There are two reasons divers carry a light: to see, and to see color. Underwater, these goals have two very different solutions. This is due to the high red light attenuation in water. The advent of high flux LEDs together with a fortuitous coincidence leads naturally to the two-color solution embodied in the Light Diagnostics dive light.

The coincidence is that the wavelength of least attenuation (460 nm, as determined by the US Navy) coincides with the highest luminous flux LED for dark adapted vision. In very dim light the dark adapted eye has a greater blue sensitivity than red. The effect is dramatic. Moving from bright to dark reduces the apparent luminosity of red-orange light by a factor of 18 while it increases our sensitivity to blue by the same factor. The Light Diagnostics dive light with six Luxeon III blue LEDs has a typical underwater output of 145 lumens for the light adapted eye but presents a luminous flux of 2700 lumens (!) to the dark adapted eye. Light meters measure lumens calibrated for the fully light adapted eye only. In the dim light of a dive, the retinal response is somewhere between a light- and dark-adapted response. However, since 95% of the light sensitive cells in the retina (the rod cells) have this blue-enhanced vision, and since blue LEDs combine the most power and the least underwater attenuation, it makes sense to use a blue dive light....for seeing.

To see colors we need to move to the other end of the spectrum and cater to the more red sensitive cone cells which make up the other five percent of the retina and are responsible for color vision. For good underwater color rendering you need to compensate for the red-yellow attenuation by making a red-rich light. While exactly how red-rich it should be depends on the distance to the object, a source color temperature of about 2000 degrees Kelvin provides excellent color rendering over typical dive color-seeing distances.

Such a low color temperature source can not be made with good efficiency (lumens out per watt in) with incandescent, HID or white LEDs. Those three sources only achieve decent efficiency for blue-rich, high color temperature lights. Using six saturated-color LEDs from red to blue we can achieve a color temperature of 2000 degrees and thereby attain excellent color rendering of near to mid distance underwater objects at an underwater luminous flux of 500 lumens in a 25 watt light. This is 30% greater luminosity than six 5500 degree Kelvin Luxeon III white LEDs. And therefore better for seeing colors.

The light weighs 3.75 lbs and lasts one hour between charges. The wall mount charger is included. Extra battery packs and a 12 volt cigarette lighter adapter (for charging in your vehicle) are available. Call Light Diagnostics at (801)293-9266 for a price quote.