What Is A LED? How are LEDs Better?

A light-emitting diode is a two-lead semiconductor light source electroluminescence, the color of the light determined by the energy bandgap of a semiconductor.

LED’s are often small in area and integrated optical components.  Early LED’s used as indicator lamps for electronic devices. Replacing the incandescent bulbs. The radiation pattern of LED’s employed in remote controls. They applied for numeric readouts. Usually, in the form of seven digital read displays and are commonly seen on digital clocks.

LEDs have low energy consumption, longer life, improved durability, smaller size, faster switching.

Modern LEDs are available across the visible ultraviolet and infrared wavelengths, with very high brightness. The automotive industry is particularly interested in the LED lighting industry.

Recent developments in LED’s permit them in environmental and task light.

We see the integration of LEDs in every aspect of our environment: auto headlamps, traffic lights, and general lighting of our streets.

LEDs have many advantages over incandescent light sources.

Advantages

Efficiency:

LEDs emit more lumens per watt than incandescent light bulbs.^[137] The effectiveness of LED lighting fixtures is not affected by shape and size, unlike fluorescent light bulbs or tubes.

Color:

LEDs can emit light of an intended color without using any color filters as traditional lighting methods need.

Energy-efficient and can lower initial costs.

Size:

LEDs can be tiny (smaller than two mm^2[138]) and are easily attached to printed circuit boards.

Warm-up time:

LEDs light up very quickly. A typical red indicator LED will achieve full brightness in under a microsecond.^[139] LEDs used in communications devices can have even faster response times.

Cycling:

LEDs are ideal for uses subject to frequent on-off cycling, unlike incandescent and fluorescent lamps that fail faster when cycled often, or high-intensity discharge lamps (HID lamps) that require a long time before restarting.

Dimming:

LEDs can very quickly be dimmed either by Pulse-width modulation or lowering the forward current.^[140] This pulse-width modulation is why LED lights, particularly headlights on cars, when viewed on camera or by some people, appear to be flashing or flickering.  Type of stroboscopic effect.

Cool light:

In contrast to most light sources, LEDs radiate little heat in the form of IR that can cause damage to sensitive objects or fabrics. Wasted energy dispersed as heat through the base of the LED.

Slow failure:

LEDs mostly fail by dimming over time, rather than the sudden collapse of incandescent bulbs.^[65]

Lifetime:

LEDs can have a relatively long useful life. One report estimates 35,000 to 50,000 hours of useful life, though time to complete failure maybe longer.^[141]Fluorescent Lights typically are rated at about 10,000 to 15,000 hours, depending partly on the conditions of use, and incandescent light bulbs at 1,000 to 2,000 hours.

Several DOE demonstrations have shown that reduced maintenance costs from this extended lifetime, rather than energy savings, are the primary factor in determining the payback period for a LED product.^[142]

Shock resistance:

LEDs, being solid-state components, are difficult to damage with external shock, unlike fluorescent and incandescent bulbs, which are fragile.

Focus:

The design of the LED is to focus its light. Incandescent and fluorescent sources often require an external reflector to collect light and direct it efficiently. For larger LED packages, total internal reflection (TIR) lenses commonly used to the same effect.

However, when large quantities of light are needed, many light sources will deploy, which are difficult to focus or collimate towards the same target.

Disadvantages

Initial price:

LEDs are currently slightly more expensive (price per lumen) on an initial capital cost basis than other lighting technologies. As of March 2014, at least one manufacturer claims to have reached $1 per kilolumen.^[143] The additional expense partially stems from the relatively low lumen output and the drive circuitry and power supplies needed.

Temperature dependence:

LED performance largely depends on the ambient temperature of the operating environment – or thermal management properties. Overdriving a LED in high ambient temperatures may result in overheating of the LED package, eventually leading to device failure.

An adequate heat sink is needed to maintain a long life. Ruggedness is of particular importance for the automotive, medical, and military uses where devices must operate over a wide range of temperatures, which require low failure rates.

