Light-emitting diodes, or LEDs, are at the forefront of modern illumination for every purpose imaginable, because of their high efficiency, long life, fast switching capabilities, and vibrant color spectrum possibilities. Every year, smaller and smaller LEDs are developed that produce more and more light, as a function of the power consumed. The high brightness potential is one of the main reasons many auto manufacturers are replacing incandescent lighting fixtures with LED versions, whether it is the 3rd brake light, tail lights, interior lighting, or even the headlights.
Lumens. The brightness of the light is usually measured in lumens, or the total amount of light generated. Lumens are derived from luminous flux, which is the total power of light, which is why high-power bulbs are sometimes called "high-flux," To measure lumens, an LED is placed inside a sealed reflective sphere, known as an integrating sphere, and its light is bounced around in all directions in the sphere (integrated) so its flux can be measured at one point, and calculated into lumens based on the size of the sphere. LEDs vary widely in their brightness potential and can be "dimmed" by running at a lower current. (Note: the reason some commercial LED bulbs cannot be dimmed is because of the power controller in the bulb, not the LEDs themselves. All LEDs can be dimmed with the right power supply.)
Candelas. You may see some LED lights measured in mcd, or millicandelas. The candela is a measurement of the total light generated and focused in one particular direction. This is why you might see a flashlight rated in candelas rather than lumens- it is more useful to know how much light is focused on the flashlight, not the total light, which includes some light dispersed in all directions.
Lux. Another measurement of light is lux or the light measured in 1 square meter of the output area. For example, if you mark off one square meter on your garage, and measure all the light that goes into that area when your car is exactly 10 feet away from it, you would have the lux measurement at 10 feet, straight-on, of your headlights. As you can see though, its somewhat difficult to measure lux along with a particular output, and you must factor in how far away the source of light is. Lux ratings are useful for light housing manufacturers, as they want the highest lux available straight-on to light the road ahead, but they also want some lux measurement downwards directly on the road.
Just because a bulb has a higher lumen output, doesnt mean it will "appear" brighter when you look directly at it. Looking directly at the source of light will tell you the lux, or amount of light that specifically reaches your eye. Some LED bulbs are designed with projectors to focus the light in one direction, and that will make them very bright in one direction, or a high lux, but from another angle, the brightness will decrease sharply.
Lux is not a good measurement for automotive use, because automotive housings are designed for use with incandescent bulbs, which evenly distribute light in all directions. Your different housings are designed for different purposes- for example, a headlight will collect and focus the light forwards, and a side marker will collect and disperse the light to as much area as possible. Because the housing can modify the light path of the bulb, the same bulb can look completely different in two different housings.
Most older LEDs have high lux in one direction, as the light is focused, but they dont "fill up" the housing. Im sure weve all seen poorly-designed LED bulbs on the road, where you can see high lux, but low total lumens. Remember, just because a bulb "looks bright" does not mean it will perform better.
Sometimes high lux is good: you might see us refer to an LED bulb with an integrated focusing lens as "high-lux," which might be great for backup light applications, where you just want light directed behind your vehicle. However, for most replacement lights, they should evenly distribute the light, just like the factory incandescent. That way, the light housing can do its job and distribute the total light in the way it is designed. High lux is not always beneficial, but its always best to have as many lumens as possible!
Since Diode Dynamics products are designed to replace bulbs in a variety of manufacturer housings, Diode Dynamics only provide lumen measurements for company products, to give customers the best idea of the total light output. Company have a scientific integrating sphere to provide accurate measurements to our customers.
LEDs are a type of semiconductor diode. (Now you know the secret of where our name comes from!) This means they use semiconductor materials to allow electrons to pass through a p-n junction. When electrons of the n-type semiconductor fill the holes of the p-type semiconductor, energy is released as photons of light.
There must be a higher voltage potential on the p-side of the LED than the n-side for this atomic interaction to work, which is why all LEDs are polar, meaning they have specific polarity. If you see a "non-polarity LED bulb," the power controller that is built into the bulb is non-polarity, not the individual LED chips themselves.
Once the power is in the correct direction to flow through the LED, the brightness is determined by the current or the speed of the flow of power. The more electrons filling holes, the more photons released, and the higher the brightness output. Of course, LEDs can only withstand a maximum current and voltage before they "blow," so it is important to carefully control this through the correct supply of power.
