# LED light power specifications



## garyS-NJ (Mar 18, 2015)

I've bought a few LED spots and floods and small led car dome lights and even a monster 300W lightbar and none of them draw the current I'd expect at 12VDC. (the car dome lights) and otherwise most of the lights say something like 9-32VDC input (so they work on 12V or 24V DC systems). When I buy an 18W light from say Kawell, I'd expect it to draw 1.5 amps but it measured 1 amp. I think every light I ever measured drew about 1/2 to 2/3 of the current I expected.. (and note that I am running with supplies that can source the current at 12VDC,,,

I attributed this to Chinese sellers over stating their specs but I think there could be more to the LED light power specifications,. this link has some weird stuff talking about 1W LEDs and 3W LEDs current draw... what am I missing? (note that I am presently looking at buying some lights for my friend's boat and considering bars that use multiple 3W, 5W, or 10W LEDs (you can find my other thread if interested!).

https://www.hydrogrowled.com//LED-Technology-LED-Basics-What-is-a-LED-W67.aspx#bas5

"LED wattage classifications have been made very confusing by manufacturers such as Cree, Osram and Luxeon, for example a 1W LED is driven at 350mA of current; however a 3W is driven at 700mA. Even though the 3W has only double the current of a 1W, it is somehow classified as consuming triple the wattage."


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## Timothybil (Mar 18, 2015)

One of the greatest advantages of LEDs beyond the greater efficiency/less wasted energy factor is the fact that the color temp of the light emitted varies very little in relation to the amount of light emitted, as opposed to an incandescent light that changes color temp drastically as the current changes.

My understanding is that the wattage rating of an LED is the maximum at which that LED can be safely driven, not the wattage currently being supplied. Let's take the example of a Cree XM-L LED. When driven at close to its maximum rating, it is capable of putting out around 1,000 lumens of light, yet by controlling the amount of current being sent to the light, the output can be as little as 1 lumen. This is part of the function that the driver circuit provides, and is what allows a light to have multiple output modes. In light of this, let me rephrase your last sentence. _Even though the 3W has only double the current *being consumed* as the 1W, it is still classified as *being capable of consuming* triple the wattage_.

As far as your first paragraph, I think the important part is the 9-32VDC input statement. Wattage consumed can be stated as the number of amps of current being drawn *at the specified voltage*. Did you measure the amperage consumed when connected to a bench power supply or while in circuit on a vehicle? Remember that when a lamp on a vehicle is specified as being 12v, it may actually be fed with anything from 10-11v when the vehicle is off, to 14-15v when running. Given that the driver circuit is providing in this example 1.5A at 12v, the amperage being drawn from the source could vary from 1.2 to 1.8A.


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## idleprocess (Mar 19, 2015)

garyS-NJ said:


> I attributed this to Chinese sellers over stating their specs but I think there could be more to the LED light power specifications,. this link has some weird stuff talking about 1W LEDs and 3W LEDs current draw... what am I missing? (note that I am presently looking at buying some lights for my friend's boat and considering bars that use multiple 3W, 5W, or 10W LEDs (you can find my other thread if interested!).


I blame Lumileds and the Luxeon. Roughly ten years ago, they were the only name brand when it came to power LED's. There was the Luxeon I _(which ran at ~1W)_, the Luxeon V _(which ran at up to ~5W in a 4-die series-parallel arrangement)_, then the Luxeon III _(which was basically a Luxeon I rated for up to ~triple the current and ~3W)_. This lead to power LED's being referred to by part wattage rather than whatever actual power levels they were driven at - either by the LED manufacturer (Lumileds' exclusive on power LED's was short) or by companies that made luminaires/flashlights/etc - resulting in a slew of "1W", "3W", "5W", etc claims. In a market where incandescent efficiency had been pretty static for decades, claiming higher wattages for LED products suggested higher brightness.



garyS-NJ said:


> "LED wattage classifications have been made very confusing by manufacturers such as Cree, Osram and Luxeon, for example a 1W LED is driven at 350mA of current; however a 3W is driven at 700mA. Even though the 3W has only double the current of a 1W, it is somehow classified as consuming triple the wattage."


