Following a blood trail in the dark with a flashlight can be a real challenge. Using a flashlight in the wrong light spectrum can make it more difficult than it needs to be.
LED lights are very popular because the bulbs last a lifetime and they have long battery life. They can also be brighter than some incandescent bulbs. However, typical LED flashlights have a major drawback. They tend to wash out colors, especially reds.
The LED bandwidth is a narrow light spectrum but not quite monochromatic. The royal blue LED will make blood almost appear dark brown. The blue light spectrum is often referred to as a cool tint and the deeper the blue, the harder it is to see red.
A warmer tint in the yellow spectrum is best for seeing blood on the ground in the dark. Incandescent bulbs like the popular Xenon gas bulb work well because they have that yellow tint.
Yellow light is created by mixing the red and green color spectrums. The blood reflects the red spectrum and the green creates a strong contrast. The result is that blood stands out. Blue light will only reflect things that are not red and therefore washout the red.
There are some LED’s that make an exception. LED white light does better than the standard LED bulb, but is not popular in flashlights. There are a few LED flashlights that are carefully color mixed to achieve a realistic color rendering and are comparable to an incandescent bulb.
A couple examples of such LED flashlights are Cabela’s XPG N-series, which boasts an 80 out of 100 on the color rendering index (CRI), and the Terra LUX Light Star. Some flashlight aficionados install a yellow lens over a white LED with satisfying results.
The short slide show provided with this article shows a comparison between a small Xenon bulb in a Mini-Mag flashlight, and a much brighter, one watt, LED flashlight. The Mini-Mag, in-spite of its weaker bulb, shows the contrast of the simulated blood better than the brighter LED.