Color temperature consistency is a core indicator of the light quality of a straight tube lamp, especially in demanding lighting environments such as commercial and exhibition lighting. Color temperature deviations can lead to visual discomfort and compromised brand display effectiveness. Achieving color temperature consistency requires collaborative optimization across multiple stages, including raw material selection, phosphor coating processes, chip sorting, heat dissipation design, production process control, and finished product testing, forming a comprehensive quality control system.
The purity and proportion of raw materials are fundamental guarantees. The phosphors in straight tube lamps must be mixed in strict proportions. For example, the ratio of red, green, and blue phosphors in a tri-color phosphor must be precisely controlled. Deviations in the proportion of any component can cause a shift in the color coordinates when synthesizing white light. Simultaneously, the light transmittance of the glass tube must be ≥90%. Low-lead glass (lead content ≤0.1%) reduces the interference of impurities on the light color, preventing localized color temperature deviations due to uneven light transmission. Furthermore, the purity of the inert gas (such as argon or krypton) must be ≥99.99%, with an oxygen content ≤0.001%, to prevent gaseous impurities from participating in the discharge reaction and altering the light color.
The phosphor coating process directly affects the uniformity of light color. When coating the inner wall of a straight tube lamp with phosphor, it is necessary to ensure a uniform coating thickness (typically 10μm-20μm) through spraying or dip coating. If the coating is too thick or too thin in some areas, the emitted light will appear yellowish or bluish. The spraying pressure needs to be controlled between 0.2MPa and 0.3MPa, and the glass tube lifting speed during dip coating needs to be stable (5cm/s-10cm/s) to avoid coating bubbles or sagging due to uneven flow rate. After coating, it needs to be dried in an oven at 80℃-100℃ for 30min-60min to cure the adhesive and form a firm and uniform phosphor coating, preventing light color attenuation due to coating peeling.
Chip sorting is a key step in controlling color temperature consistency. The dominant wavelength range of LED chips needs to be controlled within 2.5nm, but due to process limitations, it is difficult for a single batch of chips to fully meet this requirement. Packaging manufacturers typically divide chips into multiple binning units (e.g., 16 small binning units) based on parameters such as wavelength and color temperature. The color temperature deviation of each binning unit is controlled within a small range (e.g., ±150K). During straight tube lamp production, chips from the same binning unit must be specified to avoid inconsistent color temperatures across the entire lamp due to differences in chip color temperature. If chips from multiple binning units are used, color temperature balancing requires complementary color mixing techniques (e.g., using a combination of three chips from different binning units), but this method increases costs.
Heat dissipation design is crucial for color temperature stability. During straight tube lamp operation, an increase in chip junction temperature leads to luminous flux attenuation and color temperature drift (especially in high color temperature lamps). Optimizing the lamp tube structure (e.g., adding heat sinks, using thermally conductive silicone) improves heat dissipation efficiency, ensuring the chip junction temperature remains stable within a reasonable range (typically ≤85℃). Poor heat dissipation alters the ratio of blue light emitted by the chip to yellow light converted by the phosphor due to temperature changes, resulting in color temperature shift. For example, when heat dissipation is insufficient, high color temperature straight tube lamps may experience a decrease in color temperature (becoming yellowish) due to faster blue light decay.
Production process control relies on statistical tools and real-time monitoring. An SPC (Statistical Process Control) system is used to dynamically monitor key parameters such as protective film powder weight, phosphor powder weight, and inflation pressure. An X-S control chart automatically determines whether a process is abnormal. For example, if the phosphor powder weight fluctuates beyond the set range, the system will trigger an alarm, allowing technicians to adjust the spraying equipment parameters in a timely manner to avoid color temperature deviations caused by uneven powder weight. Simultaneously, Pareto charts can analyze the source of defects (such as an excessively high coating defect rate at a certain workstation) and guide targeted improvements.
Finished product inspection is the last line of defense for color temperature consistency. A spectrometer integrating sphere system is used to measure the total luminous flux, chromaticity value, and color tolerance (SDCM) of the straight tube lamp. If the color tolerance is >5 (some scenarios require <3), it is considered unqualified. In addition, aging tests simulating real-world usage scenarios are required (e.g., 100-200 hours of operation at rated voltage), with luminous flux measured every 20 hours. Lamps with an attenuation rate >5% must be discarded. For straight tube lamps with adjustable dimming and color temperature, color temperature stability under different brightness levels must also be tested to ensure color tolerance meets standards (e.g., McAdam 3rd order) during dimming.
Color temperature consistency control for straight tube lamps must be implemented throughout the entire supply chain, from raw materials and processes to testing. By rigorously sorting chips, optimizing phosphor coating, enhancing heat dissipation design, implementing statistical process control, and conducting full inspection of finished products, color temperature stability can be significantly improved, meeting the high requirements for light quality in commercial lighting, high-end displays, and other scenarios.
