QRP Butter Lite

I enjoyed reading your article in WorldRadio. I agree that LED light can be very helpful in low power, low illumination settings. I do have a couple of suggestions that you might want to consider experimenting with. I investigated this subject a few years ago in the context of night lights for a power-limited ocean racing sailboat.

I hypothesized that yellow LEDs would not interfere with night vision much because they are quite monochromatic and their emission spectrum does not overlap the sensitivity spectrum of the blue photoreceptors (night vision) in the eye.

The eye is much more sensitive to yellow, so you get more lumens (usable light) per watt of power than with red (2-3x). Our experience was positive, the helmsmen did not complain any more about yellow lights than about the red lights we used to use.

This is in strong contrast to white lights, which they are very emphatic about turning off. Yellow LEDs have also tested well as safe lights in an x-ray darkroom.

One thing we did to conserve power was to operate the lamps in series. With 9 volts you could operate at least 3 lamps for the same total power consumption as one. We used a current sink (an FET) instead of a resistor, so we shorted out lights we wanted to turn off. The circuit is a little more complex, but the power savings might be important. I have a circuit if you are interested. - Jim Laurino, KD3VD