My other answer just touches the tip of the iceberg.
It answered the main question How Is Intensity of Blue Light Measured?
Actually my previous answer was for a different question:
How Is Luminous Flux of Blue Light Measured?
LEDs are generally spec'ed in Luminous Flux. Luminous Intensity is a whole different thing.
But that's not all, Intensity is often confused with Illuminance and Luminance.
So we have four methods of measuring the amount of light emitting from an LED.
- Luminous Flux
- Luminous Intensity
No one has asked the question what is the difference between these 4 measurement.
But that's not all. I touched on this in the previous answer.
The above 4 measurements relate only to Photometric units of measure.
The three basic units of light measurement are:
- Photometric (photometry)
- Radiometric (radiometry)
- Photonic (quantum)
Radiometry is the study of optical radiation of light, ultraviolet radiation, and infrared radiation. Radiometric is a measurement of the actual flux emitted from the light source.
Photonics measures light as quantum particles called photons. Photons are elementary particles of light which carry light's electromagnetic force. Photons, travel in straight lines at the speed of light, and carry a fixed amount of energy. Photons have two distinguishing characteristics, direction and wavelength. Photons are a quantum measurement of light particle energy measured in the quantity of photons per second. Typically measured with some sort of photon detector which counts the number of photons that hit the detector's surface within a period of time.
Photometry, is about human optical visual response to light (luminous spectral response). Photometric is a measurement of the flux emitted from the light source and then adjusted for its sensitivity to the human eye. Photometric measurements only includes light visible to humans. The human eye is most sensitive to green at a wavelength of 555nm (Lime Green) as determined by the CIE (International Commission on Illumination). This 555nm wavelength is the international photometric standard to which all other wavelengths are compared.
This sums it up, almost
Then there are the official SI Units of Measure
If that is not confusing enough
I have not begun to touch on the various LED datasheet parameters that significantly affect the decision making process.
- Luminous, Radiant, and Photon Flux
- Luminous and Radiant Intensity
- Luminous and Radiant Efficacy
- Thermal Resistance
- Total Included Angle
- Viewing Angle
- Radiation Pattern or Spectral Distribution.
- Forward Voltage
- Forward Current Max
- Forward Voltage vs. Current
- Current vs. Relative Radiant / Luminous Flux
- Flux vs. Temperature
- Package Thermal Management Design
- Thermal Resistance LED Junction to Thermal Pad
- Forward Voltage vs. Temperature
- Color Rendering Index (CRI)
I am fairly confident that most engineers use Luminous Flux (lumens) as the major criteria in LED selection decision making.
Using just the Lumens Spec from the Datasheet is a huge, yet very common, mistake.
Of the 16 parameters in the above list there is one that I have found to be the best parameter to quickly assess an LED. It's not Lumens.
I would bet a fair amount of money that no one reading this would pick which ONE of the 16 parameters is the most decisive.
I could tell you, but that should be another Question.
Another coll question would be: Why and How are Most White and Green LEDs made from Blue LEDs.
Hint: Ever notice that White LEDs have a yellow coating?
That brings up another Question, Why are these LED Light Bulbs Made Like This?
This is actually going to be a very important thing when manufacturing a Blue Sleep Light. While some of the Sleep Studies found it required about 250-300 lumens. But would five 50 lumen blue LEDs do the job? Not likely.
Phillips goLiteBlu Energy Light
Isn't $150 a lot for a Blue LED light? There is a good reason it costs this much. If you knew, you would consider it a bargain.
I design Research Grade LED grow lights and so does Phillips. Phillips does a pretty good job, one of the best.
I'm not a normal engineer. I look at things from a different perspective than most and connects the unconnected dots. Advice from an old man, maybe even wisdom, Do not attempt to be normal, it will rob you of the opportunity to be extraordinary.
UF LED Research Paper Two of the authors, Thomas A. Colquhoun and Kevin M. Folta are the guys I do the LED grow lights for.