Westinghouse offered a special mercury lamp in the 400 watt version with a yellow heat-resistant stain applied to the bulb's exterior for a saturated yellow light to identify "caution" locations. These lightbulbs were used at railroad crossings, dangerous cloverleaf merges on highways/freeways and other locales whereby other than the usual bluish-white mercury lightbulbs were typically used. These 400W bulbs were electrically interchangeable with the other 400 watt ones offered.

The example shown is new-old-stock and still was in its protective plastic baggie during the photograph (the outside of these bulbs scratched very easily like automotive amber bulbs).