Machine Tool Task Light

[John ShepherdParticipant @johnshepherd38883]

I was looking forward to the article on lighting in the latest issue of MEW as I need to update mine, but a clip on work light and some dubious costings on how much it costs to run hardly warrants an article. (surely it is better to know how much it costs per hour than how much it might cost if it lasts its expected life).

The article and the attached table indicates that the 3W LED gives less illumination than a 1W version but there is no explanation as to why. It would be interesting to know why this is.

I don't want to have a go at the author, at least he has made an effort to submit something but I am afraid it is not up to the usual standard of MEW.

If nothing else it has spurred me on to do something I have been meaning to do for some time. That is to measure the output of CFL lamps to see how the claims to be equivalent to a much higher wattage incandescent match up.

[John ShepherdParticipant @johnshepherd38883]

[David LittlewoodParticipant @davidlittlewood51847]

I think the article quite clearly did produce a cost per hour figure, so I can't agree with that criticism. I did however have two concerns about it. First, he appears to have accepted the power rating of the bulbs as being the same as the power consumption of the unit. This may be close to the truth with the incandescent bulbs, but may be far from true for the LED ones, where the transformer may dissipate more than the lights. Any article with pretensions to accuracy should have measured the power consumption; plug in power meters are cheap enough.

Second, I always feel concerned when writers mis-quote unit designations. Mr Theasby, the unit for energy you were using should be written kWh; in the article it was variously written as Kw/H and KW/h. The / means "per", and kW per hour, though it does exist as a meaningful unit, is NOT energy (it is in fact a ramp rate, the rate of change of power flows, well known to National Grid). The symbol W for watts is always capitalised (but the name is not); the symbol k for kilo (10^3) is always lower case (an exception to the general rule that increasers – M, G, T etc are upper case, and reducers are lower case) and the symbol h for hour is always lower case. There should also be a space between the number and the unit designation.

This may seem like nit-picking, but the standard methods exist in the SI system to minimise confusion and maximise rapid comprehension; if you are forever having to stop and work out what an author means it does not make for easy comprehension.

David

Edited By David Littlewood on 09/02/2013 18:21:07

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