How much is 'less than 5mW' ?

[StuM]

Originally Posted by newhaul

https://jet.com/product/detail/aeb33...FYKJfgodWGAAfA
1lumen solar pathway lights we get them here at walmart for a buck each.

Ever tried to read anything with one those things?

Yep, according to the specs given they deplete a 1 x 1.2V 350mAh battery in 8 hours and generate a single lumen.

So that's 420mWh for 8 hours or a current draw of 52.5mW. i.e. those little things still draw more than 10 times the <5mW that the OP's 12V bulb supposedly draw.

[newhaul]

Originally Posted by TrentePieds

Can one of you engineer-types give us a swift and pithy intro to the concept of the "lumen"? Its definition, its relationship to the "watt", the fact that light intensity reduces as the square of the increase in distance from source to target?

Seems to me that many of us, including the OP, could do with a quickie on those things :-)

TrentePieds

Say Google is my friend three times
How to convert lumens to watts (W)

[StuM]

Originally Posted by transmitterdan

There is no such thing as a 12V LED "bulb". The driver circuitry converts 12V supply to the voltage/current required by the LED chip. Some drivers are more efficient than others.

OK, if there is no such thing as a "bulb" what do you call those multi LED thingies, that you plug into the receptacle when you replace an incandescent bulb. They are not a diode and they are not just a chip.

Yes, I think it is feasible to get some usable light with 5mW input power from a high efficiency LED. I don't know if this particular one is truly 5mW or not. I'm just saying it is feasible. The amount of power in the visible light emitted by a single LED is a lot less than 5mW.

Until you can show me the specifications of an LED with "usable" reading light and a power consumption of 5mW or less, I will beg to differ.

I've shown plenty of specs of different small, low output LED systems, none of which come anywhere close to meeting the 5mW criterion. No one has yet been able to show actually specifications of something which does meet it.

[newhaul]

Originally Posted by StuM

Ever tried to read anything with one those things?

Yep, according to the specs given they deplete a 1 x 1.2V 350mAh battery in 8 hours and generate a single lumen.

So that's 420mWh for 8 hours or a current draw of 52.5mW. i.e. those little things still draw more than 10 times the <5mW that the OP's 12V bulb supposedly draw.

Actually yes I have read books by those little lights . Also the one lumen or 5mw im sure is the power output not power input.

[StuM]

Originally Posted by newhaul

Say Google is my friend three times
How to convert lumens to watts (W)

That gives a way to convert, but doesn't say what a lumen actually is.

A lumen is "the SI unit of luminous flux, equal to the amount of light emitted per second in a unit solid angle of one steradian from a uniform source of one candela."

Roughly:
A steradian is about 1/12 of a sphere.
A candela is about the brightness of a normal wax candle.

So VERY roughly, a lumen is about 1/12 of the total light that a candle puts out.

(This is a vast over-simplification!!!

[TrentePieds]

There you go, StuM :-) We're getting closer now. If a man is weak on the concept of "milli-" and "kilo", how's he gonna fare on the concept of "steradian"???

I think we need to come down to earth and explain plainly to him - and to me - what concepts and metrics really matter if you are engaged in determining if a light source is "good enuff"

The concept of the "watt" only matters in the evaluation of the efficacy of a light source because there's a whole lot of "stuff" subsumed in the way we banter the term about in common speech.

TrentePieds

[newhaul]

Originally Posted by TrentePieds

There you go, StuM :-) We're getting closer now. If a man is weak on the concept of "milli-" and "kilo", how's he gonna fare on the concept of "steradian"???

I think we need to come down to earth and explain plainly to him - and to me - what concepts and metrics really matter if you are engaged in determining if a light source is "good enuff"

The concept of the "watt" only matters in the evaluation of the efficacy of a light source because there's a whole lot of "stuff" subsumed in the way we banter the term about in common speech.

TrentePieds

About midway down the page is a chart that has all most of the layperson here needs or wants to know how to convert incandescent bulb wattage to lumens for led bulbs/ arrays . So they get a bulb that will produce about the amount of iridescence that they are looking for when they replace higher power usage incandescent bulbs with more efficient led bulbs/arrays.

