Stills above taken from the following movie shown here in PhotoStudio 5 'Negative', 'Normal' and colour 'Equalized' enhancement modes;  but strangely the beam of light as described by the witness, only becomes clearly visible in the 'Equalized' mode, and only can be feintly seen in the 'Negative' and is totally invisible in 'Normal'; which all leads me to suspect that what we have here is not just light source, but rather, some kind of Energy Beam!  
Name: CA'
City: london, uk
Date: 25.09.08/1:00-1:11 am
Location: Lambeth, London
Message: This sighting was just amazing and quite different from my other sightings. At the begining I saw how the aerial object I was watching projected a beam of light down from its underside and it moved like searching for something.
At this point I saw it had 2 sources of light; then it moved slowly, mostly from my left to my right, pulsating out virtually the entire colour spectrum from one source of light. I was unable to distinguish any solid structure, only light.
>>>Please Click Here to Download This Incredible Footage<<<


Udate from CA':
Ken,
Here is what I could find/research about beams of light:
 
When it became pale/translucent it looked similar to this one that I found on YouTube:
http://www.youtube.com/watch?v=9xJosPacbYw
 
But when I initially saw it, (I didn't take a pic of it at that stage), maybe for less than a min, I didn't know it was a beam of light but something long, bright and solid, because it looked like this, (not this quick though).):
http://www.youtube.com/watch?v=wtJcDuK6ECc
 
Just wanting to explain to you what I saw.
 
Thanks again,
CA'