Technical Tips #71
The ABC's of LED's (Part 1)
The RV industry is moving toward the installation of LED (Light Emitting Diode) light fixtures. In some cases this involves simply equipping the existing lamp fixture with a LED bulb. In other cases, and in future designs, purpose built LED light fixtures that are a sealed unit will become the norm since the life of the LED's can be as much as 60,000 hours. More and more RVers are deciding that they want to upgrade to LED's in their coaches and trailers. There are some basic principles that are important to understand before heading in that direction. In the next few Tech Tips, we'll walk through some of the principal factors about LED's and things to consider if you are considering upgrading or switching to LED lighting.
What are LED's?
Light Emitting Diodes or L.E.D.'s, often shortened to LED's, are electrically a one way control valves that emit light when electricity is passed through them. They will only (emit) light when electricity flows in one direction. In most 12V applications, the standard light bulb has a Ground or Minus 12 volt (-12V) casing and a center pin that is Positive 12 Volts (+12V) often referred to as or the hot side. If the power supplied is reversed in polarity, a typical incandescent light will light, whereas the LED will not, unless the light is designed to compensate for an incorrect polarity. LED bulbs designed to replace a 194 or 921 style bulb(which have two wire pins) can be inserted in either direction into their socket. This bulb style needs to have a reverse polarity compensation to make exchanging them simpler. If they did not, you would insert them into a socket, turn on the power and if it lights, leave it, if not then the bulb would need to be removed, flipped over and re-inserted into the socket to light. This will be an important consideration when converting to LED's. If a new LED bulb does not the issue may be related to polarity and not a defective LED bulb that does not provide light.
Comparison of LED's to Incandescent Lighting
A typical incandescent bulb usually found in an RV will emit light as long as there is sufficient power. It does not matter whether the power is connected incorrectly. That bulb will emit a dull reddish tinged light if the voltage is low (9-11 Volts) with lower intensity and a whiter much brighter light when the voltage rises (12 to 14 Volts). The trade-off is that the life of the bulb is reduced as the voltage rises. If the voltage increases by just a few volts above the 10-14V range it will burn out much quicker. The light from a filament style incandescent bulb provides a wide range of light emission so that this type of bulb will provide adequate light somewhat independent of its mounting position. High quality LED's can operate from 8 to 30 volts with consistent brightness and color of light. Many can be used in dimmer circuits and will maintain their light color over a wide voltage range. The range of dimming from bright to dim will be less than the same circuit controlling incandescent bulbs. For most purposes the
range of dimming is acceptable. Replacement of the existing dimmer and some rewiring of the lighting circuits will increase the range and make it more linear when dimming LED light fixtures. Light output from LED bulbs is more directional with much sharper drop off as the angle from the light source increases. Another benefit of high quality LED's used in RV's is their superior ability to withstand power fluctuations, surges in power and varying power sources without negatively affecting the life of the bulb. This contrasts to the incandescent bulb whose life is dramatically affected by these variations.
Color of Light
Light temperature (and color) is measured in Kelvin(K). To get a better understanding of this measurement, do a search of Wikipedia to understand the concept. As a guideline to color, Daylight is 6500K, whereas a candle or a sunrise/sunset gives light that is 1850K. You can select LED's to use in dimmer circuits; dimming reduces the brightness while maintaining the light color. This feature allows selecting a LED bulb with the light color you prefer. When LED's were introduced, RV manufacturers selected a cool white (4800-5400K) color which many RVers found to be too stark and sterile. Today, the more popular light color is Natural White (4000 to 4500K). Since incandescent bulbs have been used for years in light fixtures, the color comparisons are to these warm white bulbs which have color temperatures in the 3500K range. With the introduction of Compact Fluorescent Bulbs for use in homes many people have adapted to the cooler color temperatures that the typical light emits and while warm white bulbs are available many prefer the Natural White color temperature and this trend will likely drive the use of Natural White replacement bulbs in RVs.
Low Power Requirements
Energy Efficiency is the new normal and LED's feed into this concept. Typical power draw of a LED equipped light is one fifth to one tenth of the power used by the incandescent bulb. As an example the G4 style 10 watt halogen fixture frequently used as a ceiling light in RVs can be replaced with a 1 to 1.5 watt LED. This change dramatically reduces the power requirements and greatly extends the time the light can be used. For those that boondock or dry camp the power requirements for lighting drop significantly, extending battery life and time before charging is required. Using solar panels to maintain a battery bank becomes easier under less than ideal sun conditions when lighting loads is reduced by using LED's. The other benefit of LED bulbs is that they do not product much heat. This feature reduces the load on air conditioning systems and makes adjusting reading light fixtures safer to do. Very little of the power consumed is converted to heat, almost all is converted to light.
Price and Life Expectancy
LED replacement bulbs are not inexpensive. While they have dropped in price by a factor of ten over the last five years they are still more expensive to purchase than the comparable incandescent bulb. Many higher quality LED bulbs are expected to last 45,000 to 60,000 hours implying that they will never require replacement. It is this benefit that is driving the introduction of light fixtures that are one piece with the lighting LED as part of the fixture and no longer being designed to allow "bulb" replacement. In the interim LED replacement bulbs will bridge the gap between the incandescent light fixtures and the one piece units. It is likely that once the conversion is made a replacement will never be required. This is a good advertising ploy however there will be few lights in an RV that will see 60,000 hours of use.
We'll continue this article in the next Tech Tip.