You mean "Blacklight"- That is Ultraviolet? Well, you may go for it. Some glass bottoles show fluorescence in UV, and choose the wavelength that can particularly shine inpurities of glass. You might be well able to see strain field of glasses as well if you use polarizer for UV ray and then pass through polarization analyzer. Use lower wavelength UV for better penetration, and use FIR filter as well. If you tend to use Hard-UV or soft X-ray, chances are that diffraction from crystalline impurities would be readily detected. You need some radiation-deterring protection as well. White Light or IR would be difficult to manually observe or put strain on eye of observer (but it may reduce cost, especially if you put workers at risk and put them physically in side of production line), but since UV is invisible, data capturing , image analysis and interpretation are already bulit into the system. So- you get it!

Hello dear Sumit Bhowmick, good time,

Thank you for your time and information.

Piotr Garbacz previously reviewed the use of UV backlight in the "INSPECTION OF TABLEWARE GLASS PRODUCTS AT THE HOT END OF PRODUCTION LINE" paper and concluded that "Industrial trials have shown that this method cannot be used due to the significant reduction of the fluorescence effect with increasing temperature".

I want to use visible or infrared backlight but I don't know, which one is better!?

BR.