We are often asked what the wattage of our Chip on Board LEDs are and this is not always easy to determine. This post will cover an explanation of how one can determine how many watts these lights draw as well as compare them to their outdated counter-parts: Incandescent Light Bulbs.
See also for more context on calculating wattage
Incandescent vs. LED: Comparing Ratings
Our COB lights list parameters such as Flux that have some measurements of mW and some measurements of lumens, Current - Test, Forward Voltage, Lumens/Watt, and Current Max so it can be a little confusing to determine which wattage is being asked for. In the older fluorescent fixtures and incandescent models, all bulbs were rated with voltage, current, and wattage. These fixtures didn’t have many active components to start with (if any) and the technology didn’t need complex terminology. When LEDs were developed, an equivalent rating had to be developed because the devices draw way less than the older technology. When I used to work in a department store, there were ratings typically saying that around an 8.5W LED is nearly equivalent to a 60W incandescent bulb in most cases after comparing brightness/luminosity. So in that case, a 60W COB is like a 424W incandescent bulb! Many stores will have this type of equivalency rating, but does not always hold constant. It is always recommended to read all the data available for the chips because wattage does not equal brightness.
COB Wattage Calculation
This is why luminous flux and lumens per watt were added to the terminology because the new product is so much brighter and more efficient. To find the wattage that the bulb physically draws, there has to be an assumption that the right voltage (around the forward voltage) is being used. I typically just use the forward voltage to determine the wattage. It is up to the individual to use either the test current, maximum current, or both for being thorough. Use the top formula below for what I would call the Test Power or the bottom formula below for what I would call the Maximum Power.
In reality, the power drawn by the component will not be constant because there are more factors like heat dissipation, operating temperature, operating conditions, and even design of the surrounding circuitry can change the power values. These calculations are for a reference as the design will heavily impact the actual amount of power consumed, the measured values will be around PTest or PMax.
Comparison to Incandescent
To do a rough comparison to an incandescent bulb for reference, here is the equation:
The PLed can be calculated from PTest or PMax and the only unknown variable is PInc which is what would be solved for using algebra or a graphing calculator. This will not be an exact estimate as more factors go into equivalencies, but should give a rough idea compared to incandescent. Also, not all LED chips will be brighter as they can be designed to put out less lumens than the incandescent counter-part. In this case, look at the lumen values.