Changes

All of these types are available in low-voltage DC. Xenon lights are also available in 24 V marine types but are not considered here because of the danger when they break.

LEDs have had a very high profile in the energy market for some time. But until recently they did very poorly in energy efficiency. Fluorescents were best, producing about 30-100 lumens per watt, while halogens produced 10-18, and incandescents 8-15.

Now that LEDs are more competitive, manufacturers are also rating them in lumens.

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.

Invented by A.E. Becquerel of France in 1857, today’s fluorescents are available in full spectrum types with quiet electronic ballasts replacing noisy magnetic ones [5]. Cycling rates have been increased to reduce flicker. Because of the mercury, be careful not to break fluorescents, and dispose of them in an environmentally safe way. The USA Environmental Protection Agency publishes guidelines on what to do if a bulb breaks [57]. Also, don’t use fluorescents in places where you would be at risk if a tube broke. Use LEDs instead.

Cold cathode fluorescents (CCF) are similar in construction to neon tubes and have up to 25,000 hours of service life. They are readily dimmable. Look for models that are listed for marine, RV UL, CSA and CE (Europe), and meet the Ignition Proof test requirements of the United States Coast Guard, as stated in Title 33 CFR 183.410. CCFs are more efficient than other fluorescents but the tri-phosphor fluorescents have the most pleasing colour.

Compact fluorescent lights (CFL) are more robust than tubes. They use only a small amount of mercury, typically less than 5 mg per bulb.

Halogens are a type of incandescent having higher efficiency. The tungsten filament in all incandescent types is very thin, offering high resistance. When a current passes through the filament it glows, giving off light and (mostly) heat.

Halogens are enclosed inside a small quartz lamp containing halogen gas, which increases the light output. Halogens, like most incandescents, have a very natural light. The halogen gas allows the filament to be run much hotter, giving off more light per watt. It also combines with the tungsten in the filament, giving it a longer life by re-depositing vaporized tungsten.

Standard incandescents are very inefficient. About 90% of the energy given off is in the form of wasted heat. They yield about 13 lumens/watt and have a life of 750-1000 hours.

Sir Joseph Swann invented them in the 1870s; although most Americans credit Thomas Edison [6]. 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 ==

Finally, we come to application, how we use these light types. The main applications are: