Changes

=== Daylight ===

Light of around 555 nanometres is accepted as the most efficient level of light for daytime vision. But recent research has shown that we also have biological receptors for non-visual response peaking in the blue wavelength range of 446-477 nanometres, a range abundant in clear daylight. Researchers at Brown University in 2002 discovered that non-visual ganglion cells in the eye detect sky-blue light to set our internal clock.

Energy efficiency is the amount of light output generated per watt of input energy consumed. This is important because it directly affects the size of our electrical system. The main choices in types of light in order of efficiency are:

* LEDs post-2007

* Fluorescent

* Halogen

* LEDs pre-2007

LEDs have had a very high profile in the energy market for some time. But until recently they did very poorly in energy efficiency and were very expensive. Fluorescents were best, producing about 30-100 lumens per watt, while halogens produced 10-18, and incandescents 8-15. In 2014 mid-market colour-corrected LEDs were running 53-59 lumens per watt; while uncorrected ones were in the 80s.

Newer LEDs are grouped in clusters with diffuser lenses which have broadened the applications for their use. Without a difuser LEDs are very directional.

Ongoing research has dramatically improved the efficiency of LEDs; although this is only starting to appear in production versions. LED efficiency improved dramatically in 2006. Nichia Corporation of Japan demonstrated white LED prototypes with an efficiency of 113 lumens per watt. The industry target is 100 lumens per watt, which is better than fluorescent tubes. The Nichia work was partly funded by the UK Department of Trade & Industry. (White LEDs are actually blue in wavelengths of 450 nm – 470 nm.)

In addition, LEDs produce no discernible heat and are more robust than fluorescents and incandescents. LEDs have become the lighting of choice for many marine applications.

In a low voltage DC system, their driving system is simple and cheap compared to a fluorescent, which requires an oscillating ballast circuit. LEDs use a simple voltage-dropping resistor. They are tough and resistant to shock and vibration. They are safe near explosive gases and liquids. In a marine installation, use a dual-pin ungrounded LED. Until recently LEDs were rated in millicandela (mcd), as measured at the light source, not lumens. This made direct comparisons with other light types fuzzy. (One lumen is approximately 79.5 mcd.)

=== Fluorescents ===

Prior to breakthroughs in the efficiency of LEDs, fluorescent lamps were the clear winners in energy efficiency. They last about 34,000 hours and have low heat output.

Fluorescents have electrodes at both ends of a tube coated inside with phosphor. Inside the tube, a gas contains argon and mercury vapour. A stream of electrons flows through the gas from one electrode to another. This excites the mercury atoms, giving off ultraviolet photons. In turn these excite the phosphor, giving off visible light.

==== Compact Fluorescent ====

=== Halogen ===

Sir Joseph Swann invented them in the 1870s; although most Americans credit Thomas Edison. Watch for improved versions using deposited carbon nanotube filaments by 2009. This may not matter since many governments are banning tungsten bulbs. Australia is targeting 2010, the USA 2012-2014.

== Application ==

In the pilothouse, use blue-green (507 nm) or turquoise (495 nm) LEDs for night vision. Eight percent of males are red-green deficient [8], and will be groping blindly with low-level red or green night vision lights. (Women have an extra strong response to red-orange.) Even a higher percentage may have temporary alterations in perception of blue under varying conditions. Most people over 45 suffer from reduced light transmission into the eye.

[[Category:ElectricalLightingGeneral]]