LightTAG Science

Here’s a little about the science behind LightTAG:

The image that forms inside the camera is upside down, just as it is on the retina of our eyes. The quirky orientation is because light travels in straight lines through the small aperture at the front of the camera or pupil of our eye.

Our brains interpret the image on the retina to show 
us the world the right way up (anything else would be 
too confusing). Cameras record the image faithfully upside down.

Light travels in straight lines but can appear to curve round corners in fibre optic cable. The glass fibre acts like a tube inside which the light reflects off the inner walls until it emerges at the end. We have known about these properties of light for centuries but it is only recently we have used the principle for applications as diverse as cables carrying broadband and Christmas tree lights.

All cameras work on the same scientific principals and can be reduced to a box with a hole at the front with some method of detecting light on the inside (such as celluloid in a film camera).
Without the need for batteries or lenses, the young people used their knowledge of light to put together pinhole cameras and create beautiful images like this one.

All of the young people we have worked with have been encouraged to experiment with the camera and different LED lights in the true spirit of scientific investigation. As with scientific discoveries some of the most creative and spectacular results of these experiments have been through happy accident. One of the most common questions heard, from participants and mentors alike, 
has been ‘How did you do that?’

Our eyes are ’tuned’ to see electromagnetic waves in a very narrow range. The electromagnetic waves are what we perceive as colours of the rainbow. Whilst human eyes are particularly sensitive to colours red, green and blue other animals such as bees can see beyond our visible range into the Ultra Violet region.

Learning about aperture size, exposure time, focus 
and sensitivity of the detector (ISO) the young people could experiment with different settings to create a 
range of effects.

We can study the universe using electromagnetic waves beyond the visible region. The thermal camera here uses infra red wavelengths to ‘show’ what we normally perceive as heat. Objects that appear dull 
to our eyes suddenly shine and bright LED lights are almost invisible because they don’t give off heat.

LED’s are a very efficient form of lighting and easy to use for LightTAG because they are small and easy to put together. The LED is taped to a coin battery. The batteries last for a few days giving strong bright colours.
Unlike incandescent light bulbs LED’s use most energy to create light instead of heat making them easy to handle and low in energy consumption.

Light can be blended in a camera in a method similar to mixing paint on a canvas. Light is emitted so adding more colours creates a brighter and whiter light. Paint absorbs light and so mixing more colours creates a duller, darker final colour. The primary colours in light are red, blue and green from which all other colours can be formed.

Light is a form of energy and it is this that allows us to record images inside a camera. Whether we use film stock where light energy causes a chemical reaction, or if we use digital cameras where a CCD turns the light energy to a small electric signal recorded by a processor.
This photo shows a light sensitive material which absorbs ultra violet light causing electrons in the material to move to an ‘excited’ higher level. When the electrons relax back to their original levels a green light is emitted. 
The process can take several minutes over which time the green light slowly fades as 
there are fewer and fewer electrons left in 
their excited state.

White light is made up of all the colours of the rainbow. There are many different ways we can separate the colours, using prisms, diffraction gratings (as shown in the photo) or even using the particles in the air as we see in every sunset and sunrise. There is much information contained in the spectra created which can tell us about the stars in the universe, their distance, temperature and even what they are made of.

LED technology has developed through a knowledge of the structure of materials. In a similar way to the phosphorescent sheet the electrons in an LED are promoted to a higher state by energy from the battery. When they fall back to the ground state, light of a 
specific wavelength is emitted and therefore we get different colours.

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