- Fluorescent light source
In a fluorescent light source, the electrical current excites mercury vapor, which produces ultraviolet radiation, and excites the phosphors to produce visible light. It is also called a gas discharge lamp. Fluorescent lamps also require ballasts to function properly. Fluorescent lamps are mostly made in straight tube type, but for more energy saving and environmental protection, compact fluorescent lamps (CFL) can also be made to replace incandescent lamps. CFLs with screw bases type E27 can be mounted on the base without any changes and are a direct replacement for incandescent lamps (see Figure 1).
Compared with incandescent lamps, fluorescent lamps increase the ratio of input electrical energy into visible light output. Compared with the theoretical upper limit of luminous efficacy of incandescent lamps of 521m/W, fluorescent lamps can reach 1001m/W. So for a certain light output (in Im), a fluorescent lamp will generate less heat and consume less electricity. Its 10000h service life and high power efficiency make it more economical.
However, fluorescent lamps also have many disadvantages. The first is its safety, because the fluorescent lamp’s glass is filled with mercury, which is very fragile. Mercury therefore needs to be treated and recycled after use. Fluorescent lamps also emit certain ultraviolet (UV) rays, which can cause harm to the human body and affect the color of artwork or exhibits. Also, if it is switched on and off frequently, it will age rapidly because the electron-emitting surface of the cathode is depleted each time the fluorescent lamp is operated.
The efficacy of fluorescent lamps decreases with increasing temperature, and they work best at room temperature. However, if it is in a very low temperature environment, there will be many difficulties in its operation, so harsh climatic conditions will limit the application of fluorescent lamps, such as fluorescent lamps in extremely cold areas will not be suitable for road lighting.
- High-intensity discharge lamps
High-intensity discharge (HID) lamps are typically used for outdoor lighting or for large-area indoor lighting. It exhibits the highest efficiency and service life. It works by forming an arc at a high enough voltage and then producing a strong light. The most common HID lamps are the oldest and least efficient mercury vapor lamps, high pressure sodium lamps and metal halide lamps. Most HID lamps produce large amounts of ultraviolet radiation that are harmful to humans and animals.
- Low pressure sodium lamps
Low-pressure sodium lamps are similar in principle to fluorescent lamps. It is a very efficient light source with a long service life, but has poor color rendering. Therefore, low pressure sodium lamps are usually used in occasions where the color requirements are not high, and the objects presented are all yellow or gray. When comparing the cost of various light sources, we should not be limited to the initial cost, but also consider efficiency, lifetime and environmental impact. The cost of incandescent lamps is attractive compared to fluorescent or LED lamps. To be precise, when comparing the operating costs of incandescent lamps with other light sources, other parameters such as luminous efficacy (In/W), lighting requirements as well as space constraints, aging effects and service life must be taken into account, and of course health and environmental protection question.
The challenges encountered in the development of LEDs are as follows:
1) Select appropriate semiconductor materials to achieve efficient carrier radiative recombination and appropriate emission wavelengths.
2) Higher light extraction rate: overcome total reflection and reabsorption.
3) Appropriate packaging form: high light extraction rate, specific beam shape, good heat dissipation, high mechanical strength, long service life and stable chromaticity The development of LEDs is far from over, and the industry is actively exploring How to improve the LED lighting efficiency, color rendering, service life and how to reduce the cost, so that it can completely replace the traditional lighting system. The next few years will witness a higher market share of LEDs due to factors such as falling prices, higher energy conversion efficiency, better light and color quality, and more environmental protection.
Read more: What is the current energy scenario?