Ramblings of a Techno-Viking

I'm looking for some LEDs

[There are lots of articles about changing RV bulbs to LEDs that tend not be very technical, and lots of technical articles on LEDs aimed at people designing such bulbs and fixtures. This is my attempt to give RVers more technical information.]

Older RVs, like mine, use incandescent auto bulbs for interior lighting. My RV has four types of light fixtures, and I've found two types of bulbs in them: 1003 and 1141. Both use the BA15s base, as does the 1156. Unlike standard 120 volt incandescent bulbs, the life expectancy of these 12 volt bulbs tend to be longer for the higher wattage bulbs, as well as giving more light per watt. Here is information on such bulbs summarized from a couple of makers.

LEDs are diodes that emit light when they conduct. All LEDs are monochromatic (single color) and the color depends on the chemistry making up the diode. The chemistry also determines the voltage needed to get the LED to conduct, so red LEDs are about 1.7 volts, and blue LEDs are about 3.2 volts. White LEDs are blue LEDs that have a dye that fluoresces and creates additional colors. "Bright White" LEDs have less of this dye so more blue light gets through, "Warm White" LEDs have a thicker coating so there is more yellow-green light and less blue. (They tend to be less bright for the same power.) Some other colors of LEDs like pink also use this dye trick.

How bright a light is at a single point is measured in candella (cd). One candella is about as bright as a candle flame. The total amount of light is measured in lumens (lm). Both of these units may be prefixed with the metric prefixes, so you may see a LED rated as 5000 mcd, or about five times as bright as a candle. Larger LEDs used as lighting tend to be rated in lumens. All LEDs will have a display pattern, frequently a cone measured in degrees. Some LED bulbs are made of many small LEDs arranged to mimic the radiation pattern of an incandescent bulb.

White lights have a "color temperature" that measures how reddish or bluish the light is. Incandescent lights work by heating a piece of tungsten white-hot. Cooler is more reddish, hotter is more bluish. White LEDs, like fluorescent light fixtures, only produce light of a few frequencies that the human eye interprets as white since it only samples colors at three (or in rare cases four) frequencies. Sunlight is more reddish at dawn/dusk since it filters through more of the atmosphere. Bluish light can seem harsh and unnatural, since we are not used to seeing things in a (relatively) dim blue light.

LEDs are rated at a maximum current, normally 20mA for small ones. High power LEDs need to be kept cool by using heat sinks and maintaining air circulation. Beyond their rated current, they tend to overheat and have a very short lifetime. Usually they are most efficient at 80-90% of their rated current, as long as they are kept cool. There are several different techniques used to limit the current supplied to a LED:

  • No resistor. Used on disposable LED flashlights that use the battery and wiring resistance to limit current. Tends to have short lifetime.

  • Resistor. Cheap, power wasting, and not good in situations like an RV where the voltage may vary a lot.

  • Constant current regulator. Fairly cheap, wastes power.

  • Switching regulator. More expensive, uses less power. Can create interference with radio and TV signals.

Many LED manufacturers sort their high-power LEDs based on efficiency and color temperature. Low-quantity buyers get what others don't want, or pay significantly more for better quality LEDs.

While most LEDs are rated for 10,000 hours of use or more, some tests of cheaply made white ones have noticed the brightness is significantly less after 1000 hours. This is due to use of inferior dyes. Good ones will have 90% of their original brightness at the rated life.

Some of the places you can buy LED replacement bulbs online are: (I have not done business with any of them, please do not consider this a recommendation.)

Note that none of them give enough specs on their product to allow someone to do a good comparison. It would be nice to have light pattern, color temperature, light output, and efficiency at 10v and 15v. (If it can't handle that voltage range, it shouldn't be used in an RV.) Some of the specs given are doubtful, like having a warm white and cool white equal brightness. Due to this lack of usable specs, and differences in application and opinion, I'll agree with those that recommend buying a few and trying before making a large purchase to replace every bulb in an RV.

When buying a LED bulb to replace an incandescent, you need to find one that fits in your fixture and aims the light in the desired direction. The omni-directional ones almost always aim a good portion of their light where it is not of use.

While the efficiency of a white LED is not as much better than an incandescent as many claim, you need to take into account that the LED will usually have most of its output aimed in one direction. So a 100 lumen LED bulb may put more light on what you want to read than a 400 lumen incandescent. Colored LEDs, such as red used for tail lights, are much more efficient than using a filter over an incandescent light.

When I priced out making my own LED fixtures, minimum orders and shipping make that economicly impractical for less that 100, not including my time and discarded experiments.