[StuM]

Originally Posted by newhaul

About midway down the page is a chart that has all most of the layperson here needs or wants to know how to convert incandescent bulb wattage to lumens for led bulbs/ arrays . So they get a bulb that will produce about the amount of iridescence that they are looking for when they replace higher power usage incandescent bulbs with more efficient led bulbs/arrays.

Yep, and looking at the bottom chart, we see a rough equivalence:

375 lm - 25W incandescent - 6.23 W LED
and you can see that the relationship is linear.

So let's take that <5mW LED.

5mW = 6.23 W / 1246
So that's about the same as a
25/1246 = 0.02W incandescent
or 0.3 lumens.

Do you really believe those figures are reasonable for a "map reading light".
i.e.
1/3 of the output of one of those garden lights
or 1/50th of a common 1.1W flashlight bulb like this one: https://www.amazon.com/PR2-Voltage-W.../dp/B007XKX124

[newhaul]

Originally Posted by StuM

Yep, and looking at the bottom chart, we see a rough equivalence:

375 lm - 25W incandescent - 6.23 W LED
and you can see that the relationship is linear.

So let's take that <5mW LED.

5mW = 6.23 W / 1246
So that's about the same as a
25/1246 = 0.02W incandescent
or 0.3 lumens.

Do you really believe those figures are reasonable for a "map reading light".
i.e.
1/3 of the output of one of those garden lights
or 1/50th of a common 1.1W flashlight bulb like this one: https://www.amazon.com/PR2-Voltage-W.../dp/B007XKX124

OK stu first off I agree with your .3 lumen for 5mw but wow your math was even not so easy for me to follow. Here's how I did the figures .
You have 300 lumen for every 5 watts so 300 lumen times .005 watts = .3 lumen
( my math teachers couldn't even follow my math )

[duggybuggy]

Hi Bulawayo,

https://images-na.ssl-images-amazon....1V6eYEeuEL.jpg

I bought 2 of them, the idea being to use tiny consumption LEDs instead of two nightlight candles which I like to have on in the cabin throughout the whole night so that whenever I wake I immediately have the bearings of my surroundings, so these lights are ideal for that purpose.

They are not bright as such, but are very directional, so given one's eyes, map/book/chart, and lamp are all close enough together then reading is certainly possible, and without distracting the driver and a great threat to loss of nightvision, I suppose.

The only technical data I can find is that on the packet which simply says 'less than 5mW'.

The bad news is that it seems I have bought the last two in the whole world, but the good news is that I would be happy to send you one gratis if you PM your postal address. It is all enjoyment for me, and I will enjoy trying another type of LED in time to come, but mostly it would be interesting to read your assessment of its performance, but only if you are truely brutally honest. It's a good light for my prupose, so I wouldn't be offended at all, and would probably agree with you. But after all this thread it would be good for us all to have another assessment, which said it like it is. It would be my pleasure.

[newhaul]

OK now I see what light you are looking at . I have looked online at several similar and all say the same in the specs that they are 5 watts . After consideringwhat I found I would have to assume that the package yours is in is just mislabeled .
Solves the mystery for now.

[MarkJ]

Originally Posted by duggybuggy

...instead of two nightlight candles which I like to have on in the cabin throughout the whole night so that whenever I wake I immediately have the bearings of my surroundings, so these lights are ideal for that purpose.

I bought Glow in The Dark stickers from a kiss you store and stuck them on my light switches.
I can j u s t see them at night

[duggybuggy]

Hi newhaul. How about if I meter it? I am just learning how to use a multimeter. If you tell me what to do then I will do that if I'm going about it wrong. I will try and meter the amps. So I will set the meter to mA and then put the meter in line with either the positive or negative between the lamp and battery. 5 watts seems way to hi for this lamp.

[thruska]

Very interesting !
After all this is said and done about the praise of LED lighting, should we not be concerned of the light spectrum of the LED lighting ? Specifically the damage that can be done to our vision in terms of the "macular" ?
I'm no expert but I do know that the blue lights are not good for persons with macular degeneration. And the red light is great for growing lamps. If I understand correctly? natural light is the healthiest in terms of spectrum.

I would be interested in insight on these comments .
As I have had retinal detachment, and have glaucoma and macular degeneration, it would interest me.

In particular, a blue LED light would not be a good choice for me for a night light.

Thank you

[pesarsten]

Well if you want a really simple answer, 4 mw is less than 5 mw