TY  - RPRT
TI  - Letter Circular 631: sun lamps, health lamps; carbon and mercury arc lamps (supersedes Letter Circular 462)
PY  - 1941
PB  - National Institute of Standards and Technology
CY  - Gaithersburg, MD
SN  - LCIRC 631
DO  - 10.6028/NBS.LCIRC.631
ER  -