MainPage:Nuclear:Summer2014:LEDSpectrum

Abstract

Light-Emitting Diodes have a multitude of uses due to their increasing efficiency, long life, reliability, durability, and practical size. As the uses for LEDs widen, there is a greater need to precisely know their optical characteristics. Therefore, this project aims to determine the spectrum of Light-Emitting Diodes and the relationship between wavelength and light intensity. To record the spectrums of the various LEDs present in the lab, a spectrometer must be constructed. A power source will be attached to the LED so that it may convert electrical energy into light. After the light is converted into a more precise beam by a collimator, it will be separated into various wavelengths (or colors) by the diffraction grating. A slit will then limit which wavelength of light may be detected and amplified so that the voltage and thus intensity of the light may be recorded.

Light-Emitting Diodes

Background

Light-Emitting Diodes, or LEDs, were first developed by Nick Holonyak Jr. in 1962. LEDs are a type of semiconductors that convert electrical energy into light. LEDs are relatively efficient and have surpassed incandescents and will soon surpass fluorescents, due to the creation the high-power white LED. LEDs are durable and reliable. While incandescent bulbs convert only about 5% of their power into light, LEDs convert about 15 to 20% pf their power into light, making them much more efficient. Since we believe LEDs will become 10 time more efficient than incandescent bulbs, they promise to provide a source for general lighting in the near future. If LEDs are to be used on such a broad scale in the future, it is vital that more information on the optical characteristics be recorded.

The first high-brightness blue LED was demonstrated rather recently, simply in 1994, and led to the creation of the white LED. Development in the creation of LEDs causes efficiency and light output to double about every three years since the 1960s. Plus, it has led to advancements in other semiconductor technologies and optics. The popularity of LEDs is also increasing due to new methods being discovered that would reduce the production costs by tremendous amounts.

How they Work

An LED is a semiconductor with a p-n junction. Current flows from the anode or p-side of the diode to the cathode or n-side. When an electron and a hole meet, the electron travels to a lower energy level and releases a photon and thus emitting light. The color or wavelength of the light emitted varies based on theband gap energy of the material. LEDs are created of material with a direct band gap and thus the energies correspond to near-infrared, visible, or near-ultraviolet light.

Spectrometers

Spectrometers are instruments used to measure properties of light, by separating the light into its spectral components, and then measuring light intensity or wavelength. The basic components of a spectrometer, also known as a spectrophotometer, are a light source, a collimator, a diffraction grating, a slit, and a detector. Some spectrometers have computers or other devices which analyze the data from the detector and determine radiation intensity as a function of wavelength.

First, the light enters the collimator, which focuses and narrows the light rays by making them parallel to each other. The beam of light then hits a diffraction grating, which diffracts the light into different beams, depending on the wavelengths of the light. The slit in the spectrometer allows only one specific wavelength through to the detector. The detector determines the voltage of the wave, which is amplified with an op amp and displayed on the voltmeter.

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Sources

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