Colour mixing

Public summary: 

How many colours can you make? With our coloured lights, find out how you can make every colour imaginable from just three colours, find out how your computer monitor works and get to see some really funky shadows!

Dimmable, focussed red, green and blue lamps for experimenting with light colour mixing
Useful information
Kit List: 

3 lamps with LED bulbs and focussing optics
Bench power supply (6V MAX PLEASE)

Packing Away: 

Lamps should be packed in experiment box, power supply to be packed away separately in power supplies box

Frequency of use: 

The three lamps in this experiment each contain an LED focussed to produce a tight, reasonably even circle of light that can be projected onto different surfaces. The lamps each produce a different colour (red, green, blue) and can be individually dimmed. This allows you to play with producing different colours by adjusting the intensities of the different lights.

Suggestions for explanation:

- Mixing a colour – get the children to choose a colour and let them work out how to make it.
- Demonstrating how the primary and secondary colours (of light) are produced – space the three colours so they slightly overlap to produce three circles of red, green and blue, with cyan, magenta and yellow where two colours overlap and white where all three do
- Fooling the eye – LEDs are fairly monochromatic – their spectrum is not very widely spread about the peak wavelength. Because we expect light to appear as it does from a 6500K light source (the sun), it is possible to confuse the eye when dealing with monochromatic light. For example, mix the lights to produce a white(ish) colour, then put a brightly primary coloured object such as a tomato underneath. Because, the surface will directly reflect a large proportion of one colour, it will appear unexpectedly bright.
- Funky shadows – shine the lamps at a wall or other white surface from some distance away. Observe the multiple shadows of different primary and secondary colours that can be seen. This works best with a wide separation between the lights.
- This is a new experiment – if you think of something interesting to talk about, please write it below!

Risk Assessment
Date risk assesment last checked: 
Mon, 01/01/2018
Risk assesment checked by: 
Date risk assesment double checked: 
Sat, 03/02/2018
Risk assesment double-checked by: 
Andrew Sellek
Risk Assessment: 
DESCRIPTION Using 3 focussed, dimmable LED lamps in red, green and blue to investigate colour mixing
RISKS 1. Light from LEDs can be intense.
2. Power is dissipated by electronics. Lamp and base may become slightly warm in use and hot if excessive input voltage is used (6VDC MAX)
3. Lamps may topple if knocked
4. Electrical cables present trip hazard
5. Circuit is designed to operate from a 5V supply and is not designed to handle more than 15V under any circumstances. There is no electric shock risk from this low voltage circuit, but it should not be operated outside its specifications to avoid possible overheating.
ACTION TO BE TAKEN TO MINIMISE RISKS 1. The majority of LEDs are considered to be class 1 and do not pose a risk to sight ("safe under all conditions of normal use"). These lamps use 3W Philips Luxeon III LEDs, widely used in a range of consumer products. Whilst the beam is focussed to about 10 degrees, the lumen output is much lower than more modern devices and considerably more powerful and focussed devices are readily available in products such as bicycle lights. The lamps should not, therefore pose a risk to sight even if someone were to look directly into the source.
Do not allow people to look directly into the beam. Natural aversion should be sufficient in most cases, but demonstrator to keep control of lights and if necessary switch off power.
2. Children warned that the lamps may get hot, and instructed to handle lamp at base if moving it about. The correct voltage MUST be used.
3. Lamps are modified desk lamps. Some base weighting was removed in construction, but the modified lamps are not required to support the weight of a bulb. This does not greatly reduce stability but does mean less effort is required to knock them over than may be expected. Conversely, should the lamp be knocked over, damage or injury is unlikely – the plastic LED and lens assembly is practically indestructible in normal operation. Lamps should be used on a flat, level surface.
4. Try to keep cables out of thoroughfare. If cables must be placed somewhere people are likely to be walking, tape them down.
5. To avoid overheating, lamps should not be covered during operation. A 5VDC (nominal) input voltage should be used, maximum 6VDC. UNDER NO CIRCUMSTANCES MUST MORE THAN 15V BE APPLIED TO THIS CIRCUIT.
ACTION TO BE TAKEN IN THE EVENT OF AN ACCIDENT 1. In the event of a person being dazzled by lights, switch off lights and get them to sit down until they have recovered. Check they are ok before letting them walk around in case they walk into something!
2. In the event of a burn call first aider. In the event of fire, follow procedures in venue RA (raise alarm, evacuate,...)
3. In the event of injury, call first aider.
4. In the event of injury, call first aider.
5. If the circuit is damaged during use (abuse, misuse, overvoltage etc.), switch off all power immediately and do not use again until it has been checked by a competent person.
This experiment contains mains electrical parts, see separate risk assessment.
This experiment is sometimes run in a darkroom, see separate risk assessment.
Publicity photo: