John,
This guy works in a welding supply house??? The higher the number the lower the luminous transmittance (lets less IR thru) A bigger danger with the small geometery welding filter would be to locate the sun by eye and then try to place the filter between you eye and the sun.
Place the filter over your eyes and then try to find the sun. The attached table will give you an idea (sorry about the indentation)
Al
TABLE EP-1--FILTER LENS SHADE NUMBERS FOR PROTECTION AGAINST RADIANT ENERGY
Shade
Welding operation number
Shielded metal-arc welding 1 1/16-, 3/32-, 1/8, 5/32-inch
diameter electrodes........................................................ 10
Gas-shielded arc welding (nonferrous) 1/16-, 3/32-, 1/8-,
5/32-inch diameter electrodes.............................................. 11
Gas-shielded arc welding (ferrous) 1/16-, 3/32-, 1/8-,
5/32-inch diameter electrodes.............................................. 12
Shielded metal-arc welding 3/16-, 7/32-, 1/4-inch diameter electrodes...... 12
5/16-, 3/8-inch diameter electrodes........................................ 14
Atomic hydrogen welding.................................................... 10-14
Carbon-arc welding......................................................... 14
Soldering.................................................................. 2
Torch brazing.............................................................. 3 or 4
Light cutting, up to 1 inch................................................ 3 or 4
Medium cutting, 1 inch to 6 inches......................................... 4 or 5
Heavy cutting, over 6 inches............................................... 5 or 6
Gas welding (light), up to 1/8-inch........................................ 4 or 5
Gas welding (medium), 1/8-inch to 1/2-inch................................. 5 or 6
Gas welding (heavy), over 1/2-inch......................................... 6 or