Inert gas In food packaging, inert gases are used as a passive preservative, in contrast to active preservatives like sodium benzoate (an antimicrobial) or BHT (an antioxidant). Historical documents may also be stored under an inert gas to avoid degradation. For example, the original documents of the U.S. Constitution is stored under humidified argon. Helium was previously used, but it was less suitable because it diffuses out of the case more quickly than argon. Inert gases are often used in the chemical industry. In a chemical manufacturing plant, reactions can be conducted under inert gas to minimize fire hazards or unwanted reactions.
Incandescent light bulb is 683 lm/W for monochromatic green light at 555 nanometers wavelength, the peak sensitivity of the human eye. The luminous "efficiency" is defined as the ratio of the luminous efficacy to the theoretical maximum luminous efficacy of 683 lpw, and, as for luminous efficacy, is of two types, radiant luminous efficiency (LFR) and source luminous efficacy (LFS). The chart below lists values of overall luminous efficacy and efficiency for several types of general service, 120-volt, 1000-hour lifespan incandescent bulb, and several idealized light sources. The values for the incandescent bulbs are source efficiencies and efficacies. The values for the ideal