Buying a 5-watt LED bulb is nothing mysterious. In fact, we can already get them in packs of five or ten units at very reasonable prices. However, when we talk about a 5-watt laser, the story changes completely, and handling it requires several safety measures. So, if the definition of the watt is not altered, what is the difference between 5 watts that barely illuminate a room, and 5 watts that can blind a person...?
Let's start with the basics: the watt is a measure of power. Its job is to quantify the rate of energy transfer, and it equals one joule per second. The problem is that we see the expression watt everywhere, applied to almost anything. Overuse combined with lack of details leads to very strange and confusing situations, for example, comparing 5-watt LED bulbs with 5-watt laser modules used in engraving metal, wood, and other materials. That brings us to the Brainiac75 channel, who decided to explore the difference between these '5 watts':
LED bulb versus laser
In relaxed terms, everything comes down to the type of energy: when you take the box of a bulb and see its power is 5 watts, it's actually a 5-watt electrical input, with a light output equivalent to that of an old 40-watt incandescent bulb, much less efficient. In contrast, the laser is a 5-watt optical energy output, a measure of the light power coming from the diode. The electrical input of the laser Brainiac75 uses is about 20 watts, and the bulb's optical output is approximately 1.2 watts.
Now, 1.2 watts in a laser could do a lot of damage. Why doesn't anything happen with the bulb? The key is intensity, also known as power density or power per unit area, measured in watts per square meter. When calculating the light emission surface of the 5-watt LED bulb (5.7 in its final measurement), its intensity is about 128 W/m² at the aperture, and 15 W/m² at five centimeters away. Applying that same calculation to the laser, the result jumps to 700,000 watts per square meter at the aperture, while at its focal point five centimeters away, we're talking about 475 million W/m².
And what about lumens?
For a good part of the video, Brainiac75 demonstrates what a 5-watt laser can do, but at the end he explores the great advantage of the LED lamp, which is in its lumens. The lumen is a unit of luminous flux, and it takes into account aspects such as the human eye's perception.
Brainiac75's LED bulb reaches about 470 lumens, but when calculating the laser's luminous flux using its 450 nm wavelength as a reference, the laser's effective 5.7 watts generate only 253 lumens. The perceived power in the laser light is lower, but in practice it is much stronger... and dangerous.
Source: Brainiac75 on YouTube
