question: difference between watts and lumens

[yaml]

i see that some lights indicate their "watts" and others their "lumens"; how do you compare the two when trying to decide on brightness? which is a better indiction of relative brightness? thanks

 

[Bobby]

Watts is the amount of energy required to make power. In our case the power that is made is light. Unfortunately there are many many ways to make that light which can be drastically different on how efficiently the light is made. That means that two lights that have the exact watt draw could have one putting out x amount of light and the other putting out 2,3,or 4x the amount of light. Watts tells you nothing about the amount of light, only the amount of energy draw to create it.

Lumen tells the amount of light at its source. This is good for comparing if the manufacturers are using good numbers to determine that output. Unfortunately it can be difficult to compare because of how a lot of lights specifications are published. It is a decent starting point though.

Not sure what kind of light you are in the market for, and yes we are a light manufacturer, but we have a comparison of common primary lights over a fairly broad range that might be helpful.

 

[3D diver]

There are watts, lumens, candelas, Chinese lumens...none really measured consistently, some pure hype. Bobby is right, a lot depends on your application...peeking in holes, night diving, cave diving, focus light, video light, tech diving, recreational diving, etc.

LED's tend to be quoted in lumens, usually the LED manufacturers rating. The actual output can vary since they may be binned (i.e. sorted and sold by light output) and their output depends on how they are driven.

Post up what you are looking for and you'll get lots of advice...most good.

 

[Oldbear]

... yes we are a light manufacturer, but we have a comparison of common primary lights over a fairly broad range that might be helpful.

Nice videos on your website...

 

[KeithG]

Watts is what goes in, lumens is what comes out.

 

[lucca brassi]

watt goes out also as waste - temperature .

It is possible to talk about watt- lumen ratio as efficiency of light source in relation lm/W (normaly we take light source as pure sourceLED emiteriself , HID bulb , Incandescent...)

[TABLE="class: wikitable"]

[TR]
[TH="colspan: 7"]Cost Comparison[/TH]
[/TR]
[TR]
[TD][/TD]
[TD]Incandescent[/TD]
[TD]Halogen[/TD]
[TD]CFL[/TD]
[TD]LED (Generic)[/TD]
[TD]LED (Philips)[/TD]
[TD]LED (Philips L-Prize)[/TD]
[/TR]
[TR]
[TD]Purchase price[/TD]
[TD]$0.41^[23][/TD]
[TD]$4^[24][/TD]
[TD]$4^[25][/TD]
[TD]$10^[26][/TD]
[TD]$16^[27][/TD]
[TD]$30^[28][/TD]
[/TR]
[TR]
[TD]Electricity usage[/TD]
[TD]60 W[/TD]
[TD]42 W[/TD]
[TD]13 W[/TD]
[TD]13.5 W[/TD]
[TD]12.5 W[/TD]
[TD]10 W[/TD]
[/TR]
[TR]
[TD]Lumens[/TD]
[TD]860[/TD]
[TD]570[/TD]
[TD]825[/TD]
[TD]850[/TD]
[TD]805[/TD]
[TD]940[/TD]
[/TR]
[TR]
[TD]Lumens/Watt[/TD]
[TD]14.3[/TD]
[TD]13.6[/TD]
[TD]63.5[/TD]
[TD]63[/TD]
[TD]64.4[/TD]
[TD]94[/TD]
[/TR]
[TR]
[TD]Color Temperature Kelvin[/TD]
[TD]2700[/TD]
[TD]3000[/TD]
[TD]2700[/TD]
[TD]3000[/TD]
[TD]2700[/TD]
[TD]2700[/TD]
[/TR]
[TR]
[TD]CRI[/TD]
[TD]100[/TD]
[TD]100[/TD]
[TD]82[/TD]
[TD]>75^[29][/TD]
[TD]85[/TD]
[TD]92[/TD]
[/TR]
[TR]
[TD]Lifespan (hours)[/TD]
[TD]2,000[/TD]
[TD]3,500[/TD]
[TD]8,000[/TD]
[TD]25,000[/TD]
[TD]25,000[/TD]
[TD]30,000[/TD]
[/TR]
[TR]
[TD]Bulb lifetime in years @ 6 hours/day[/TD]
[TD]1[/TD]
[TD]1.6[/TD]
[TD]3.7[/TD]
[TD]>11.4[/TD]
[TD]>11.4[/TD]
[TD]>13.7[/TD]
[/TR]
[TR]
[TD]Energy cost over 10 years @ 15 cents/kWh[/TD]
[TD]$197[/TD]
[TD]$138[/TD]
[TD]$43[/TD]
[TD]$44[/TD]
[TD]$41[/TD]
[TD]$33[/TD]
[/TR]
[TR]
[TD]Total[/TD]
[TD]$201[/TD]
[TD]$166[/TD]
[TD]$55[/TD]
[TD]$54[/TD]
[TD]$57[/TD]
[TD]$63[/TD]
[/TR]
[TR]
[TH="colspan: 7"]Comparison based on 6 hours use per day (21,900 hours over 10 yrs)[/TH]
[/TR]

[/TABLE]

 

[tadawson]

Noting that those are source efficiencies, and not the overall light . . . did a bit of searching, and it appears that HID has a lumens/watt rating of around 120 . . . . a data point notably absent on this chart, which appears to be pushing LED technology . . .