Since automotive power is 12V, and LEDs generally run best on 2-4V, depending on color, you must use resistors or other components to drop the voltage to a level the LED can work with. This is why you cannot simply plug a basic LED directly into your socket, or connect it to a 9V battery. The manufacturer will determine what the nominal (normal) voltage is to run a specific LED, known as the "forward voltage." For example, a blue LED might be rated as 3.0-3.2V. Adjusting the voltage lower or higher will change the brightness, but only because it also changes the current- higher voltage means the current will increase in an LED.
After ensuring that you have the correct voltage available to the LED, the next step is determining current. This is measured in amperes or amps, but since its such a small amount of current, LEDs will be rated in milliamps (mA). There are 1000 milliamps in an amp. The more current, the brighter the LED, but there is always a maximum "running" or "constant" current, which is the max you should run the LED at, and usually there is a max "peak" current, which is the highest current the LED can withstand before completely failing.
As LEDs have evolved, they have generally required higher tolerances in terms of how much current they require and can handle. The oldest LEDs had a large range of current where they would light up and could withstand swings in current without too much of a detrimental effect. The newest LEDs can run on much higher current, to generate a much greater amount of light, but cannot handle such drastic swings while they are running, and will fail if they are put under too much stress. For this reason, it is critical to provide the correct current and voltage to LEDs, especially the newest, high-power ones.
The voltages and currents of different LEDs will vary, so to directly compare LEDs, the measure of total power consumed is also provided by the manufacturer. Power is calculated as (Voltage x Current), so an LED that is running on 20mA (.02A) and 3V would be consuming 0.06W of power.
To compare this to an incandescent bulb, though, you need to look at the total power consumed by a full LED bulb. As you mentioned, the whole LED bulb includes other components to regulate the voltage to the LEDs and might have more than one LED. If you have three LEDs running on 20mA each, you would need to supply 60mA total, and drop the voltage from 12V, so the whole bulb would consume the power of (12V x 60mA) = .72W. As you can see, a lot of power is consumed in dropping the voltage down, and you need more power to run more LEDs. Still, this example of a 60mA bulb is actually realistic for a standard 194-bulb replacement. The incandescent 194 bulb consumes 5W of power!
When you talk about efficiency, you refer to the amount of light generated for each watt of power consumed. The device will convert the power to heat and light. In the above example, if the total output of the LED and the incandescent bulb is 50 lumens, you could say that the LED has an efficiency of 50/.72 or about 70 lumens per watt. The incandescent bulb, on the other hand, will have an efficiency of 50/5 = only 10 lumens/watt! The LED is much more efficient at converting power to light.
LEDs also "run cooler" because they are more efficient- they dont convert as much of the power to heat as incandescent bulbs do. LEDs still convert power to heat, though- and some LEDs will get very hot! Specifically, in high-power LEDs, heat becomes a big problem. You must keep the LED cool enough to keep everything running properly, and this is one of the primary reasons poorly-designed LED bulbs can fail.
As company discussed, LEDs are designed to run at a nominal (normal) voltage and current for optimal operation. Manufacturers generally state the "nominal" numbers as a perfect scenario, where you can get rid of all excess heat and there wont be any changes in power, or "spikes" that the LED has to deal with.
In automotive applications, however, LEDs have to deal with large voltage swings as the alternator keeps re-charging the battery (only 1V change is considered a huge spike for an LED) and the small size of automotive bulbs means that LEDs have to be packed into a small space, which means they are not going to be able to cool themselves very well- nothing like the scenario in which the manufacturer "rated" the LEDs.
Therefore, when designing bulbs for automotive use, designers configure LED bulbs so that each LED on the bulb will run at a specifically-calculated voltage and current. By lowering the power supplied to an LED, you can get a longer life out of an LED, and it will not get as hot, but it wont be quite as bright. You can also ensure the LED wont go out if the voltage suddenly rises to 14V for a few seconds, for example.
Most designers still use the nominal ratings of each individual LED chip to describe the whole bulb, especially in high-power bulbs. For example, an 80W bulb might use 16 individual 5W-rated LEDs, so the designer will call it an "80W bulb." However, the LEDs are not going to actually consume 80W of power. Instead, the LEDs are running at a much lower actual power, in order to manage the heat and prevent them from failing prematurely. This might be called "Actual Power Consumption" or "Real Power." The Real Power consumed by the whole bulb may only be about .5 amps. Automotive LEDs are designed to run at much lower than their "full potential," in order to improve reliability.
