Part 1 - Introduction
This light test was Charlotte's idea. She put together all the hard work in organizing people and getting all the facilities together, and she and Liz worked very hard to get the garage set up.
All I did was put the camera on the tripod (Jonathan took the pictures). I just happened to have the sheet with the numbers on it, so I've put this bit together.
Any plaudits are entirely and completely due to Charlotte. Any mistakes are my fault, and I'm happy to take the blame for them.
The plan was to get a bunch of lights together, battery and dynamo powered, LED and incandescent and see how they performed. How hard could it be?
The lights were to be tested indoors, to allow the light output to be measured and to compare beam shapes, and outdoors to see what how they performed in "real world" conditions.
The battery powered lights all had freshly charged batteries. To ensure consistency with the dynamo lights, Charlotte mounted them all on her bike equipped with a hub dynamo. This bike was then put onto a set of rollers and pedalled up to a constant 15mph/25kph.
As you can see, this was a nerve wracking proposition
Outdoors, when the rollers & tyres were wet, was even scarier. I wouldn't have done it, and I briefed Jonathan to be ready to get out of the way if it went pear shaped.
For the indoors testing, the lights were shone along the length of the bunker onto a target on the end wall, then several things were done:
1. A light reading taken in the centre of the beam, and another at one metre away from the centre (for the incandescent lights this was taken horizontally, for the LED's either horizontally or vertically as their beam patterns tended to be more even). The light meter was set to display EV values, where an increase of 1 results from a doubling of the measured light. I then converted these to absolute values to allow the output of the lights to be easily compared.
2. A picture was taken of the target (obviously lit only by the light) with the camera set to auto. It was hoped that when these pictures were put together they would all be roughly the same brightness so that the beam patterns could be compared.
3. A picture was taken of the target with the camera set to manual exposure. For these, we hoped that when they were put together we would easily be able to compare the brightness of each light.
For the indoor pictures, the camera was set to 1000ASA.
Without pausing to even drink a cup of tea or scoff any Jaffa cakes, bikes were loaded up and a convoy set off (complete with rollers) for the local park where pausing only to scatter the doggers we set out to take more pictures.
The lights were all aimed along the path, which being nice and dark simulated the road, at a point which was about 20 metres away. A little way past that point we put a Brompton to have an example of a real world object that would reflect some light.
Again, two pictures were taken, one on auto to compare beam patterns, and the other on manual to compare brightness.
Although the lights could be easily aimed at the target indoors, outdoors it wasn't as simple. Because most of the lights didn't have a clearly defined centre spot (if they did, they would probably be useless as bicycle lights) they were aimed to try and maximise the amount of path that they lit up, but including the aiming point.
For the outdoor pictures the camera was set to 3200ASA (it's maximum) to reduce exposure time and also reduce the cameras exposure to the rain. That made the pictures a bit grainy, but not so much that it caused problems.