For nearly 30 years, led strip lighting technology experienced a rapid development process. LED to its inherent high efficiency, long life and low loss, vibration resistance and response speed advantages such as a wide range of applications, such as a lamp, screen, traffic light and so on, are currently exploring it is applied to the lighting area.
Because China has not establish LED photometric standards, severely affecting LED quality improvement and the values of quantities of unity, affecting international trade and international technical communication between LED and promotion, therefore, although in recent years the Chinese quality and variety LED products have improved, but the gap with foreign advanced countries is obvious.
In this situation, we set out for the measurement of optical parameters LED the meticulous research, and LED the establishment of national photometric standards.
2, the LED Tube parameters are introduced
LED optical parameters of the important aspects in is: Flux, the luminous efficiency, luminous intensity, light intensity distribution, wavelength.
2.1 are The luminous efficiency and flux
The luminous efficiency is the ratio of the flux and power. The luminous efficiency represents the light source of energy savings of characteristics. It is to measure performance modern light source is one of the vital index.
2.2 are The luminous intensity and light intensity distribution
flexible led strip lighting luminous intensity is characterized in a direction of its luminous intensity, due to the different space angle in led light is quite different from that of strong, and we studied the light intensity distribution characteristics of bed. The parameters of practical significance are very big, directly affect the LED display device of the smallest view. Such as the sports facility LED large color displays, if choose LED single pipe distribution range is extremely narrow, so in the face of the larger screen angle viewers will see the image distortion. And the traffic signal lights also demand is bigger range of one can identify.
For LED spectral characteristics we basically see its monochromatic is fine, but also to pay attention to the red, yellow, blue, green, white LED and so on main color is pure. Because in many cases, such as the traffic lights to the color is asked to compare strictly, but according to observe some Chinese LED light now in some green, red for scarlet, from this phenomenon come to see us LED the spectral characteristics of special study is very necessary and very interesting.
3, LED photometric measuring principle
3.1 are The light intensity measurements
The light intensity standard light, LED and equipped with V (λ) filter silicon photoelectric diode installation and debugging in optical benches, especially strictly the filament position, LED parts and accept surface location.
For LED speaking, its shiny surface is the shape of the dome, light distribution is very special, so in different distance is measured, light intensity value will change from inverse distance square laws, even if fixed distance is measured, but because the receptors to accept different area, the light intensity value will also change. Therefore, in order to improve the measurement precision, should the distance is measured and accept area size to give relatively fixed as well. For example, distance is measured according to GIE recommends the 316mm, receptors area for 10 x 10mm fixed. In the same distance is measured. LED the corner is different, its brilliant light will be changed, so in order to get the best value, had better read the maximum readout Rt is preferred.
3.2 flux measurement method
Measuring leds luminous flux in angle changed the photometric on the turntable, installing the LED on the table, the table in the horizontal plane around the vertical axis rotation + 90 degrees, LED in the perpendicular plane around the metering axis rotate 360 degrees. the horizontal plane and the vertical plane of control is through the rotation of the stepping motor to fulfill. Turntable in guide rail move, when measuring standard lamp, turntable should leave guide.
When be measuring the big wheel in a perpendicular shaft revolves around a horizontal plane, step angle of 0.9, 90 the positive direction, 90 in the opposite direction. LED oneself moreover is in rotation, in every level angle, the vertical plane every 18 a signal acquisition, turn over 360 samples were collected after 20 data, press type calculating total flux.
Absolute flux measurement LED the second kind of method is integral method. This method is simple and feasible, but the measurement precision is not high.
The spectrum of light emitting diode power distribution measurement, the purpose is to keep the spectral characteristics and LED chromaticity, moreover is measured in order to have LED luminosity an amended.
When measuring spectrum power distribution LED, attention shall be paid to the following, in a standard irradiance spectra and comparison of solar spectrum because standard light intensity much better than LED, in order to avoid this problem, the best in the standard before the lights and a neutral filter, make its solar spectral intensity close to LED.
The spectrum width LED was exceedingly narrow, in order to accurately describe the spectral distribution LED outline, had better use the width of monochromator narrowband wavelength measurement for 1nm wavelength interval for good.
4, last word
At present, the LED country photometric standards established and calibration equipment has been quite a number of standard LED tube, in the process, we have accumulated a lot of experience, and then we will at all levels and the comprehensive measuring department LED production units for dissemination, unified supervision. This LED to the quality of China will increase the level of play a role in promoting, also for countries in the field of high technology research and development from a to provide security.