Let’s talk about Joules baby….

11. March 2010 by Brent.

Doing product comparisons? I’m just amazed when I read that a device puts out 60 joules per cm/2. What does that mean? Is it possible?

Let’s break it down. Imagine a rap video with this lingo in it. Snap! I need to add a Z to the end of my name.

This gets complicated, but I’ll try to simplify. By the way, not many light therapy device companies have this discussion because the average consumer doesn’t want it. They just want to know it works.

First: 1 square centimeter (cm/2) is how light is measured. 1 cm/2 can fit multiple LED’s (up to 4x Standard 5millimeter LEDS, also called T-1 3/4).

Second: Each LED has power used, vs light output (Radiant power or radiant flux). So for example, using 190milliwatts of power might be normal for 1 LED to consume, but it’s only going to convert 40milliwatts to actual light. We all know a regular light bulb uses a lot more power than it creates light which is why they are so inefficient and everyone wants to use LEDs now to light their homes. Even so LED’s are still only ¼ amount light vs energy used and that’s just the best white ones.

Third: Only Infrared LED’s are measured in Mill watts of light output. Colored lights are measured in MCD (milli candelas) and must be converted using a chart which represents our eye’s capability of seeing light. We see different colors easier than others so like a blue lights MCD can be lower but still put out higher Mill watts of light output.

There are lots of other complicated terms such as Angle of light from LED, Measuring in steradians, the distance from the light, Milliamps driving the LED, blah blah.

I’m trying to make this easy, but I think I’ve already lost myself, let alone anyone else. Come on Brent, get this summarized quickly.

So to summarize, One really really good 5mm Infrared LED can put out 15mw of light, if you put 4 together as close as possible you could get 45-60mw (although they would heat up so much they would go bad).

The formula for a Watt is: 1 Watt = 1 Joule per Second
Or
1 Joule = 1 Watt * 1 Second

Taking our 45-60mw * 60 seconds to see how many Joules per minute = 3.6 joules cm/2 per minute at very very best. There is a whole slew of reasons why this is even impossible for a home model, as running LED’s at that high output typically means they will overheat and when an LED overheats, it’s lifespan is decreased, and it’s radiant light actually goes down. It must be cooled via liquid, or enter into the laser arena to get more power than that.

So how can you get 60 joules per cm/2? You can use this device for 20 minutes. You could also mislead the people and say because it is a 4cm x 4cm area it puts out 60 joules, but this is misleading as no one measures it this way. You could say it’s 60 joules by measuring the amount of energy it uses, not the energy it puts out (like using a 60 watt bulb), again very misleading.

There are so many ways to mislead the consumer, so buyer beware. The best way to really know is to try it for yourself.

Did you make it to the end? I feel asleep 3 times writing this.

As always if you find my formulas or discussion problematic, feel free to email me or comment.

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