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Posted By: davidcycleback

If you have a UVA/UVB (longwave/shortwave) blacklight, you can test how any material protects against UV light. Sunlight has UVA & UVB light, which is what damages cards and photos and gives you a sun tna/burn. For example, if a card fluoresces brightly under UVA light (normal blacklight), but doesn't when mylar is put in between, that means the material blocks UVA light. If the card continues to fluoresce, the material doesn't block UVA.

Normal window glass blocks UVA but not UVB, with UVB being the more damaging. The collector wants holders, glass and suntan lotion that blocks both UVA and UVB-- but normal glass offers better than no protection.