1. What is the transmission rate?
Light transmittance is an important parameter for evaluating the material’s ability to transmit light. Simply put, it describes how much energy is retained after the light passes through the material. When the light shines on the surface of the material, it will experience three different fates: part of it is reflected back to form our common reflection; part is absorbed inside the material and converted into heat energy; only the remaining part can successfully penetrate the material and become transmissive light.
The calculation method of light transmittance is intuitive and clear: the ratio of transmitted light throughput to incident light light is multiplied by 100% and converted into a percentage. A glass with 90% light transmittance means that it allows 90% of the incident light to pass through, and only 10% of the light is reflected or absorbed.
2. The actual use scenario of the transmission rateIn the automobile manufacturing industry, the light transmittance of the windshield is directly related to driving safety. Too high will cause too much glare, and too low will affect the driving vision at night. China’s standards clearly stipulate that the light transmittance of the front windshield of the car should not be less than 70%.In the display industry, the light transmittance of mobile phones and TV screens affects the display brightness and color reproduction. Higher light transmittance means that brighter images can be obtained at the same backlight intensity, or lower power consumption at the same brightness.In the packaging industry, the light transmittance of beverage bottles and plastic wrap is not only related to the product display effect, but also closely related to the shelf life of the contents. Many food and drug packaging need low light transmittance to prevent deterioration caused by light.
In the construction industry, the light transmittance of glass curtain walls affects the indoor lighting efficiency and the energy consumption of air conditioning. It is necessary to find a balance between high light transmittance (increasing natural light) and low light transmittance (reducing heat accumulation).
In the optical industry, transmittance has different effects on imaging systems/energy transmission systems/and spectral analysis.
3. The core principle of light transmittance determination
To understand the principle of light transmittance measurement, we need to start from the interaction between light and materials. When a beam of light hits the surface of the material, it is immediately divided into three channels: the reflected light bounces back from the surface to form a mirror image; the absorbing light is “swallowed” by the material and converted into other forms of energy; the transmissive light successfully passes through the material and continues its journey.
For the real light transmittance measurement, it is the last part that needs to be accurately captured – the transmitted light.
4. Commonly used transmittance measurement methods and equipment
1. Stometer measurement method
The spectrophotometer is the most accurate and comprehensive tool in the measurement of light transmittance, which can count the passage of light wavelength by wavelength.
Its working principle is to separate the mixed light into a single wavelength light through a monochrome, so that it is received by the detector after passing through the sample, and compare it with the original light intentity to calculate the light transmittance. Continuously scanning different wavelengths can draw a complete light transmittance spectral curve.
2. Sample processing of spectrophotometer(1) For solid materials such as glass and plastic sheets, it must be ensured that the surface is clean and scratch-free, and the sample needs to be placed vertically.(2) For liquid samples such as solutions and oil products, it is necessary to use a special quartz colorimeter to avoid bubbles, so as not to cause reading distortion.(3) Calibration before measurement: First, use air or pure solvent as a “blank” sample, and set the instrument to 100% light transmittance; then use a shading plate to simulate the completely light-transmitting state and set it to 0%. After these two calibration points, the instrument has established an accurate measurement benchmark.
There are many different types of spectrophotometers: visible spectrophotometers focus on the visible light area of 400-760 nm; ultraviolet-visible spectrophotometers extend the measurement range to 200-1000 nm and can evaluate the light transmission performance of materials in the ultraviolet region, such as sunscreen glass and optical filters.3. Fog meter
The haze meter is specially used to measure the “fog” caused by the internal scattering of the material – that is, the degree of blurring of the image after the light passes through the material. Through a precise integrated spherical optical system, it can accurately separate the total transmitted light into parallel transmitted light and scattered transmitted light. The ratio of total transmitted light to incident light is the transmittance, and the ratio of scattered light to total transmitted light is the fog. It is used for screen film, packaging film and other scenes that need to control transparency and imaging quality.
Five. Key factors to ensure the accuracy of measurement
No matter which instrument is used, several key factors need to be paid attention to to obtain accurate light transmittance data:1. Prepare the samples. The solid surface must be clean and pollution-free to avoid the influence of fingerprints and dust; liquid samples should be uniform and free of suspended matter; film samples should be flat and free of folds.2. Carry out instrument calibration regularly. Regularly use standard samples to verify the instrument status to ensure the comparability and accuracy of the measurement results.3. Control the environmental conditions well. Ambient light and temperature fluctuations may interfere with the measurement results, especially when using portable equipment for on-site testing, the influence of strong direct light should be avoided as much as possible.4. Choose the instrument according to the needs. Laboratory research and development requires accurate spectral data, and spectrophotometer is the ideal choice; the production line is fast quality inspection, and the light transmittance meter is more efficient; optical material evaluation, the fog meter provides more comprehensive information.