History of Lighting

Lighting technologies up to now

The existing popular light sources – incandescent lamps and fluorescent lamps have reached the limits in terms of optical conversion efficiency, colors, lifetime and application.

For instance, an incandescent lamp has good colors that can satisfy our eyes but its efficiency is only about 15lm/w and has a short lifetime (about 4000 hours). A fluorescent lamp has faced with so many improvements in lifetime (about 8000 hours) but it pollutes the environment and has poor colors. A sodium lamp is great in terms of efficiency and lifetime but it is poor in terms of colors and long heating time. Such problems stem from the spectrum of the discharged gas and the limited lifetime of the electrode to generate the light. To overcome the limitations in efficiency, lifetime and colors, new lighting technologies must be created.

Necessity for new lighting technologies

Since a long time ago, humans have been accustomed to the sun in nature. So, it is desirable to use a light source that closely resembles the sunlight.

Beside high energy efficiency and ability to discern the colors clearly, a long lifetime is required.

Recently, resource saving and environmental friendliness are emerging as new issues. From now on, we must also consider the social trend and the changes in human emotions including improved work efficiencies.

In addition, as resource saving and environmental friendliness are becoming increasingly important lately, some new lighting technology, power supplies and lighting devices are required to guarantee safety and freshness.

Energy crisis and CO₂ regulation

Since the mid 2000, the energy crisis with high gasoline prices and the global warming has led to stricter regulations of CO₂. The following international activities have taken place in relation to it.

Kyoto agreement: CO₂ emission prohibited (need to save the power)

RoHS: Hg free lighting (prohibited use of fluorescent lamps with mercury)

WEEE: wastes recovery (lighting, communication and convergence to minimize the wastes)

What is an LED?

An LED is more efficient that a incandescent lamp that converts electricity to light, and it can be used the same way as a fluorescent lamp. At the same time, as the RGB LED is developed, it can now crate a variety of colors.

Unlike a fluorescent lamp that contains mercury, an LED is mercury free and it is environment friendly since the wastes can be disposed freely. A lifetime of more than 50 thousand hours and 90% of improvement in electrical efficiency compared to an incandescent lamp with bad efficiency.

What is an LED lighting system?

Similarly to fluorescent or other discharge lamps, an LED lighting system is also composed of a stabilizer (or called driver) and a lighting device (adjusts the light optically and protects the system from the external impacts). Unlike the conventional light lamps in which one to four light sources are attached, an LED system can include numerous light sources.

Why does an LED need to control the current?

A lighting LED has a close relationship with the current and voltage. If the voltage is changed slightly, the current will be changed extremely. The luminous flux of an LED is in proportion to the amount of current and it can create big changes in the amount of luminous flux. If the current exceeds a certain limit, the lifetime of an LED is reduced and its luminous flux is also decreased severely.

Why is a heat sink important for an LED?

In general, an LED is classified as a cool light source from the perspectives of temperature. The optical output of a lighting LED is different from an incandescent lamp that discharges excessive infrared rays, and it actually has not infrared rays. (For some purpose of use, an LED sometimes generates infrared rays,) Although an LED lamp does not generate excessive infrared rays but it has high heats near the joint which must be discharged through a heat sink. Using a heat sink, the heat is discharged or an LED is operated at low temperature, so that we can achieve a large amount of luminous flux and a longer lifetime. Thus, a heat sink is very critical for an LED.

Role of an LED driver

An LED driver is equivalent to a stabilizer in a discharge lamp. It controls the current flowing to the LED. Up to now, no LED product or specs are standardized, so it is very important to search for a desirable driver.

Can an LED adjust the amount of luminous flux?

The DC current controls the optical output of an LED. By adjusting the DC current, you can control the amount of luminous flux. In addition, although the power of an LED is a turned on/off very quickly, the lifetime is not affected. So, you can use the method, so-called pulse width modulation. The pulse width modulation method controls the pulse intervals or durations to adjust the luminous flux of an LED. This requires very a high frequency to make it look like it remains on all the times. This problem can be easily resolved by using the direct digital control method.

Why is an LED affected by the heat?

In general, the lower the ambient temperature is, the higher the amount of LED’s luminous flux is. If the current and temperature are higher, then the junction temperature must rise as well. Therefore, some manufacturers are launching the products with built-in current control supplement devices that can maintain the amount of luminous flux at various temperature settings. However, these products operate an LED at high temperature that can reduce its lifetime. For instance, if an LED is operating within the current limit proposed by the maker at the general room temperature (20 to 25 degrees), then the junction temperature is ranged 60 to 80 degrees.