Shade numbers, switching time and arc eye

A common misunderstanding: the filter is not what stops arc eye. The polycarbonate and the permanent UV/IR coating in an auto-darkening cartridge block ultraviolet continuously, at every shade, powered or flat. That protection does not switch.

So what does switching time do

It controls exposure to intense visible light. A filter switching in 0.04 milliseconds admits a far shorter flash than one at 0.5 milliseconds. Over hundreds of strikes in a shift that difference is felt as eye fatigue and headache rather than injury.

Choosing a shade

• MMA to 150A — shade 10 to 11.
• MIG at 150 to 250A — shade 11 to 12.
• TIG at low amperage — shade 9 to 10, and check the filter is rated to trigger at low current, since a small TIG arc can fail to wake a cheap cartridge.
• Plasma cutting — shade 5 to 8 depending on current.

The real risks

Two things genuinely cause arc eye. A cracked or pitted outer lens, which loses the coating that does the work — replace it, they are pennies. And bystanders: the ultraviolet from an arc reflects off light walls and reaches people who never look at it directly. That is what screens are for.

Written for Arcline Welding Supplies — a demonstration store. See the AgenticEcom Suite.