Lighting Comparison: LED versus HID Lights

Ever wonder what’s better: High Intensity Discharge (HID) lights or Light Emitting Diodes (led lighting)? Well here’s a head-to-head comparison of the two followed by an in-depth discussion of each technology in turn.

High Intensity Discharge (HID) What is a High Intensity Discharge (HID) Light:

High Intensity Discharge is an overarching term for a gas-discharge light. They are the oldest type of electrical light Among the common types of HID lights are mercury vapor, low and high pressure sodium and metal halide lamps. Other less common variants include ceramic metal halide and xenon short-arc lamps. HID lamps produce light by sending an electrical charge or “arc” between two tungsten electrical conductors (electrodes) and through an ionized gas (also known as “plasma”) which is housed inside the bulb. HID lights require ignition which is typically provided by a voltage pulse or a third electrode (an additional metal part) internal to the bulb. Once lit the electrical arc begins to evaporate the metal salts inside the bulb which significantly increases the luminous power of the bulb while simultaneously improving lighting efficiency. HID lighting requires a “warm-up” period because the lighting intensity is dependent on and changes as the material inside the bulb is evaporated into plasma. Additionally, as the light heats up it requires additional voltage to operate. Voltage requirements in HID bulbs are balanced by an electrical ballast (essentially a device that limits electrical current to that required to operate the lamp). As the HID light ages, more and more voltage is required to produce the same amount of light until eventually the voltage exceeds the fixed resistance provided by the ballast and the light goes out (fails). HID lights become less and less efficient over time because they must use more and more voltage to produce the same lumen output as the light degrades.

What is the Upside to HID Lights HID technology has been around for several centuries and is typically used when high intensity, high efficiency, or lighting over a vast area is required. New HID lamps produce more visible light per unit of energy than both incandescent and fluorescent lamps because a smaller proportion of the energy emitted is in the infrared spectrum (i.e. more is in the visible light spectrum). Generally speaking they are efficient and produce a high quality light.

What are the Major Deficiencies in HID Lights: Amongst the deficiencies in HID lighting are the following:

A portion (roughly 30%) of the energy emitted by HID lights is infrared (which in terms of lighting output means it’s entirely wasted energy). Although this figure is worse for older variants of the technology and better for new HID bulbs, it’s a relevant inefficiency in either case. Of note, both incandescent and fluorescent bulbs are worse than HID with respect to the percentage of radiation that is infrared vice visible light. HID lumen output can significantly deteriorate as the bulb ages. Some HID bulbs produce 70% less visible light after only 10,000 hours of operation. Most HID lighting emits a significant amount of UV radiation. Due to this deficiency HID lamps require UV filters to prevent fading of dyed items exposed to their light, degradation of lamp fixture parts, or serious injury (sunburn or arc eye) to humans and animals. HID lights are omnidirectional. Omnidirectional lights produce light in 360 degrees. This is a large system inefficiency because at least half of the light needs to be reflected and redirected to the desired area being illuminated. The need for reflection and redirection of light means that the output is much less efficient for omnidirectional lights due to losses than it would be for the same light if it were directional by its nature. It also means that more accessory parts are required in the light fixture itself in order to reflect or focus the luminous output of the bulb (thus increasing unit costs). What are the Minor Deficiencies in HID Lights: Amongst the minor deficiencies in HID lighting are the following:

HID lights have a warm-up period . Once the arc is ignited it melts and evaporates metal salts internal to the device. The light doesn’t arrive at full power until the salts are fully evaporated into plasma. Due to the fact that higher voltage is required as the light heats up and progressively more so as the light ages, HID lights display discoloration or “fading” over time. Normal operations might show a shift towards blue or violet light (as extra voltage is applied when the light heats up), but towards the end of the bulb’s life (as more and more voltage is required in a fully warmed up condition) it might look as though it is only producing blue and/or violet light. Because HID degrades over time (both in efficiency and in light quality) it is often recommended that bulbs be changed out prior to their advertised useful life. This generally increases costs for the end-user. HID lights , similar to fluorescent lights, require a ballast to stabilize the light. In the event that there is a minor flaw in the ballast the light may produce an audible hum or buzz. HID lights contain toxic material internally . This is particularly true with Mercury-Vapor Lamps which internally contain a significant amount (up to 50 mg) of toxic mercury vapor. As a consequence of contaminants like mercury, HID lights require special waste disposal procedures when broken or at the end of their useful life. Where Is HID Commonly Used: Common applications for HID lighting include sports stadiums or gymnasiums, warehouses, large public areas (which require powerful, efficient lights over a large area), road lighting (which frequently utilize low and high pressure sodium lights), and parking lots. For an interesting take on the history of street lighting in the United States read here . HID is also used in automotive lighting and indoor gardening.