When purchasing LED bulbs, the "80W" should only be considered the name of the bulb, not a description of its electrical properties, or even how bright it is! Yes, an "80W" bulb is probably going to be brighter than a "10W" bulb, but the total brightness all depends on how the bulb is designed. How much power is actually being used by the LEDs on that bulb? An "80W" bulb from one supplier maybe half the brightness as an "80W" bulb from another supplier. Make sure you compare the Real Power, or better yet, just find an actual lumen measurement to determine total brightness.
Watch out! Many suppliers will take the inaccurate "80W" power rating, described in the previous section, and will just assume an efficiency for that bulb depending on the type of LED. For example, they might say, "high-power LED bulbs usually emit about 10 lumens per watt, so this bulb will be about 800 lumens!" This is a complete guess and is likely completely inaccurate.
Why do they do this? It is quite expensive to test actual lumen outputs- integrating spheres can cost up to $100,000- but suppliers know it is a great way to compare bulbs, so they will "calculate" or "approximate" the lumen output for you. Sneaky, huh? If you see what seems like a completely arbitrary lumen rating, such as "1200 lumens," it probably is just that- a completely inaccurate guess.
Make sure your supplier provides "Measured Lumens," not "Calculated," "Estimated," or "Approximate." If it doesnt say "measured," its probably not accurate! Stay away from any dishonest companies that offer "calculated lumens" at all costs!
High-intensity discharge (HID) headlamps produce light with an electric arc rather than a glowing filament as you might find in a standard halogen bulb. The light itself comes from an arc of electricity, facilitated by metallic salts that are vaporized within the arc chamber. To start the bulb, an ignitor provides a high-voltage pulse to the bulb, which creates a spark, ionizing xenon gas in the bulb, creating a conducting tunnel between the tungsten electrodes at the top and bottom of the glass tube. Electrical resistance is reduced within the tube and the current flow between electrodes. As the bulb warms up, the salts continue to vaporize, further lowering resistance between the electrodes. The electronic ballast, which controls the power supply, senses the drop in resistance and adjusts to provide a continuous current to the bulb. After the bulb is fully "warmed up," the arc has attained stability, and the luminous efficacy has attained its nominal working value. The ballast then continues to supply stable electrical power to the bulb, to provide steady, bright light.
Halogen bulbs usually burn out after about 400 hours, while HID bulbs can last for 2500 hours or more. The first HID bulbs operated on a direct current (DC), but in DC, one electrode is constantly being hit with high-speed ions, since the power flows in only one direction. Over time, this erodes the electrode, resulting in a short bulb life. You might see some HID conversion kits available in DC configuration, but they are unreliable compared to the far-superior alternating current (AC) HID systems. All OEM HIDs use AC, and Diode Dynamics only provides AC components. In AC, the heat is shared between two electrodes, significantly increasing the life of the bulb and overall performance.
Size/Fitment. HID bulbs are rebased to halogen-size bulb mounts, for retrofit application in halogen headlight assemblies. In purchasing HIDs, it is crucial to select the required size for your application. Diode Dynamics maintains vehicle-specific listings to assist in this process. If the bulb does not fit properly in the housing, the light output will be compromised. This goes for any application, whether youre upgrading your factory halogen headlights with the HID Conversion Kit, or replacing your OEM HIDs. The distance of the arc-capsule in the bulb relative to the bulb base is extremely important. If the bulb is not fully seated in the back of your projector, the reflectivity of the headlight will be off, and the output will suffer.
Alignment. In addition to the fitment of the base of the bulb, it is also extremely important for the glass tube of the bulb, which contains the light source, to be aligned correctly, fully straight on the base. If the capsule is even slightly tilted, the output will be affected. It is important to make sure you purchase a bulb that is supported at the base by either a ceramic piece or metal frame, not simply a plastic piece, which can warp due to heat over time and create a misalignment. Diode Dynamics HID Bulbs are individually laser-aligned as part of the manufacturing quality control process and use a ceramic base to ensure perfect alignment. By purchasing a set of bulbs constructed at the highest quality, you will achieve better alignment, which allows for a tighter beam pattern, reducing hotspots and produce cleaner output.
