COB Lights Versus Incandescent Lights

terminology

#1

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will cover an explanation of how one can determine how many watts these lights draw as well as compare them to their outdated counter-parts: Incandescent Light Bulbs.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.

P_{Test}=I_{Test}*V_{forward}
P_{Max}=I_{Max}*V_{forward}

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:

\frac{8.5W}{60W}=\frac{P_{Led}}{P_{Inc}}

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.


#2

One should also note that unlike incandescent bulbs, the wattage value one derives for an LED light source such as a COB does not necessarily correspond to a brightness value. A higher-wattage LED might not necessarily be brighter than a lower-wattage one, and double the wattage does not mean double the brightness or vice-versa. Wattage figures for LEDs should generally be used to calculate the power requirements for your device, not used as a means of brightness comparison as is the case for incandescents.

EDIT: To clarify as per Kaleb’s comment below, I’d meant to state that two 60W LED devices would not necessarily have similar brightness levels, rather than a 60W LED and a 60W incandescent. Wattage on an LED device has little to do with its luminous performance; one shouldn’t assume that one COB which draws 60W of power will perform the same as another COB which also coincidentally draws 60W of power, unlike the assumption that one 60W incandescent bulb is pretty much the same as any other.


#3

Matt is correct, not all 60W LEDs will be brighter than their incandescent counter-parts, but many times it is generally true. If my assumption is not turning out valid, then the luminosity values will matter.