GB/T 23595.2-2025 is Part 2 of the series of test standards for rare earth phosphors for LEDs. It specifies the method for determining the relative brightness of such phosphors under excitation by ultraviolet to blue light in the wavelength range of 350 nm to 480 nm. This standard applies to the performance evaluation of phosphors used in fields such as lighting and displays. The core of the standard involves exciting the phosphor with quasi-monochromatic light, converting the optical signal via a photoelectric detector corrected with a visual function, and calculating the relative brightness based on the brightness of a standard phosphor. The test requires the use of a spectroradiometer (with an excitation spectrum half-peak bandwidth ≤1 nm), a photoelectric detector meeting the requirements of a Class I illuminance detector, along with specific standard phosphors and sample trays. The test is conducted in a dark environment at 25°C ± 5°C and a relative humidity of <65%, providing a unified basis for product quality control.