White shirts early light

What you’re describing is a bit unusual because most clothing is designed either to block light (UV protection, sun shirts) or to provide modesty and cooling. If your goal is to get as much early-morning and late-evening light exposure as possible while still wearing a shirt, look for fabrics with:

• Open knit construction rather than tight weave

• Light colors (white, cream, pale gray)

• Low fabric weight (under ~120 gsm if listed)

• Linen or linen blends

• Burnout tees (partially sheer)

• Loose-knit cotton tees

• Athletic mesh training shirts with larger perforations

Some options that allow significantly more light through than a standard cotton T-shirt:

Fabrics ranked by light transmission

1. Mesh athletic shirt – most light reaches the skin, but appearance can be sporty.

2. Burnout tee – semi-transparent and often surprisingly comfortable.

3. Loose-knit linen tee – cool, breathable, and lets some light through.

4. Thin white linen shirt (unbuttoned) over a tank or bare chest – common in hot climates.

5. Standard lightweight cotton tee – blocks much more light than most people realize.

One thing to keep in mind: even a thin white shirt reduces the amount of light reaching your skin substantially. However, if your interest is in circadian rhythm and morning sunlight, your eyes are generally much more important than skin exposure. Being outside facing the dawn sky for 10–30 minutes without sunglasses often provides a much larger circadian signal than trying to maximize light through clothing.

For your 6 a.m. river walks, a loose white linen T-shirt or a lightweight mesh training shirt would probably be the closest match to what you’re describing: cool, comfortable, and allowing considerably more light through than a normal tee while still being fully dressed.