Irradiance and Red Light/Near Infrared Bulbs
Irradiance is the technical term for intensity of light. Irradiance can apply to both visible light, which can be seen with the naked eye, and infrared energy, which is not perceptible to the naked eye. Whether the light/energy is visible or not, its irradiance decreases as distance from the source increases. (Think of how a lightbulb seems much brighter when you are beside it than when you are across the room from it.) For this reason, irradiance data always includes the distance from the source, such as .33M, .5M, 1M. Irradiance is measured in milliwatts per centimeter squared(mW/cm2), with larger irradiance numbers indicating more energy available at that distance.