the diagram
An overview of rainbows
Conditions for seeing rainbows
About the diagram
Some key terms
Rainbow colours are the bands of colour seen in rainbows and in other situations where visible light separates into its component wavelengths and the spectral colours corresponding with each wavelength become visible to the human eye.
- The rainbow colours (ROYGBV) in order of wavelength are red (longest wavelength), orange, yellow, green, blue and violet (shortest wavelength).
- The human eye, and so human perception, is tuned to the visible spectrum and so to spectral colours between red and violet. It is the sensitivity of the eye to this small part of the electromagnetic spectrum that results in the perception of colour.
- Defining rainbow colours is a question more closely related to the relationship between perception and language than to anything to do with physics or scientific accuracy.
- Even the commonplace colours associated with the rainbow defy easy definition. They are concepts we generally agree on, but are not strictly defined by anything in the nature of light itself.
- Whilst the visible spectrum and spectral colour are both determined by wavelength and frequency it is our eyes and brains that interpret these and create our perceptions after a lot of processing.
An observer perceives bands of colour when visible light separates into its component wavelengths and the human eye distinguishes between different colours.
- The human eye and brain together translate light into colour.
- When sunlight is dispersed by rain and forms a rainbow, an observer will typically distinguish red, orange, yellow, green, blue and violet bands of colour.
- Although a rainbow contains electromagnetic waves with all possible wavelengths between red and violet, some ranges of wavelengths appear more intense to a human observer than others.
A rainbow is an optical effect produced by illuminated droplets of water. Rainbows are caused by reflection, refraction and dispersion of light in individual droplets and results in the appearance of an arc of spectral colours.
- Rainbows only appear when weather conditions are ideal and an observer is in the right place at the right time.
- Waterfalls, lawn sprinklers and other things that produce water droplets can produce a rainbow.
- A rainbow is formed from millions of individual droplets each of which reflects and refracts a tiny coloured image of the sun towards the observer.
- It is the dispersion of light as refraction takes place that produces the rainbow colours seen by an observer.
- When the sun is behind an observer then the rainbow will appear in front of them.
Sunlight is light emitted by the Sun and is also called daylight or visible light.
- Sunlight is only one form of electromagnetic radiation emitted by the Sun.
- Sunlight is only a very small part of the electromagnetic spectrum.
- Sunlight is the form of electromagnetic radiation that our eyes are sensitive to.
- Other types of electromagnetic radiation that we are sensitive to, but cannot see, are infrared radiation that we feel as heat and ultraviolet radiation that causes sunburn.
Reflection takes place when incoming light strikes the surface of a medium, obstructing some wavelengths which bounce back into the medium from which they originated.
Reflection takes place when light is neither absorbed by an opaque medium nor transmitted through a transparent medium.
If the reflecting surface is very smooth, the reflected light is called specular or regular reflection.
Specular reflection occurs when light waves reflect off a smooth surface such as a mirror. The arrangement of the waves remains the same and an image of objects that the light has already encountered become visible to an observer.
Diffuse reflection takes place when light reflects off a rough surface. In this case, scattering takes place and waves are reflected randomly in all directions and so no image is produced.
- A light source is a natural or man-made object that emits one or more wavelengths of light.
- Natural light sources include:
- The Sun is the most important natural light source in our lives and emits every wavelength of light in the visible spectrum.
- Celestial sources of light include other stars, comets and meteors.
- Other natural sources of light include lightning, volcanoes and forest fires.
- There are also bio-luminescent light sources including some species of fish and insects as well as types of bacteria and algae.
- Man-made light sources include:
- Man-made light sources of the most simple type include natural tars and resins, wax candles, lamps that burn oil, fats or paraffin and gas lamps
- Tungsten lights: These are a type of incandescent source which means they radiate light when electricity is used to heat a filament inside a glass bulb.
- Halogen bulbs: These are more efficient and long-lasting versions of incandescent tungsten lamps and produce a very uniform bright light throughout the bulb’s lifetime.
- Fluorescent lights: These are non-incandescent sources of light. They generally work by passing electricity through a glass tube of gas such as mercury, neon, argon or xenon instead of a filament. Fluorescent lamps are very efficient at emitting visible light, produce less waste heat, and typically last much longer than incandescent lamps.
- LED lights: An LED (Light Emitting Diode) is an electroluminescent light source. It produces light by passing an electrical charge across the junction of a semiconductor. An LED light typically emits a single colour of light which is composed of a very narrow range of wavelengths.
- Made-made lights can emit a single wavelength, bands of wavelengths or combinations of wavelengths.
A human observer is a person who engages in observation by watching things.
- In the presence of visible light, an observer perceives colour because the retina at the back of the human eye is sensitive to wavelengths of light that fall within the visible part of the electromagnetic spectrum.
- The visual experience of colour is associated with words such as red, blue, yellow, etc.
- The retina’s response to visible light can be fully described in terms of wavelength, frequency and brightness.
