testo 540

The Hazard Usually Assessed by Opinion

Most workplace hazards get measured. Gas gets a detector, noise gets a meter, dust gets a monitor. Lighting tends to get a look around and an opinion.

That’s a gap, because poor lighting contributes to slips, trips and falls, to errors and quality problems, and to eye strain and fatigue across a shift. It’s also one of the easier things to fix once you know where the problem is.

Australian interior and workplace lighting requirements are set out in the AS 1680 series, with recommended illuminance levels that vary by the task being done rather than by the room. A drawing office and a corridor have different requirements, and the only way to know whether either is being met is to measure at the working plane.

A lux meter turns “it seems a bit dark in here” into a figure that can be compared against a requirement, recorded in an assessment and used to justify a change.

Why the Sensor Has to Match the Eye

This is the technical point that separates a lux meter from a light sensor, and it’s why a phone app isn’t a substitute.

Lux isn’t a measure of radiant power. It’s a unit weighted to how sensitive human vision is at each wavelength. The eye is most responsive to green light around 555 nanometres and falls away sharply towards red and blue, so two light sources giving off identical power can look very different in brightness.

A raw light sensor doesn’t account for that. It responds to wavelengths the eye barely registers, so its reading describes the radiation present, not how bright the space looks to a person standing in it.

The testo 540 uses a silicon photodiode with its response adapted to the spectral sensitivity of the eye. That’s what makes the number a lux value. Accuracy is ±3 lux or ±3% of reading, whichever is greater, against a Class B reference to DIN 5032 Part 7.

The Range, and What It Covers

Zero to 99,999 lux sounds like an odd span until you consider what it has to cover.

A poorly lit store room might sit under 50 lux. An office is typically several hundred. A workshop doing detailed assembly needs considerably more. Direct daylight through a window can reach tens of thousands. One instrument has to handle all of it, which is why the resolution steps down as the range goes up: 1 lux up to 19,999 lux, and 10 lux above that.

The measuring rate is half a second, which matters on a survey. Checking whether a floor meets its requirement means measuring at a grid of points rather than one, and an instrument that takes several seconds to settle turns a twenty minute job into an hour.

Built to Be Carried

At 95 grams including the protective cap and batteries, the testo 540 fits in a shirt pocket. A clip on protective cap, belt holder and wrist strap keep it safe. Two AAA batteries run for about 200 hours without the display light.

The hold function freezes the current reading, which is what you need when the sensor is held at the working plane and the display is facing away from you. Maximum and minimum values are shown at the press of a button, which is useful where lighting is cycling or a survey covers a range of conditions.

The display is illuminated, and units switch between lux and foot candles. It’s supplied with a calibration protocol, and an ISO calibration certificate is available as an option.

Where It Fits

A lux meter is one of the more frequently used instruments in an occupational hygiene kit, because lighting comes up in almost any workplace assessment.

It sits naturally alongside other environmental measurements. On a workshop visit, lighting can be checked on the same trip as other hazards. On an HVAC or building services survey, illuminance is often on the checklist alongside temperature, airflow and carbon dioxide.

Where It’s Used

Offices and commercial buildings. Workshops and fabrication areas. Warehouses and distribution centres. Retail and shopfront lighting. Schools and lecture theatres. Hospitals and aged care. Laboratories. Plant rooms and switchrooms. Carparks and stairwells. Emergency exit routes. Mine site offices and workshops. Occupational hygiene and WHS assessments generally.