LED Efficiency / Efficacy

One of the most important parameters to the caver is the light efficiency.  The caver wants to carry as small a battery as possible whilst generating as much light as possible throughout the duration of his/her trip.  The efficiency of a light source is measured in lumens per watt.  Florescent tubes produce up to 95 lm/W, Halogen lights produce up to 45 lm/W for high power ratings, but torch bulbs typically used in cave lights produce between 10 lm/W and 20 lm/W.  Tungsten lights are the least efficient, but due to lower costs and longer life are typically used for pilot bulbs.

The high pressure sodium discharge lamp (as used in street lights) is currently the most efficient light source.  The metal halide high intensity discharge lamp (HID) is a variation on the above that although not as efficient is able to produce white light compared to the sodium’s orange light.  Recently, a 10W HID bulb has been developed, it has an efficacy of 50 lm/W; they have been used for high end mountain bike lights.  However, their use for cave lights has not been considered as they are fragile, expensive, and require extensive drive electronics.

We have already discovered that the latest Seoul Semiconductor P4 LED has an efficacy of 100 lm/W, this  is now the most efficient source for white light, just beating the fluorescent tube, which even in its compact form is too large and fragile for cave use.