The Truth About LED Lumens
Why is it you can replace some lights with more ‘advertised’ lumens with a LED light with less lumens. Here are 4 reasons:
1. Focused Lumens
LED light is directional, conventional light sources are omni-directional and require reflectors to gather the light and focus it to where it is needed. Any reflection that is over 1 bounce effectively loses the effect of the lumen. It has been proven that you can lose up to 30% of the effective lumens in the reflective process.
2. Quality of Lumens
This is related to CRI, and the best explanation is seeing how much better you can see when comparing LED to High Pressure Sodium. It is not uncommon to have customers tell you that 20,000 lumens of LED appear brighter than 60,000 lumens of HPS. The basic truth is you need less quantity when you have higher quality.
3. Photopic vs Scotopic Lumens
This has to do with how a camera perceives lumens and how humans perceive lumens. Photopic lumens are lumens that are detected by a device that is similar to a camera. Light meters register photopic lumens. Scotopic lumens are lumens detected by the human eye. LED produces light within these spectrum’s, which means the light perceived by LED is light that we use. It is rare to see a LED light produce IR or UV spectrums. These wavelengths are invisible to people, so they have no value to us from a vision perspective.
The science of scotopic lumens is associated with a factor that allows us to adjust the photopic value to give a true representation of how useful the lumens are. The factor, developed by scientists, is an attempt to level the playing field. The factor is used to adjust the effective value of the lumen, either up or down from the advertised photopic lumen listed on the package. Some lights, like HPS, have a factor that reduces the lumen amount. LED, on the other hand, typically has a factor of 1.7 or greater, which means the lumens it is producing is far more effective to us. Therefore, less lumens is required to do the job. Recently, light meters have been developed that display both photopic and scotopic levels.
4. Lumen Degradation
It is not uncommon for HID bulbs to have lost a significant amount of its initial lumens after only 5000 hours of life. Yet these bulbs are rated for 15,000-20,000 hours. This means the customer is using a bulb that is performing poorly for the next 15,000 hours of life. As well, as lumens degrade, so does CRI. This translates to a significant drop in effective lumens or light quality.