LED: What is a Light Emitting Diode (LED): LED stands for Light Emitting Diode. A diode is an electrical device or component with two electrodes (an anode and a cathode) through which electricity flows - characteristically in only one direction (in through the anode and out through the cathode). Diodes are generally made from semiconductive materials such as silicon or selenium - solid state substances that conduct electricity in some circumstances and not in others (e.g. at certain voltages, current levels, or light intensities). When current passes through the semiconductor material the device emits visible light. It is very much the opposite of a photovoltaic cell (a device that converts visible light into electrical current).

If you’re interested in the technical details of how an LED works you can read more about it here .

What’s The Major Upside to LED Lights: There are four major advantages to LED lighting:

LEDs have an extremely long lifespan relative to every other lighting technology (including HID). New LEDs can last 100,000 hours or more. The typical lifespan for an HID bulb, by comparison, is 10-25% as long at best (10,000 - 25,000 hours). LEDs are extremely energy efficient relative to every other commercially available lighting technology. There are several reasons for this to include the fact they waste very little energy in the form of infrared radiation (much different than most conventional lights to include HID), and they emit light directionally (over 180 degrees versus 360 degrees which means there are far fewer losses from the need to redirect or reflect light). Very high light quality. Very low maintenance costs and hassle. What Are The Minor Upsides to LED Lights: In addition to the major advantages, LED lights also offer several smaller perks. These include the following:

Accessories: LEDs require far fewer accessory lamp parts. Color: LEDs can be designed to generate the entire spectrum of visible light colors without having to use the traditional color filters required by traditional lighting solutions. Directional: LEDs are naturally directional (they emit light for 180 degrees by default). Size: LEDs can be much smaller than other lights. Warm-Up: LEDs have faster switching (no warm-up or cool-down period). What’s The Downside to LED Lights: Considering the upside you might think that LED lights are a no-brainer. While this is increasingly becoming the case, there are still a few tradeoffs that need to be made when you choose LED:

In particular, LED lights are relatively expensive. The up-front costs of an LED lighting project are typically greater than most of the alternatives. This is by far the biggest downside that needs to be considered. That said, the price of LEDs are rapidly decreasing and as they continue to be adopted en masse the price will continue to drop.

Where is LED Commonly Used: The first practical use of LEDs was in circuit boards for computers. Since then they have gradually expanded their applications to include traffic lights, lighted signs, and more recently, indoor and outdoor lighting. Much like HID, modern LED lights are a wonderful solution for gymnasiums, warehouses, large public areas (which require powerful, efficient lights over a large area), road lighting (which offer significant color advantages over low and high pressure sodium lights), and parking lots. For an interesting take on the history of street lighting in the United States read here .

Further Qualitative Comparison: What’s The Difference Between HID and LED Lights: The two different technologies are entirely different methods of producing light. HID bulbs contain inert gas within the glass casing while LEDs are a solid state technology. HIDs emit a lot of heat and a large portion of their emissions fall in both the IR and UV spectrum. LEDs emit across a small portion of the visible light spectrum and don’t waste energy by producing waste heat or non-visible electromagnetic radiation. There is such a thing as an IRED (infrared emitting diode) which is specifically designed to emit infrared energy.

Why would LEDs put HID lights out of business? Source vs system efficiency is the main reason. So what is source efficiency versus system efficiency? HID lights are very efficient when measured at the source (lumens/watt). This measurement, however, does not take into account the amount of light that actually hits the target area (system efficiency). System efficiency is affected by a myriad of factors that include losses due to trapped light, protective covers or lenses, non-standard operating temperatures, and losses due to power conversion. System efficiency for HID l ights is generally only 25% of the source efficiency, as compared to LED lights (whose system efficiency is closer to 50% of the source efficiency). The result is a much more effective light in the case of LEDs.

Additionally, HIDs bring with them a myriad of potential problems. Amongst the major items include repetitive maintenance and replacement costs both in parts and labor (HIDs have a much shorter lifespan than LEDs), potentially hazardous waste (internal mercury) and dangerous emissions (UV) in the event that the bulb is broken or the casing experiences some type of failure, and small things like required warm-up times, inability to effectively dim, and typically shorter warranty coverage.

The major advantage of HIDs is that in some cases (particularly with low and high pressure sodium bulbs) the initial purchase price will be much lower. Typically LEDs make up for their higher purchase price with reduced maintenance and energy costs across a specific payback period. Curious about payback period and return on investment analysis? Try our ROI calculator . Additionally, another specific tradeoff with LPS and HPS bulbs in particular is that they are monochromatic yellow with an abysmal Color Rendering Index (in other words, everything illuminated by them shows up yellow. You literally can’t see color when using LPS or HPS lighting).

