what is UV BLOCK quartz?

[secretmicrogrow420]

hello i just noticed my CMH bulbs have "UV BLOCK QUARTZ" and im wondering what does this mean? please someone chime in

 

[Jjgrow420]

They're dual jacketed with quartz to limit the amount of UV that passes through

 

[secretmicrogrow420]

They're dual jacketed with quartz to limit the amount of UV that passes through

thank you so much for the info i appreciate it!