Extech HD400 Light Meter

The HD400 is a rugged light meter that measures a wide range to 4,000 Fc or 40,000 Lux using a precision silicon photo diode and spectral response filter with cosine and color corrected measurements. Peak mode (10 mS) captures highest reading, and Relative mode indicates change in light levels.

Backlit LCD display with 40-segment bar graph; peak mode (10 mS) captures the highest reading; relative mode indicates change in light levels; minimum/maximum; data hold; low battery indicator; and a built-in USB port for real-time monitoring and storage of light level data on a PC.

A light meter measures the amount of visible light, also known as illumination, in a given area. For many meter brands, including Extech, illumination is expressed in units of measure called Lux (for metric) and foot-candles (used in the US). To use an Extech light meter, the sensor is placed on a tabletop or other surface in the area to be measured and the light level reading is indicated on the meter's display.

There are many different types of lighting that can be measured. the most common are: sodium, tungsten, mercury, and fluorescent. The following list shows common applications for each lighting type.

• Sodium lighting: Highway, parking lots, security measurements
• Tungsten lighting: Sunlight and incandescent lighting measurements
• Mercury lighting: Highways, parking lots, stadiums
• Fluorescent lighting: Indoor lighting for workstations and store display areas