Three PID lamp energies are sold across portable and fixed VOC detectors, 9.8/10.0 eV, 10.6 eV, and 11.7 eV, and the choice is set entirely by the ionisation energy (IE) of the target compound versus the photon energy of the lamp [S3][S7]. A 10.6 eV Krypton-filled lamp is the industry default because it covers benzene, toluene, xylene, and most other common VOCs while delivering a service life near 10,000 hours, roughly a year of continuous duty [S4].
An 11.7 eV lamp extends the detectable set upward into chlorinated and higher-IE species, but in published field accounts that extension costs roughly an order of magnitude in service life, with some users reporting lamp replacement cycles measured in weeks [S4]. That is why Honeywell's BW Ultra portable is offered only with the 10.6 eV SR-Q1-4R replacement sensor, with no 11.7 eV variant available [S1].
How lamp photon energy gates which VOCs a PID can see
A photoionisation detector only responds to molecules whose ionisation energy is at or below the lamp's photon energy, so the lamp effectively defines the detector's analyte list [S3][S7]. A 10.6 eV lamp ionises hydrogen sulfide (IE ≈10.5 eV) plus everything below it, including aromatics, olefins, most ketones, and many amines, but it cannot see methanol (IE 10.84 eV), formaldehyde (IE 10.87 eV), or chloroform (IE 11.37 eV) [S3].
Compounds with IE above 11.7 eV, including methane (IE 12.61 eV), carbon dioxide (IE 13.78 eV), and the permanent gases, are not PID-detectable at all on standard lamps, which is why PIDs are specified as VOC/inorganic-selective rather than total-hydrocarbon instruments [S3][S7]. In practice, the decision is rarely "PID or not", it is which of the three lamp tiers matches the target compound's IE.
10.6 eV lamp: coverage, life, and why it is the default
The 10.6 eV Krypton lamp is described across vendor and integrator sources as the standard, rugged, and most common PID lamp, suitable for benzene, toluene, xylene, and the broad envelope of hydrocarbons found in fuel vapors, solvents, paint booths, and soil-screening work [S2][S5]. Typical service life is around 10,000 hours, just over one year of continuous operation, which sets the maintenance budget for a fixed PID loop [S4].
For benzene-specific monitoring, integrators often drop to a 9.6/9.8 eV lamp and pair it with a selective filter cartridge so that interfering aromatics are excluded, leaving benzene as the dominant response [S4]. This is a deliberate trade: lower photon energy = smaller detectable compound set, but a longer-lived lamp and a much cleaner reading on a single analyte. The 10.6 eV sits in the middle, broad enough for general VOC surveys, durable enough for fixed installation, and inexpensive enough that rental fleets and OEM portables standardise on it [S1][S5].
11.7 eV lamp: where it earns its keep and what it costs
The 11.7 eV lamp exists to push the PID response window upward to compounds such as chloroform (IE 11.37 eV), dichloromethane (IE 11.32 eV), and other chlorinated solvents whose IE sits above the 10.6 eV ceiling [S3]. ION Science guidance and integrator write-ups both note that for these high-IE analytes the 11.7 eV lamp is necessary, and that no lower-energy lamp can substitute [S3][S6].
The cost is lamp life. Published figures describe 11.7 eV lamp life as "a few months" in general service and "a very short life (weeks)" in harsher duty, driven mainly by sputtering of the metal ring inside the lamp envelope that coats the window and reduces UV output [S3][S4]. That is acceptable in a portable instrument used intermittently, and unacceptable in a fixed detector that must run unattended, which is why fixed-system integrators avoid 11.7 eV unless the chemistry demands it [S4]. Sensor and instrument vendors therefore sell 11.7 eV as an option or specialty SKU, not as a standard fit, and some popular portable SKUs such as the BW Ultra do not offer it at all [S1][S6].
Decision matrix: 9.8 eV vs 10.6 eV vs 11.7 eV
Three criteria drive the choice: target-compound IE, expected service interval, and instrument form factor. The table below summarises how the three common lamp options compare on those criteria, drawn from vendor and integrator sources [S3][S4][S5][S6].
9.8/10.0 eV: lowest photon energy, longest practical life, narrowest coverage; best for benzene-specific work with a filter cartridge, used where excluding interferences matters more than breadth [S4]. 10.6 eV: standard Krypton fill, ~10,000 h life, covers benzene plus most common VOCs; the right default for general industrial-hygiene, confined-space, and leak-detection work [S3][S4]. 11.7 eV: extends coverage into chlorinated solvents and other high-IE species, but life drops to weeks-to-months and many portable SKUs do not offer it; specify only when the target IE forces the choice [S1][S3][S4].
Application routing: which lamp fits which job
For industrial-hygiene surveys covering fuels, solvents, and paint-booth emissions, a 10.6 eV lamp is the correct fit and the one rental fleets standardise on for general-purpose PIDs [S2][S5]. For benzene-specific fenceline or hot-work monitoring, a 9.6/9.8 eV lamp plus a selective filter cartridge is the established pattern, since the lower photon energy suppresses most non-benzene interferences [S4].
For chlorinated-solvent or methylene-chloride process monitoring, only an 11.7 eV lamp responds, and the specifier must budget short lamp-replacement cycles or accept a portable-only deployment [S3][S4][S6]. For methane, CO, CO2, or other permanent gases, no PID lamp works, and a different sensing technology is required, which is why fixed gas cabinets often pair a PID gas detector for solvent leaks with a separate pressure transmitter loop and a catalytic or IR sensor for the LEL fraction.
Standards, safety envelope, and sourcing notes
PID instruments used for personal safety fall under the IEC 60079 family for explosion protection in hazardous areas, and the lamp/electronics assembly is treated as a single safety-certified subassembly on certified portables such as the BW Ultra [S1]. Industrial-hygiene deployments additionally reference the relevant occupational exposure limits (TWA/STEL) that the PID read-out is benchmarked against, and the lamp choice does not change those limits, only which compounds the instrument can see at all [S3].
For buyers comparing 10.6 eV and 11.7 eV total cost of ownership, the dominant variable is lamp replacement frequency, not instrument price: a 10.6 eV lamp running ~10,000 h is replaced roughly once per year in a fixed loop, while an 11.7 eV lamp can demand replacement on a weekly-to-monthly interval in continuous service, a difference that quickly dwarfs the sensor-module cost [S4]. Where the process gas set includes both common VOCs and a high-IE chlorinated component, integrators typically deploy two parallel PID loops on different lamps rather than try to force a single sensor to cover the full IE range, an approach that also keeps each industrial valve and sample-conditioning train sized for one analyte class.
For broader gas-detection architecture, including how open-path and point detectors complement each other on a fenceline, see this open-path gas detector limitation note. For instrument-level safety interlocks that may be driven by a PID alarm, the PID controller reference covers the loop-tuning side of that interface.