LEDs are a simple invention with huge potential to change the lighting industry for the better. While the technology has been gradually adopted, it is advancing rapidly and already beats the competition in many if not most applications.

HID vs LED Comparison Correlated Color Temperature LED is available in a wide range of color temperatures that generally span from 2200K-6000K (ranging from yellow to light blue). LEDs generally have better color temperature options than HID.

HID lamp color temperatures are determined by the materials used to generate the light. High Pressure Sodium, Metal Halide, and Mercury Vapor all utilize different chemical compositions to generate light and have specific color temperatures associated with the composition within their bulb.

WINNER: LED

CRI CRI for LED is highly dependent on the particular light in question. That said, a very broad spectrum of CRI values is available ranging generally from 65-95.

Typical CRI values range from extremely low in the case of low and high pressure sodium lamps (0-25) to moderate in the case of metal halide lamps (60). Some HID lights may reach CRI as high as the mid 90s.

WINNER: LED

Cycling (Turning On/Off) LEDs are an ideal light for purposely turning on and off because they respond rather instantaneously (there is no warm up or cool down period). They produce steady light without flicker.

HID lights require a noticeable warm up period that ranges from half a second in the case of car lights to several minutes in the case of stadium lighting. They may also flicker or cycle on and off as the bulb reaches the end of its useful life.

WINNER: LED

Dimming LEDs are very easy to dim. They do this by either lowering the forward current or modulating the pulse duration.

HID lights can be manually dimmed through the use of different electric or magnetic ballast but the process changes the voltage input to the light and can consequently alter the light characteristics. In some cases (particularly with older HID bulbs) dimming can cause the light to prematurely expire. Otherwise HID bulbs cannot be dimmed.

WINNER: LED

Directionality LEDs emit light for 180 degrees.

HID is omnidirectional meaning it emits light for 360 degrees.

WINNER: LED

Efficiency LEDs are very efficient relative to every lighting type on the market. Typical source efficiency ranges 37 and 120 lumens/watt. Where LEDs really shine, however, is in their system efficiency (the amount of light that actually reaches the target area after all losses are accounted for). Most values for LED system efficiency fall above 50 lumens/watt.

HIDs are very efficient compared to CFL and incandescent lights (120 lumens/watt source efficiency). They lose out to LEDs principally because their system efficiency is much lower (&lt;30 lumens/watt) due to all of the losses associated with omnidirectional light output and the need to redirect it to a desired area. By far the most efficient HID variant is the High Pressure Sodium lamp whose source efficiency can range from 100-190 lumens/watt.

WINNER: LED

Efficiency Droop LED efficiency drops as current increases. Heat output also increases with additional current which decreases the lifetime of the device. The overall performance drop is relatively low, however, when compared to HID.

HID lights also experience efficiency losses as the device ages and additional current is required to achieve the same lighting output. Efficiency losses are greater and the degradation time shorter in the case of HID.

WINNER: - (Note: Recent advances in LEDs will likely improve their droop qualities)

Emissions (In Visible Spectrum) LEDs produce a very narrow spectrum of visible light without the losses to irrelevant radiation types (IR or UV) associated with conventional lighting.

HID lights produce relevant amounts of both IR and UV radiation.

WINNER: LED

Ultraviolet &amp; Infrared LEDs - NONE

Roughly 30% of the emissions from HID lights are in the infrared spectrum (thus completely useless for the purposes of regular illumination)

HID emits a lot of UV radiation. So much so that special filters are required to prevent fading of dyed surfaces exposed to HID light, serious damage to light fixtures, and/or even serious harm to human beings and animals (e.g. serious sunburn or arc eye).

WINNER: LED

Failure Characteristics LEDs fail by dimming gradually over time.

HIDs exhibit an end-of-life phenomenon known as cycling where the lamp goes on and off without human input prior to eventually failing entirely.

WINNER: LED

Foot Candles Foot candle is a measure that describes the amount of light reaching a specified surface area as opposed to the total amount of light coming from a source (luminous flux).

LEDs are very efficient relative to every lighting type on the market. Typical source efficiency ranges 37 and 120 lumens/watt. Where LEDs really shine, however, is in their system efficiency (the amount of light that actually reaches the target area after all losses are accounted for). Most values for LED system efficiency fall above 50 lumens/watt.

HIDs are very efficient compared to CFL and incandescent lights (120 lumens/watt source efficiency). They lose out to LEDs principally because their system efficiency is much lower (&lt;30 lumens/watt) due to all of the losses associated with omnidirectional light output and the need to redirect it to a desired area. By far the most efficient HID variant is the High Pressure Sodium lamp whose source efficiency can range from 100-190 lumens/watt.

