What Is A LED? How are LEDs Better?
Led lighting (a light-emitting-diode) advantages and disadvantages.
A light emitting diode is a two-lead semiconductor light source. The effect when this happens is called electroluminescence the color of the light determined by the energy band gap of the 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 LED’s 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.
LED’s have many advantages over incandescent light sources.
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.
LEDs can be tiny (smaller than two mm2) and are easily attached to printed circuit boards.
Warm up time:
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.
LEDs can very quickly be dimmed either by Pulse-width modulation or lowering the forward current. This pulse-width modulation is why LED lights, in particular headlights on cars, when viewed on camera or by some people, appear to be flashing or flickering. Type of stroboscopic effect.
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.
LEDs mostly fail by dimming over time, rather than the sudden collapse of incandescent bulbs.
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 may be longer.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, is the primary factor in determining the payback period for a LED product.
LEDs, being solid state components, are difficult to damage with external shock, unlike fluorescent and incandescent bulbs, which are fragile.
The robust package of the LED can be designed 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 are 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.
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. The additional expense partially stems from the relatively low lumen output and the drive circuitry and power supplies needed.
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 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.
LEDs must have voltage beyond their threshold voltage and a current below their rating. Current and lifetime change substantially with a small change in applied voltage. They thus require a current-regulated supply (usually just a series resistor for indicator LEDs).
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, 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 distribution. 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.
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.
There is a concern that blue 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.
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.
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 low CCT LEDs).
The efficiency of LEDs decreases as the electric current increases. Heating also increases with higher currents which shorten the lifetime of the LED. These effects put practical limits on the current through a LED in high power applications.
Impact on insects:
Use in winter conditions:
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 the 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)
Light appearance, measured by correlated color temperature (CCT) on the Kelvin (K) scale, from warm to cool.
As of 2016 LED’s 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.
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