Extech lt4045 lux meter for standard lighting white leds and coloured leds extech lt40 the extech led lt40 light meter is used for monitoring and optimizing environmental light levels in buildings schools and offices led lighting is being used more commonly because they are less expensive more energy efficient and brighter model lt40 measures the light intensity for white led lights or standard lights the lt40 has a built in sensor with protective cover and is supplied with 2 x aaa ba