WINNER: LED

Heat Emissions LEDs emit very little forward heat. The only real potential downside to this is when LEDs are used for outdoor lighting in wintery conditions. Snow falling on traditional lights like HID will melt when it comes into contact with the light. This is usually overcome with LEDs by covering the light with a visor or facing the light downward towards the ground.

HIDs emit a lot of heat. In some circumstances this could be beneficial, however, it is a generally a bad thing as heat losses represent energy inefficiencies. The ultimate purpose of the device is to emit light, not heat.

WINNER: LED

Life Span LEDs last longer than any light source commercially available on the market. Lifespans are variable but typical values range from 25,000 hours to 200,000 hours or more before a lamp or fixture requires replacement.

HID lights have good lifespan relative to some bulbs but not compared to LED. Typical lifespan values range from 6,000 hours to 24,000 hours before a bulb requires replacement. Note: sometimes HID lights need to be changed out before the end of their useful life to preempt serious degradation effects like color changes or cycling.

WINNER: LED

Lifetime Cost LED lighting has relatively high initial costs and low lifetime costs. The technology pays the investor back over time (the payback period). The major payback comes primarily from reduced maintenance costs over time (dependent on labor costs) and secondarily from energy efficiency improvements (dependent on electricity costs).

HID is relatively cheap to purchase but it is relatively expensive to maintain. HID bulbs will likely need to be purchased several times and the associated labor costs will need to be paid in order to attain the equivalent lifespan of a single LED light.

WINNER: LED

Maintenance Costs LED has virtually zero maintenance costs and the frequency with which bulbs have to be changed out is by far the best on the market.

HID bulbs require regular relamping and ballast replacement in addition to the labor cost to monitor and replace aging or expired components.

WINNER: LED

Upfront Costs LED light costs are high but variable depending on the specifications. The typical 100W-equivalent LED light costs somewhere between $10 and $20.

HID bulb costs depend on the specific type of HID light. HPS lights are relatively cheap ($5-$10 for a 100W bulb) while a 100W mercury vapor light typically costs around $15. A 100W Metal Halide light costs somewhere between $10 and $30 per bulb depending on the specifications.

WINNER: HID

Shock Resistance LEDs are solid state lights (SSLs) that are difficult to damage with physical shocks.

HID bulbs are relatively fragile. Perhaps more importantly, broken HID bulbs require special handling and disposal due to hazardous materials like mercury inside of many lights.

WINNER: LED

Size LEDs can be extremely small (less than 2mm in some cases) and they can be scaled to a much larger size. All in all this makes the applications in which LEDs can be used extremely diverse.

HID bulbs can be small but typically aren’t produced below roughly a centimeter in width. The size of the lamps is limited by the wattage and light output required for a given application.

WINNER: LED

Cold Tolerance LEDs - Minus 40 Degrees Celsius (and they will turn on instantaneously).

HID - Minus 40 degrees Celsius

WINNER: LED

Heat Tolerance 100 Degrees Celsius. LEDs are fine for all normal operating temperatures both indoors and outdoors. They do, however, show degraded performance at significantly high temperatures and they require significant heat sinking, especially when in proximity to other sensitive components.

We couldn’t find any objective data on HID bulb performance in high temperature situations. If you have any information please contact us.

WINNER: -

Warm Up Time LEDs have virtually no warm-up time. They reach maximum brightness near instantaneously.

HIDs require a noticeable warm-up time that varies depending on the light. HID lights in automobiles take roughly half a second to power up while HID lights for sporting stadiums might take several minutes to arrive at maximum brightness.

WINNER: LED

Warranty LEDs - Often 5-10 years

Metal Halide - typically 1-2 years

WINNER: LED

Winter Weather Conditions LED’s ability to withstand colder temperatures without a compromise in lighting performance is an advantage in winter weather conditions, particularly for outdoor lighting application. Since the light generated from LEDs occurs from electroluminescence, the colder temperatures do not result in an extended “warm-up time” and as a result the light generation is almost instantaneous. LEDs also produce significantly less forward heat then HID lighting. This is typically a positive, however, for the unique case of application with traffic lights, there is a small potential that snow can accumulate on the bulbs. In reality, however, this is generally not an issue due to the use of visors and/or proper orientation of the light within a fixture that shields it from the elements.

HID Lamps require that the materials within the lamp reach a certain temperature (often very high) in order for the actual light to be generated. In colder temperatures it can take longer for the lamps to reach those optimal temperatures, resulting in longer “warm-up” times and on certain occasions a shortened operational life time. However, since HID bulbs produce significant forward heat, they have the advantage of melting snow that may build up in horizontal lighting applications by virtue of being turned on.

WINNER: LED

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