High Output LED lights do not have the heat problems of Metal Halides, use VASTLY less electricity, often last 50,000 hours, and are very compact. Some LEDs to produce a lot of heat too. If the fan fails, the fixture has to be replaced.
The best LED Fixtures produce less useless yellow/green spectrum light than traditional lights (in aquarium adjusted configurations), as these new technology LED emitters can be selected for the exact wavelength of light, thus almost no or little useless yellow or green light is emitted, so although the LED may seem less bright than some HO lights with the naked eye (such as T5s or MH) the actual output of light energy in spectrums we cannot see (CRI) is much higher, this is why gauging a light by what you see is highly inaccurate.
LED lights with proper Kelvin, Nanometer, PAR & most importantly PURoutput emitters may prove to be more suitable for planted tank lighting and reef tanks because they offer superior flexibility when compared with traditional fluorescent lighting.
When the better LED lights operate, the photometric radiation remains within a narrow band on the electromagnetic spectrum. Specific photometric wavelengths are often beneficial to some aquatic plant life and reef tanks.
Controlling specific wavelengths becomes possible through a basic network of certain colored LED lights connected to a digital LED controller.
Since LEDs emit light only in very specific direction, the installer has the option to illuminate a precise area by simply rotating the polycarbonate tube casing. For this reason the LED does not need to produce as many lumens of light for the same results as most conventional lights. With most conventional lights, many lumens of important light energy are lost due to lack of focus, this includes power compacts and fluorescent lights in general, which need higher lumen outputs to achieve the same lighting parameters. One test shows at least a 166% difference of lumens at 20 inches in favor of the Aqua Ray LED for the same given wattage as compared to a compact Fluorescent.
Another advantage over ALL fluorescent lights, is that LED Fixtures do not loose output over time, most specifically the important PUR wavelengths found in PAR. Fluorescent lights on the other hand do, and this is easily tested by placing a lit one year old fluorescent of the exact same type, next to a lit new one of the exact same brand/type.
With a 6500K fluorescent, the new one clearly has more blue than the more yellow older lamp!