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Lightning Detection & Lightning Detectors


by the National Lightning Safety Institute

Lightning hazards can be mitigated by advanced planning. One part of this safety program should include an early detection and warning alarm package. Lightning detectors can give notice to shut down dangerous operations before the arrival of lightning. They also may signal “all clear” conditions after the lightning threat has passed. Some type of detection package may help you with Duty-To-Warn issues.

Lightning detectors vary in complexity and cost from large dedicated equipment packages costing in excess of $150,000 to inexpensive $20-$30 Radio Shack portable weather radios. The Flash-to-Bang (F-B) Method requires no dedicated detector — only counting the time in seconds from seeing lightning’s flash to hearing the associated thunder or bang. For each five-second interval, lightning is one additional mile away. Thus, a F-B of 10 = 2 miles, 15 = 3 miles, 20 = 4 miles, etc.

The distances from lightning Strike A to Strike B to Strike C easily can exceed more than five miles. How much time is needed to get to shelter? Three to four minutes is suggested. Suspension of activities is very site-specific. For general situations, we recommend activating your lightning defense at a F-B of 30: lightning is six miles away. We also recommend waiting to resume activities for 30 minutes after the last observed lightning or thunder. This protocol may seem excessively conservative in many situations. (“We’ll never get anything done under such strict guidelines....”). Lightning safety is a case-by-case risk management decision. And, yes, safety and productivity sometimes are incompatible. Safety, however, always should be the prevailing directive.

Available technologies of present day lightning detectors include:
  1. Radio Frequency (RF) Detectors. These measure energy discharges from lightning. They can determine the approximate distance and direction of the threat. See Boltek Lightning Detection Systems.
  2. Inferometers. These are multi-station devices, much more costly than RF detectors. They measure lightning strike data more precisely. Inferometers usually require a skilled operator. See Vaisala Lightning Detection.
  3. Network Systems. The National Lightning Detection Network and the United States Precision Lightning Network systems cover all of the USA; each reports lightning strikes to a central station. Local storm data is available by subscription. Past strike information is archived and accessible upon request. See NLDN and USPLN.
  4. Electric Field Mills. This pre-lightning detection equipment measures potential gradient (voltage) changes within the earth’s electric field and reports these changes as thresholds build to lightning breakdown values. For more on EFMs, see Mission Instruments and Campbell Scientific, Inc.
  5. Optical Monitors. These can provide earlier warning, as they detect cloud-to-cloud lightning that typically precedes cloud-to-ground lightning.
  6. Hybrid Designs. These monitors use a combination of the other single-technology designs. Two or more sources of information (C-C, C-G, optical recognition, EFM) may be better than just one. See Wxline.
  7. Subscription Services. NLSI Recommendation: Rent a meteorologist. Here hired professionals make the critical decisions and advise you. This method may blunt claims of negligence if something goes wrong. And some subscription weather services provide windspeed, rain, hail, tornado and other data sets. Off-site lightning detection by subscription is available from several vendors, including Skyview Weather, AccuWeather, Inc., DTN/ (Weather Sentry) and WeatherData Services, Inc. (Sky Guard).

Lightning Detection Options —
Accuracy vs. Cost vs. Complexity

Source of Info Accuracy Cost Complexity
Is Near
No Cost Simple
TV Weather
No Cost Simple
Up to $40 Simple
Up to $500 Moderate
Up to $1500 Moderate
Up to $7000 Moderate
Monthly Fee Simple

Beware of a false sense of confidence imparted by detectors; none of them will detect all lightning all of the time. None of them will provide “first strike / Bolt Out of the Blue” information or forecast in advance the precise locations of lightning strikes. Various detection receiver algorithms operate at different frequencies and wavelengths: Boltek Stormtracker in the Low Frequency Range 100-700 kHz; Vaisala GAI NLDN at 100-400 kHz; NMT Lightning Array at VHF 60-78 mHz; NASA LIS and OTD optical at 777.4 m; Vaisala SAFIR VHF at 109-119 mHz; Vaisala GAI LDAR II at 50-120 mHz; GAI VLF at 20-50 kHz; the UK Meteorological Office RDI at 9.8 kHz; etc. An excellent summary of families of lightning detectors and future research is available at NASA’s Lightning Detection Instruments.

Detectors can display early warning of lightning conditions to hazardous operations. Some detectors can start/stop standby power generators. A signaling or alarm notification method is essential to alert field personnel of developing dangerous circumstances. Two-way radios, remote-activation siren packages, strobe lights and other methods are available.

Essential companions to any type lightning detector include:
  1. A written Lightning Safety Policy;
  2. Designation of Primary Safety Person;
  3. Determination of When to Suspend Activities;
  4. Determination of Safe/Not Safe Shelters;
  5. Notification to Persons at Risk;
  6. Education:  At a minimum consider posting information about lightning and your organization’s safety program;
  7. Determination of When to Resume Activities. For many situations, if you hear thunder, your (brain) detector is working fine. Since lightning and thunder always occur paired, the lightning associated with the thunder you just heard is within your hearing distance — some seven to nine miles. Immediately go to safe shelter. No place outside is safe!
Select the detector and/or signaling device that is site-specific to your requirements, is easiest to use, and which offers the most favorable cost/benefit to your operation’s budget. No detector is 100% perfect.

Summary:  Detectors give advanced notice of the lightning hazard. Now consider other defenses to mitigate the hazard. Where is safe refuge? How long to get there? How long to stay there? What about computers and servers and telecommunications? Is facility bonding and grounding and surge protection OK? Lightning rods required? Contact NLSI for assistance.

Authored by the National Lightning Safety Institute (NLSI).  Previously published in print; Exclusive online publication 25 April 2008 by Ten Spider Enterprises; modified for the web. Article Copyright National Lightning Safety Institute; Used with Permission.

Follow links to the right to learn more about lightning detection and lightning detectors. At the left margin, Related Links address topics of interest pertaining to lightning and thunderstorms, including lightning protection, lightning safety, and other lightning and severe weather topics. View the Weather & Meteorology SiteMap for a complete list of meteorology and weather-related topics.

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