This is probably a result of how the forward voltage of the LED *inherently* changes with the drive current. Look at page 5 of the Cree XM-L2 data sheet and examine the "Electrical Characteristics (TJ = 85 °C)" chart. Note that at a drive current of 200mA, forward voltage is ~2.67V _(~534mW)_ while at 3000mA it has risen to ~3.35V (4.69W) - a 15-fold increase in current has resulted in an 18.82-fold increase in wattage. Older-technology LED's (used by many off-brands) have an even more pronounced voltage shift with rising current.


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## SemiMan (Mar 19, 2015)

garyS-NJ said:


> I attributed this to Chinese sellers over stating their specs




Trust your first instinct. No one (reputable) rates the "wattage" of a light by the LEDs, they rate it by lumens/lux/power draw. If you buy an 800 lumen bulb, you expect 800 lumens. If you buy a 10W bulb, you expect 10W draw, not 5 .... unless it is an 800 lumen bulb rated at 10W that is only drawing 5 watts and putting out 800 lumens.

No one outside EBAY/Alibaba sellers really talks about "wattage" of the LED much any more. 1W/3W is historical from the Luxeon1/Luxeon3/Luxeon5 world as IdleProcess pointed out. Be wary of anyone rating any lighting product in "watts" unless it is an incandescent bulb.


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## garyS-NJ (Mar 19, 2015)

yes Timothy, I'm using bench supplies with plenty of current but nothing over 12.5VDC. I suspect if I run these lights closer to their max input voltage, they may run closer to their advertised power. And yes, I am dealing with ebay and amazon and wonder if I'm really getting cree or osram./. These sellers add up the LEDs for power but most publish theoretical and actual lumens (I have no way to measure lumens but measuring current at voltage is easy enough..).

as for forward voltage and current, I looked at the cree datasheet and I think the low forward voltage at 700MA was just getting it to turn on and then otherwise it was pretty stable. then the light and heat was proportional to forward current.

I think my answer regarding power is that I will draw current proportional to my input voltage applied (boat or car at 12-14VDC) and that is how bright my light will be. nice that I'll be in the middle of the voltage range for reasonable junction temps and for good relilability/life.

my bigger question going into all this tho was trying to decide which light bar was better, many smaller LEDs or fewer larger leds. My budget and the market is limited tho and so I think im zeroing into a pair of lightbars around 100W with a combination of spot and flood. probably made with the OSRAM 5W fisheyes. I'll aim them one in front of the other and switch independently.


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## Timothybil (Mar 19, 2015)

garyS-NJ said:


> my bigger question going into all this tho was trying to decide which light bar was better, many smaller LEDs or fewer larger leds. My budget and the market is limited tho and so I think im zeroing into a pair of lightbars around 100W with a combination of spot and flood. probably made with the OSRAM 5W fisheyes. I'll aim them one in front of the other and switch independently.


I think the answer there is to look at the reflectors. As a rule of thumb, the deeper and/or narrower the reflector, the smaller the hot spot and the more throw and less spill. Look at the differences between the Nitecore TM11 and TM15, aside from the rechargeable feature, they are basically the same light. The only difference is that the TM15 has deeper reflectors. Thus it throws further and has less flood than the TM11.

I'm going to stick my neck out here and hazard a guess that the light bar with the smaller LEDs is going to have shallower reflectors, due to space constraints, and therefore not throw as far as the bars with the fewer larger LEDs. If you go to Illumn.com and look at their light bars, they have a link to some comparison photos showing their lights in use. It might help you decide. Good luck and enjoy your lights.

BTW, if no one has said it before, Welcome to CPF!:welcome:


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