Lumens, luxes and candelas - and how to measure them

Manufacturers of portable lighting specify luminous flux (lumens) and other details according to different standards and conditions. Therefore, it can sometimes be difficult to compare products from different brands. We measure the luminous flux ourselves and indicate the measured value in the description of each product (Measured luminous flux:).

Definitions

• Luminous Flux (lumen, lm): Often referred to in everyday language as brightness. It is the unit that measures the total amount of light emitted by the light source. The lumen value is not affected by the reflector’s surface or the shape of the light beam.
• Intensity (candela, cd): The greater the intensity, the longer the range. The narrower the beam pattern of a light source, the further the light reaches. If the beam pattern is adjustable (zoom function), intensity increases when the beam narrows, thus extending the range. Note that intensity does not indicate the total luminous flux (lumens).
• Illuminance (lux, lx): Lux is the unit of illuminance, indicating how much light reaches a surface. 1 lux = 1 lm/m². Lux values are generally not comparable unless the measurement distance is known. If the distance is known, candela (intensity) can be calculated.
• Range (meter, m): The maximum distance at which the light source can illuminate an area with at least 0.25 lux, which is approximately equivalent to full moonlight. The range can be directly calculated from the intensity. (Read more under “Light Laboratory / Range.”)

Different practices for specifying luminous flux

The industry follows various practices when specifying the characteristics of a light source. Understanding these different standards can be confusing, and it is often difficult to determine which figures can be trusted. If the lighting performance is presented according to the ANSI/NEMA FL1 standard, the values should be specified under the same conditions. This means that when measuring according to ANSI/NEMA FL1, at least the same parameters are being assessed.

Unfortunately, even large, well-respected manufacturers sometimes manipulate figures despite claiming adherence to the ANSI/NEMA FL1 standard. As an independent testing entity, we have invested in our own light measurement equipment to present the most accurate and honest performance data for the products we offer.

OTF (Out-the-Front) Luminous Flux

OTF refers to the actual luminous flux emitted from the light when the reflector and lens are installed. This means the amount of light coming from the complete product that the customer receives. It does not refer to the maximum theoretical luminous flux of the LED core, which is always higher than the OTF value.

We always measure OTF, as the ANSI/NEMA FL1 standard requires OTF measurements.

The LED Core’s Maximum Theoretical Luminous Flux

For many lighting products, manufacturers do not measure or disclose the OTF luminous flux. Instead, they list the maximum luminous flux that the LED core can produce under optimal laboratory conditions and print that value on the packaging.

For example, an XM-L2 LED core can theoretically deliver over 1300 lumens under perfect conditions. However, when used in flashlights, the measured OTF luminous flux ranges from 350 to 1100 lumens—yet manufacturers often print "1300 lumens" on the packaging.

Manufacturer Markings

The actual luminous flux can vary significantly, and the numbers on the packaging do not always reflect reality. Some manufacturers do report OTF luminous flux, but they measure it immediately after switching on the light—without pre-loading the flashlight. Since OTF values can drop significantly after just a few seconds, the flashlight should always be tested under pre-loaded conditions, as required by ANSI/NEMA FL1.

Some manufacturers and retailers simply display the highest value they can justify, even if it does not reflect real-world performance. For example, a flashlight with an XM-L2 LED core that actually produces around 600 lumens (OTF) might be labeled "1600 lumens", despite this being impossible to achieve even in optimal laboratory conditions.

Why Is It So Difficult to Specify the Correct Luminous Flux?

Measuring luminous flux requires advanced and expensive equipment. Factory-grade measurement tools can cost hundreds of thousands of dollars, making them inaccessible to most manufacturers and retailers.

Few people can verify luminous flux values.

Because so few have the capability to measure light output accurately, manufacturers can label products with almost any values they want. Since higher numbers tend to sell better, manufacturers have a strong incentive to inflate their figures.

Valostore’s Measurement Technique

We always measure lighting OTF, meaning we determine the actual luminous flux. We also measure intensity (candela) and calculate the range correctly. Although we follow the ANSI/NEMA FL1 standard, there is one minor exception:

The standard requires testing at least three units, but since this is a time-consuming process, we usually test one or two randomly selected units instead. On all other points, we strictly follow the ANSI/NEMA FL1 guidelines. We always pre-load the product being tested to eliminate any initial peak output, which could otherwise lead to an artificially inflated measurement result.

Even though our measurement method is not 100% ANSI/NEMA FL1-compliant, it provides a highly reliable reference. Our measurements are directly comparable to other reliable measurement data, as long as actual OTF lumens are being assessed. In product descriptions, we present our own measured values under the label: "Measured Luminous Flux".