Toshiba has produced LEDs with an operating temperature range of −40 to 100 °C, which suits the LEDs for both indoor and outdoor use in applications such as lamps, ceiling lighting, street lights, and floodlights.^[103]

Voltage sensitivity:

LEDs must have voltage beyond their threshold voltage and a current below their rating. Current and lifetime changes substantially with a small change in applied voltage. They thus require a current-regulated supply (usually just a series resistor for indicator LEDs).^[144]

Color rendition:

Most cool-white LEDs have spectra that differ significantly from a black body radiator like the sun or incandescent light. The spike at 460 nm and dip at 500 nm can cause the color of objects to be perceived differently under cool-white LED illumination than sunlight or incandescent sources, due to metamerism,^[145] red surfaces being rendered particularly poorly by typical phosphor-based cool-white LEDs.

Area light source:

Single LEDs do not approximate a point source of light, giving a spherical light distribution, but rather a Lambertian delivery. So LEDs are difficult to apply for applications needing a spherical light field; however, various administrations light through the use of different optics or “lenses.” LEDs cannot provide divergence below a few degrees. In contrast, lasers can emit beams with differences of 0.2 degrees or less.^[146]

Electrical polarity:

Unlike incandescent light bulbs, which illuminate regardless of the electrical polarity, LEDs will only light with correct electrical polarity. To automatically match source polarity to LED devices, The use of rectifiers for this application.

Blue hazard:

There is a concern that the blue light emitted by LEDs. And cool-white LEDs are now capable of exceeding safe limits of the so-called blue-light hazard as defined in eye safety specifications such as ANSI/IESNA RP-27.1–05: Recommended Practice for Photobiological Safety for Lamp and Lamp Systems.^[147][148]

Light pollution:

white LEDs, especially those with high color temperature, emit much more short-wavelength light than conventional outdoor light sources such as high-pressure sodium vapor lamps, the increased blue and green sensitivity of scotopic vision means that white LEDs used in outdoor lighting cause substantially more sky glow.^{[128][149][150][151][152]}

The American Medical Association warned on the use of high blue content white LEDs in street lighting, due to their higher impact on human health and environment, compared to low blue content light sources (e.g., High-Pressure Sodium, PC amber LEDs, and small CCT LEDs).^[153]

Efficiency droop:

The efficiency of LEDs decreases as the electric current increases. Heating also increases with higher currents, which shortens the lifetime of the LED. These effects put practical limits on the current through a LED in high power applications.^{[58][60][61][154]}

Impact on insects:

LEDs are much more attractive to insects than sodium-vapor lights, so much so that there has been speculative concern about the possibility of disruption to food webs.^[155][156]

Use in winter conditions:

Since they do not give off much heat in comparison to incandescent lights, LED lights used for traffic control can have snow obscuring them, leading to accidents.^[157][158]

Today shopping for light bulbs can be confusing. In the past, we based our decision on how much energy or Watts they used. It makes better sense to buy light bulbs based on how much light they will provide.

Now choosing a light bulb in today’s technology requires attention to the lumens. A lumen is the measure of the brightness you want. You have to compare lumens instead of Watts.

Rule of thumb:

To replace a 100-watt incandescent bulb, look for a lamp that gives you about 1600 lumens.

Fewer lumens less bright, more lumens, more brilliant light.

Replace a 75W bulb with an energy-saving bulb that gives you about 1100 lumens

Replace a 60W bulb with an energy-saving bulb that gives you about 800 lumens

Replace a 40W bulb with an energy-saving bulb that gives you about 450 lumens.

WHAT SHOULD I LOOK FOR ON THE PACKAGE? THE LIGHTING FACTS LABEL

To help consumers better understand the switch from watts to lumens, the Federal Trade Commission requires a new product label for light bulbs. It helps people buy light bulbs that are right for them.

Lighting Facts label helps consumers understand what they are purchasing. The tag includes the following information:

Brightness, measured in lumensEstimated yearly energy cost (similar to the EnergyGuide label)

Lifespan

Light is measured by correlated color temperature (CCT) on the Kelvin (K) scale, from warm to cool.

As of 2016, LEDs are sturdy enough for room lighting, LED lighting remains somewhat more expensive and requires more precise heat management than compact fluorescent lamp sources with comparable output. They are, however, significantly more efficient and, arguably, have fewer environmental concerns linked to their disposal.

• https://energy.gov/https://en.wikipedia.org

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Kevin

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kevin@doledssaveenergy.com