REED 8778 Heat Stress WBGT Meter


This heat stress datalogger measures temperature, humidity, and direct or radiant sunlight with Wet Bulb Globe Temperature (WBGT). With this information, the 8778 determines the "what it feels like" temperature. The 8778 is OSHA recommended and also features a user-adjustable WBGT audible alarm and the ability to adjust settings for indoor temperature measurement.


  • Heat Stress Index measures how hot it feels when humidity is combined with temperature, air movement and radiant heat
  • Black Globe Temperature (TG) monitors the effects of direct solar radiation on an exposed surface
  • In/Out function displays the WBGT value with or without direct sun exposure
  • User selectable unit of measure (°F or °C)
  • Large, easy-to-read LCD display
  • User adjustable threshold alarm (audible)
  • Tripod mount for long-term monitoring
  • Low battery indicator and auto shut off


Measuring RangesAir: 32 to 122.0°F (0 to 50.0°C)
Black Globe: 32 to 176°F (0 to 80°C)
WBGT: 32 to 122°F (0 to 50°C)
AccuracyAir Temperature: ±1.1°F (±0.6°C)
Black Globe (Indoor): 
59 to 104°F (15 to 40°C): ±1.8°F (1°C)
Rest of Range: ±2.7°F  (1.5°C)
Black Globe (Outdoor): 
59 to 104°F (15 to 40°C): ±3.6°F (2°C)
Rest of Range: ±2.7°F  (1.5°C)
Measuring Range0 to 100% RH
Accuracy10% to 90% RH: ±3%
Rest of Range: ±5%
Resolution0.1% RH
General Specifications
Response Time1 sec
Auto Shut-offYes (after 10 mins/off)
User Adjustable WBGT AlarmYes (audible)
Tripod MountableYes
Low Battery IndicatorYes
Power Supply2 AAA Batteries
Battery LifeApprox. 1000 hours (Alkaline)
Product CertificationsCE
Operating Temperature0 to 122°F (0 to 50°C)
Storage Temperature14 to 140°F (-10 to 60°C)
Operating Humidity Range0 to 95%
DimensionsInstrument: 10 x 1.9 x 1.1" (254 x 49 x 30 mm)
Black Brass Ball Diameter: 2.9" (75 mm)
Weight4.8oz (136g)