Color. Color in lighting is described in Kelvin, or temperature of light. You may have seen a "3500K" rating on interior lights for your house. In HID bulbs, the halide salts determine the color of light. The bulb color or temperature is achieved by the blend of salts within the capsule, which consists mainly of scandium iodide and sodium iodide. With higher-temperature bulbs, more indium iodide is used to achieve the color. Around 23kV of power is required to start the arc across the bulb. At first, a slight blue color can be seen, which is formed from the low-temperature emission around the two electrodes. The temperature of the arc chamber rises as the arc continues, and vaporizes the salts in the capsule. The vaporized salts are ionized into a plasma, which emits the light and lowers the voltage. When checking a bulb for quality, you should note a generous portion of salts resting in the capsule- little or no visible salts is an indication of poor quality, as the salts are one of the more expensive parts of a bulb, and cheaper manufacturers will cut costs here.
As HID bulbs age, the Kelvin color temperature rises, or becomes "cooler," causing the output color to be more of a bluish-white. This is called a color-shifting. If you see a car with five-year-old 4300K HID bulbs, they would probably look like they were running 6000K bulbs. This is because over time, the electrodes deform, and the blue glowing of the plasma region around the larger surface area of these deformed electrodes contributes a cooler color to the total output.
UV Output. The arc of light from an HID bulb can give off some harmful UV rays, so it is standard practice for a glass shell to be placed around the capsule to soften the UV output. This is why there are actually two glass tubes in each bulb.
Wattage. The power provided to an HID bulb will determine the total light output and will also affect the color output. As power increases, light output increases and the color becomes more "washed out," becoming more white. The two most common power levels of HID bulbs are 35-watt and 55-watt. In fact, the bulbs work in exactly the same way, but since higher power washes out color, the 55W 6000K will be designed with "cooler" salt composition than a 35W 6000K bulb, so that when you fire them up, theyll both appear 6000K, even though one is driven by 35W and one is driven by 55W. Most bulbs on the market are 35W, and OEM HID is always 35W, but 55W kits have been promoted as an up-sell by many companies, although they cost the same to produce. At Diode Dynamics, only offer 35W bulbs and components, as 55W bulbs produce an excessive amount of heat, which can damage the headlight or foglight housing, and have a much shorter lifespan. Please be sure to read the section on ballasts in order to see more reasons 55W isnt really worth it!
Warranty: Although HID Bulbs last longer than halogen bulbs, they will eventually burn out. However, defects in electronics manufacturing do occur, so when purchasing your bulbs and ballasts, make sure that the manufacturer or distributor offers a good warranty and replacement policy in case something happens to the bulbs. At Diode Dynamics, comapny provide a full 3-year warranty on all HID bulbs and ballasts.
A ballast is a device that controls power output in a variable manner. They are found in most types of arc lighting, such as commercial florescent lights, and of course, in automotive HIDs. The ballast is composed of an electrical circuit that can be designed to fit into any shape of housing, which is usually aluminum. The circuitry is inside the housing, and it should be fully sealed in a process known as potting, to make the ballast completely waterproof. The quality of the ballast can be determined by the quality of electrical components on the circuit, quality of circuit construction, and the amount of watertight sealant used inside the housing.
The main role of the ballast is to control power supply. After igniting the bulb, the power is carefully controlled as the bulb "warms up" and resistance decreases. This is what determines how quickly the bulb warms up: too much power delivery will create premature failure, too little power will mean a long warmup time. In a digital ballast, the controller chip analyzes the changing resistance continually and varies the power output in order to warm the bulb up more quickly and safely. The best ballasts on the market use an application-specific integrated circuit (ASIC) for this, which is designed specifically for use in HID ballasts. Most generic aftermarket ballasts still work well with generic controller chips, but the best performance is only provided by an ASIC chip. ASIC chips can be found in all OEM ballasts, as well as Diode Dynamics premium aftermarket ballasts.
The main circuitry controls the power output to the bulb, but to get things started, the bulb requires a large pulse of power, usually at least 23kV, which is provided by a component called an ignitor. Older non-digital aftermarket ballasts have the igniter integrated into the ballast housing, along with the ballast circuitry. In newer slim ballasts, the ignitor is moved outside of the main housing to save space.
Typically ballasts have anywhere from a 0.1% to 20% failure rate and vary immensely in quality. HYLUX is a common manufacturer for both aftermarket and OEM ballasts. The HYLUX ballasts have less than a 0.2% failure rate.
3000K: is lowest temperature, and has a pure yellow output, which is great for use in fog lights or for a unique look.
4300K: is a pure white output, and is used in all factory HIDs. It will not have any blue tint, just a natural white color.
6000K: is most popular color, which produces an ice white color. It has a slight hint of blue and matches best with our LED bulbs.
8000K: is highest temperature, which produces an ice blue color.