I'm new in the forum so sorry if my question was already previously asked. I tried to use the search function but I was not happy with the answer I got. So I have fun doing the light designer sometimes. I often see LED lights that are for instance 18x15 (270W). However when tested, the actual current consumption turns out to be less than that (about 200W usually). I've never been able to figure out why. Thanks guys and have a good day. Leo

  • \$\begingroup\$ Welcome to EE.SE. We'll need a link to a sample datasheet and a report on the measurements. Put all the information into your question and not in the comments. \$\endgroup\$
    – Transistor
    Jun 4, 2018 at 8:27
  • \$\begingroup\$ Wondering where you see those lights. Most simple lights are 36W. The old non LED PARs used to be in range 250-1000W. \$\endgroup\$ Jun 4, 2018 at 8:31
  • 1
    \$\begingroup\$ The universes of marketing and reality rarely overlap \$\endgroup\$
    – PlasmaHH
    Jun 4, 2018 at 8:43
  • \$\begingroup\$ They cheat, that's how. Sometimes the LED chip rating is a bit more than the power supply and cooling capability so they advertise the theoretical LED chip power. \$\endgroup\$
    – winny
    Jun 4, 2018 at 8:57
  • \$\begingroup\$ I consistently see that LED strips are underspecced by about one half. I just take that into consideration \$\endgroup\$
    – Makoto
    Jun 5, 2018 at 12:30

2 Answers 2


Because the world is full of charlatan vendors that like to confuse the buyer into thinking they are getting more than they are paying for.

The problem is 270 watts requires thermal management that includes expensive heatsinks and fans.

So they deceptively specify the wattage of the LED components but only drive it hard enough to where they begin to get hot.

The most important specifications I must know before buying an LED or LED light fixture, is the lumen output (or flux) and the total power used. I can then calculate the efficacy in lumens per watt. If it is an RGB, I want to know this spec for each color at 100% and the other colors turned off.

I do not care about the max rating of the LEDs. I will not buy from anyone that uses that technique as I do not like charlatan vendors. Also I would never buy an LED product that does not specify the flux output (lumens, radiant watts, or photons per second)

Charlatan vendors will often specify the wall watts and no flux. With no flux output specified you cannot compare the amount of light per watt. They could be using very inefficient (read cheap) LEDs and LED drivers.

For stage lighting I would use LEDs that are made with color mixing capabilities. Lumiled's Color C line and Color CZ are very good candidates. I also like deep red (660 nm) over "red" (625 nm). 625nm is really a red-orange where 660nm is a nice deep red. The only problem is that deep red has fewer lumens per watt so you would need more LEDs than red to get the same lumen output. Only Cree, OSRAM, and Lumiled make deep red. I prefer the OSRAM Oslon SSL 150.

There is an easy and inexpensive way to make your own stage lights that would be better and or less expensive. All you need is to generate the Gerber files for the circuit board. For example these guys have very inexpensive PCB fab and assembly: pcbway. And their quality is very good. Currently (June 2018) for $5 you can get ten 100mm x 100mm (4" x 4") boards and have them populated with up to 89 LEDs (e.g RG&B) for $88. Plus the cost of the LEDs.


LED modules often require an external driver circuit to limit the current. This can be as simple as a resistor or as complicated as a current limited buck/boost convertor.

LEDs will give off light even when not driven to their power rating. Underdriving them will actually increase their overall lifetime.

However marketing departments will often round up (significantly so) the power of LED modules because actual higher power modules are more expensive.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.