Hi,
To find out the # of bulbs (any), needed to put in a room we need to know some details about the bulbs, for example; if in a certain size room I need to put in 8 ELV 50w spot lights, I would like to check that 8 lights will be enough, this information normally should be provided by the manufactorer, I looked in a the box of a new bulb, this information was not there.
Is there (anywhere) a table that will give this kind of information? or any othere source?

I looked into this briefly last year and found that it's a surprisingly difficult problem to work out how many lights you need. The professionals use fancy computer programs that take into account: wattage, number of lights, beam angle, height of ceiling, function of room (eg kitchen vs bedroom) height of working surfaces, surface finishes/reflectivity etc

One such computer program is called "Visual" from:
http://www.visuallightingsoftware.com/
They have/had a free 30 day trial version.

The problem, as you are finding, is getting the technical data for the light fittings you want to use. Some manufacturers do provide this on their web site or on CD but it seems to be only those designed for professional installation (offices, hotels etc). I couldn't find data for consumer grade lights.

The only guide I found on the web for consumer grade halogen downlights suggested this approach:

Draw a line 1M in from all the walls and put downlights on that line at roughly 1.5M intervals. Then fill in the middle at roughly 1.5M pitch. Do a layout on paper first obviously.

If in doubt I would fit more lamps at a slightly closer pitch. If they are too bright you can always drop down to 35W bulbs or fit a dimmer.

Colin

PS If you want to sound professional ask the manufacturer for "Photometric data" for their lamps

L.Spark & CWatters thanks
The thing is that you go to a customer, (this case is a real one), they say I would like 6 spot lights here and 2 there, my question; do you say that because you know that it is enough, the reply; what do you think? which i expected, now knowing the way how to calculate the lights necessary, I find that the basic data is missing.  I know that this is only a dressing room, but I beleive that if you do something you do it right or don't do it.  Of course this is not a critical situation,  and we can always find a solution, but I will try first.
I don't have the ligfhts yet but I had in mind 50W, 12V (the ELV and 8 lights is the customer's request)  

[quote author=L.Spark  link=1113290948/0#5 date=1113314379]
Having said that, most customers don't care or don't know what they want, and the contracter will have em in before they can squeak any, and are on there way to next job   [/quote]
This is exactly what I don't want to do...

Just for your information (after all, I drive you mad with this.), I went this afternoon to B&Q and looked at the 50W, 12V, halogen bulbs (spot lights), the value was on the packaging, 2100cd.

Nice one, thanks

[quote author=L.Spark  link=1113290948/0#9 date=1113346196]
As you're probably already aware, all this is a design matter, lighting designers specialise in this sort of thing, it could get quite involved & time consuming if you want to work it out perfectly you're self   [/quote]
Yep, I know