Can lights be modified for the colourblind?
QA few months ago, my friends and I entered the Needles Channel at 0100. Although I have two independent plotters and radar, I prefer to rely on the Mk1 eyeball, together with a dash of common sense for pilotage. To this end, I found the sectored leading light from Hurst Castle to be priceless; its intensity and accuracy meant there was little danger of getting into trouble, especially with the hated Shingles bank to port. It was easy to follow the light and obey any colour shifts we might have engendered by straying off the white sector.
I say ‘we’ but in reality only two out of the three of us could appreciate the worth of the sectored light as the third member is almost completely colourblind and consequently both the red and green sectors appeared to him as if the light had dimmed slightly. Not a good thing in a relatively narrow channel like the Needles.
My friend became quite depressed about it as he had harboured hopes of buying his own vessel and this experience had considerably dented his confidence. It got me thinking – assuming a sectored light originates from a single source and is then split into its relevant coloured beams, could the red and green sectors be made to flash? If, using lenses with LED technology, the green could be made to flash slowly; say at 1Hz and the red be made to flash at say 2Hz, then one would have two ways of identifying both red and green sectors, both by their colour and frequency. This would be a positive boon to anyone suffering colour deficiency and an advancement to safety at sea. Iain Webber
ANeil Jones of Trinity House replies: Trinity House is conscious of the importance of spatial awareness for all mariners. The International Association of Marine Aids to Navigation and Lighthouse Authorities (IALA) – of which Trinity House is a member and contributor – has developed work on oscillating boundaries for sector lights.
These are sometimes used in the UK and also internationally but they do not give the precise cut-off information required for safe sailing, they only indicate increasing proximity to the marked danger; this solution can enhance conspicuity, but it will not, in general, replace the need for accurate sector delineation.
Installing unique flash codes for each sector would add complexity and uncertainty to all colour-sighted mariners and watch keeping officers who are required to have colour recognition.
For the leisure mariner, we suggest that a calibrated hand-bearing compass is used regularly on transit through or down a sector to ensure that accurate positional awareness is maintained.