- Tim

 

[3D diver]

Watts is the energy you'll waste, and What's are the questions you'll be asking, if you try to figure out light ratings.







Sorry, couldn't resist...

 

[lucca brassi]

there is some more comparations

Luminous efficacy - Wikipedia, the free encyclopedia

and if you login uder CREE you can searsh through their products Cree Product Characterization Tool

interesting is also economical aspect like :


[TABLE="width: 100%"]

[TR]

[TD="class: content, width: 147, bgcolor: #1e67ac"]Category[/TD]

[TD="width: 118, bgcolor: #1e67ac"]
Design Parameter
[/TD]

[TD="width: 66, bgcolor: #1e67ac"]

Unit​

[/TD]

[TD="width: 324, bgcolor: #1e67ac"]
Explanation (all parameters vary by
current)
[/TD]
[/TR]

[TR]

[TD="width: 147, bgcolor: #999999"]
LED Parameters
[/TD]

[TD="width: 118, bgcolor: #999999"]
LED VF
[/TD]

[TD="width: 66, bgcolor: #999999"]

V​

[/TD]

[TD="width: 324, bgcolor: #999999"]
Forward voltage of LED
[/TD]
[/TR]

[TR]

[TD="width: 118, bgcolor: #999999"]
LED W
[/TD]

[TD="width: 66, bgcolor: #999999"]

W​

[/TD]

[TD="width: 324, bgcolor: #999999"]
Power consumption of LED
[/TD]
[/TR]

[TR]

[TD="width: 118, bgcolor: #999999"]
LED LM
[/TD]

[TD="width: 66, bgcolor: #999999"]

lm​

[/TD]

[TD="width: 324, bgcolor: #999999"]
Luminous flux of LED
[/TD]
[/TR]

[TR]

[TD="width: 118, bgcolor: #999999"]
LED LM/W
[/TD]

[TD="width: 66, bgcolor: #999999"]

lm/W​

[/TD]

[TD="width: 324, bgcolor: #999999"]
Efficacy (lumens per Watt) of LED
[/TD]
[/TR]

[TR]

[TD="width: 147, bgcolor: #999999"]
Price Parameters (values will be blank if Price =
$0)
[/TD]

[TD="width: 118, bgcolor: #999999"]
LM/$
[/TD]

[TD="width: 66, bgcolor: #999999"]

lm/$​

[/TD]

[TD="width: 324, bgcolor: #999999"]
Lumens per dollar of LED
[/TD]
[/TR]

[TR]

[TD="width: 118, bgcolor: #999999"]
$/LM
[/TD]

[TD="width: 66, bgcolor: #999999"]

$/lm​

[/TD]

[TD="width: 324, bgcolor: #999999"]
Dollars per lumen of LED
[/TD]
[/TR]

[TR]

[TD="width: 118, bgcolor: #999999"]
c/LM
[/TD]

[TD="width: 66, bgcolor: #999999"]

¢/lm​

[/TD]

[TD="width: 324, bgcolor: #999999"]
Cents per lumen of LED
[/TD]
[/TR]

[TR]

[TD="width: 147, bgcolor: #999999"]
System Design Parameters
[/TD]

[TD="width: 118, bgcolor: #999999"]
SYS LM PER
[/TD]

[TD="width: 66, bgcolor: #999999"]

lm​

[/TD]

[TD="width: 324, bgcolor: #999999"]
Luminous flux of each LED in system design.
Note: SYS LM
PER is affected by System Optical Efficiency while LED LM is not.
[/TD]
[/TR]

[TR]

[TD="width: 118, bgcolor: #999999"]
SYS # LED
[/TD]

[TD="width: 66, bgcolor: #999999"]

​

[/TD]

[TD="width: 324, bgcolor: #999999"]
Number of LEDs needed to achieve the specified System Target
Lumens.
[/TD]
[/TR]

[TR]

[TD="width: 118, bgcolor: #999999"]
SYS W
[/TD]

[TD="width: 66, bgcolor: #999999"]

W​

[/TD]

[TD="width: 324, bgcolor: #999999"]
Power consumption of entire LED system.
Note: SYS W is
affected by System Electrical Efficiency
[/TD]
[/TR]

[TR]

[TD="width: 118, bgcolor: #999999"]
SYS LM TOT
[/TD]

[TD="width: 66, bgcolor: #999999"]

lm​

[/TD]

[TD="width: 324, bgcolor: #999999"]
Luminous flux of LED system
[/TD]
[/TR]

[TR]

[TD="width: 118, bgcolor: #999999"]
SYS LM/W
[/TD]

[TD="width: 66, bgcolor: #999999"]

lm/W​

[/TD]

[TD="width: 324, bgcolor: #999999"]
Efficacy (lumens per Watt) of LED system.
[/TD]
[/TR]

[TR]

[TD="width: 118, bgcolor: #999999"]
SYS $
[/TD]

[TD="width: 66, bgcolor: #999999"]

$​

[/TD]

[TD="width: 324, bgcolor: #999999"]
Total price of LEDs in the target LED
system.
[/TD]
[/TR]
[/TABLE]