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I can’t be the only devious so and so to consider flooding hardware store customer review web pages with 0 out of 5 star ratings for rubbish external lights, plus a few choice comments, can I ?
Hi Callum, I was using a 10″ Dobsonian, so I had to let the image drift across the field of view. That’s how I noted the “blind spot”. Otherwise the view was as expected, showing the usual Fraunhofer interference pattern. To clarify, I didn’t see the interference pattern disappear as a result of the double, but that might have been because the slit spacing was not set quite right. More puzzling was the star (ie. its pattern) disappearing completely from view at the blind spot. That was unexpected. Unfortunately I didn’t have presence of mind to check whether it disappeared on the opposite side of the fov as well.
A programme is underway to replace all of the streetlights in Gloucestersire with LED lamps. I understand that dimming will occur between 10pm and 5am for some, whilst others will be switched off after midnight. Gloucester is among the first locations to undergo the switch, and the county council intend to assess any change in skyglow photographically.
My own location seems to be as much affected by the illumination of businesses and sports facilities as by streetlights. Nevertheless the Gloucestershire programme is a significant development.
The trend seems to be towards the use of white LED lamps. Filters such as UHC filters will block much, but not all, of the light emitted from these lamps. This is because white LEDs have a continuous spectrum across the visible range.
This recent study may be of interest:
http://m.jech.bmj.com/content/early/2015/07/08/jech-2015-206012
