When writing about LED lighting for portraits, readers always ask: Are they really daylight balanced? And how bright are they? Most LED lights are rated in lux (luminous flux), which doesn’t help most photographers, especially when there’s a distance component affecting the inverse square rule that “an object twice the distance from a light source will receive a quarter of the illumination.”
The above is not a bracketed series because all three unedited frames were made at the same exposure—1/60 sec at f/2/8 and ISO 800. That’s because some LEDs lights have a problem called Pulse Width Modulation, which can cause flickering while appearing to be continuous light when it’s not.
Experience in the movie industry with LEDs show most exposure meters are not properly balanced to read LEDs and that can sometimes, but not always, result in inconsistent exposure. One exception is the Sekonic C-700 SpectroMaster Spectrometer that’s capable of reading all light sources whether they’re LED, flash, incandescent, HMI, fluorescent or in the natural light spectrum. They are not inexpensive, however. The C700 runs about $1500.
In this kind of shooting situation, mirrorless cameras have an advantage because you can see exposure variations in the viewfinder, no chimping required and re-shoot if necessary I always use a Pocket Diffraction Grating Spectroscope to analyze the quality of lights. These can be found on eBay for about $30 and are typically used by rock and gem collectors to analyze the quality of light passing through a stone.
Light output from LEDs can be harsh and in the past some of my portrait subjects remarked to me about it and yet it didn’t bother others. When that happens, I either used a lighting modifier like a shoot through umbrella and that seems to do the trick.