Bad news travels much quicker than good news. And in the social media age, it travels lighting fast. A bad product review can do much damage to a company’s reputation, so it makes LED lighting manufacturers a little uneasy when light meters are employed to determine the suitability of their lamps. 

source: licensedelectrician.com

For the most part, incident-light meters—hand-held devices used to measure the amount of light emitted from a source—are extremely useful, as they help to determine whether an illuminance level is optimal. Although LED lamp manufacturers specify lumen output of all lamps as well as beam angle lux output from the source to about 5m, light meters are still a viable tool to assist with:

• Product validation: Some manufacturers take “liberties” with their specifications, which explains why so many buyers are dissatisfied with their LED lamps once installed. A light meter is a relatively inexpensive way a buyer can validate a product.  The portability of a light meter allows on-site reading as well, providing hard, quantifiable data alongside “observational” data.
• Optimization: Depending on the buyer’s motivations or needs, a light meter can assist with optimizing energy use (ie. whether to increase or decrease the output level of luminaries at certain times of day) and determining safe and healthy levels of lighting.

But here’s why lighting manufacturers worry when a light meter reading is the sole determinate of a product’s suitability:  a light meter reading is only as good as the product, the user and reading technique, and the attention to maintenance.  Many retrofit jobs may be unsatisfactory as a result of inaccurate data from a light meter. The problem may not be in the lamp itself, but in the decision-making process of selecting that specific lamp for that specific task.

• Subpar products: While the level of performance of light meters has improved over the years, there are still many inferior products on the market. Some light meters claim accuracy for a specific light source (tungsten) at a specific color temperature (2856K). What happens to the accuracy outside of that? Other light meters claim accuracy of +/- 2% at a specific lux (500lux). Again, what happens to the accuracy at a different lux? It is not uncommon to hear of light meters with inaccuracies of 10%-15%. Furthermore, there are many light meters that are not properly certified, calibrated, and recognized by sanctioned standards, such as the American National Institute of Standards and Technology (NIST).
• Inexperienced operators: Like any technical product, it takes a reasonable amount of understanding to operate a light meter correctly. Combine a user with limited understanding with an inadequate light meter and the probability of purchasing the right lamp for the task seems low.
• Unsatisfactory maintenance: Calibration is generally valid for one year after a new purchase and many users fail to calibrate annually. To receive NIST-certified calibration, many light meter manufacturers ask users to mail the unit back for a fee so they can get it properly calibrated. The cost and inconvenience of going through this process annually is unappealing and as a result many light meters are not providing accurate readings.

Selecting the right lamp for the task is important and a light meter can help with the process. However, if the lighting evaluation process continues to be flawed, it’s likely that many LED retrofits will be inaccurately selected.

TIPS:

Ensure your light meter is recognized as a high quality product and that it includes a calibration certificate from NIST. Don’t forget to calibrate annually! If you are uncomfortable using the meter or are unsure of your readings, ask for assistance from a qualified lighting technician.