Does anyone have any tips for light-proofing a tent (without blocking airflow)?

I’ve been exploring covering the air vents with the wooly matting that garden centers use to line the shelves that they keep potted plants on. It takes four layers to make it effectively opaque (when pressed against a bright lamp). It seems to still let plenty of air through, but I’m waiting for a tent and fan to arrive, so I can test things properly.

I’m getting a HomeBox Ambient, which have round vents that make it easy to tuck a few layers of matting in there, so I can easily try different things.

If there was a simple cover that kept direct sunlight off of the vent, you wouldn’t need four layers of the matting.

You can get similar matting material with activated carbon (which is used for carbon filters in cooker hoods). It wouldn’t replace a conventional carbon filter, but could be useful in some cases. It’s inexpensive, but I have no way to measure how effective the filtering is, so can’t meaningfully try it.

You can also get round plastic cans (as cooker hood carbon filters), which might permit unused duct-vents to be repurposed as opaque air vents.

Even if the carbon filtering is ineffective, it’d just be nice to let the air flow without the light getting in.