- Other properties of the world around us must be inferred from patterns of light.
Refraction refers to the way that electromagnetic radiation (light) changes speed and direction as it travels across the interface between one transparent medium and another.
- As light travels from a fast medium such as air to a slow medium such as water it bends toward the normal and slows down.
- As light passes from a slow medium such as diamond to a faster medium such as glass it bends away from the normal and speeds up.
- In a diagram illustrating optical phenomena like refraction or reflection, the normal is a line drawn at right angles to the boundary between two media.
- A fast (optically rare) medium is one that obstructs light less than a slow medium.
- A slow (optically dense) medium is one that obstructs light more than a fast medium.
- The speed at which light travels through a given medium is expressed by its index of refraction.
- If we want to know in which direction light will bend at the boundary between transparent media we need to know:
- Which is the faster, less optically dense (rare) medium with a smaller refractive index?
- Which is the slower, more optically dense medium with the higher refractive index?
- The amount that refraction causes light to change direction, and its path to bend, is dealt with by Snell’s law.
- Snell’s law considers the relationship between the angle of incidence, the angle of refraction and the refractive indices (plural of index) of the media on both sides of the boundary. If three of the four variables are known, then Snell’s law can calculate the fourth.
Diagrams are free to download
Downloads: Slides or Illustrations
DOWNLOAD DIAGRAMS
- SLIDES are optimized for viewing on-screen.
- ILLUSTRATIONS are optimized for printing on A4 pages in portrait format.
SLIDES
- Slides are available in JPG and AI (Adobe Illustrator) file formats.
- Titles: Slides have titles.
- Backgrounds: Black.
- Size: 1686 x 1124 pixels (3:2 aspect ratio).
ILLUSTRATIONS
- Illustrations are available in JPG and AI two file formats.
- Titles: No titles.
- Backgrounds: White.
- Size: 1686 x 1124 (3:2 aspect ratio). So all illustrations reproduce at the same scale when inserted into Word documents etc.
- Labels: Calibri 24pt Italic.
File formats: JPG & AI
DOWNLOAD THE DIAGRAM ON THIS PAGE AS A JPG FILE
- JPG (JPEG) diagrams are 1686 x 1124 pixels (3:2 aspect ratio).
- If a JPG diagram doesn’t fit your needs, you can download it as an AI (Adobe Illustrator) file and edit it yourself.
- JPG files can be placed or pasted directly into MS Office documents.
DOWNLOAD THE DIAGRAM ON THIS PAGE AS AN AI file
- All AI (Adobe Illustrator) diagrams are 1686 x 1124 pixels (3:2 aspect ratio).
- All our diagrams are created in Adobe Illustrator as vector drawings.
- Save as or export AI files to other formats including PDF (.pdf), PNG (.png), JPG (.jpeg) and SVG(.svg) etc.
Spelling: UK & US
We use English (UK) spelling by default here at lightcolourvision.org.
COPY & PASTING TEXT
- After copy/pasting text please do a spell-check to change our spelling to match your own document.
DOWNLOAD DIAGRAMS
- Download AI versions of diagrams to change the spelling or language used for titles, labels etc.
- We are adding American English (US) versions of diagrams on request. Just contact us and let us know what you need.
- When downloading JPG versions of diagrams, look out for JPG (UK) or JPG (US) in the download dialogue box.
Download agreement
DOWNLOAD AGREEMENT
Light, Colour, Vision & How To See More (https://lightcolourvision.org) : Copyright © 2015-2022 : MediaStudies Trust.
Unless stated otherwise the author of all images and written content on lightcolourvision.org is Ric Mann.
ALL RIGHTS RESERVED
No part of this website may be copied, displayed, extracted, reproduced, utilised, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical or otherwise including but not limited to photocopying, recording, or scanning without the prior written permission of MediaStudies Trust.
EXCEPTIONS
Exceptions to the above statement are made for personal, educational and non-profit purposes:
Before downloading, cutting and pasting or reproducing any information, images or other assets found on lightcolourvision.org we ask you to agree to the following terms:
- All information, images and other assets displayed and made available for download on the lightcolourvision.org website are copyright. This means there are limitations on how they can be used.
- All information, images and other assets displayed or made available for download are solely and exclusively to be used for personal, educational and non-profit purposes.
- When you find the resources you need, then part of the download process involves you (the user) ticking a box to let us (at lightcolourvision.org) know we both agree on how the material can be used.
- Please contact [email protected] before considering any use not covered by the terms of the agreement above.
The copyright to all information, images and all other assets (unless otherwise stated) belongs to:
The Trustees. MediaStudies Trust
111 Lynbrooke Avenue
Blockhouse Bay
Auckland 0600
New Zealand
[email protected]
We love feedback
Your name and email address will be used solely to provide you with information you have specifically requested. See our privacy policy at https://lightcolourvision.org/privacy/.
We welcome your feedback 🙂