How many Downlights and a few other related questions?

[markf]

Hi,

I have a room measuring 7m long, 3.5m wide at one end and 1.8m wide at the other (I know it is an unusual wedge shape). I am looking at installing low voltage downlighters and splitting the room into two sets of lights both controlled from a 2-gang dimmer. However I have some questions I hope somebody could help me with:-

1) How many downlighters would be needed to adequately cover the room - I wish to use 50w lamps with a 36 degree angle (I reckon about 12 but am not too sure)

2) I will be looking at using one transformer per light so what is the best way to connect each transformer to the switched live - loop in and out of transformer or take a feed for several transformers from a joint box?

3) Above the ceiling will be roof space insulation (with no access to the roof space as it is a single storey extension, but the cabling will be done prior to a new ceiling being fitted) so are there any precautions I should take regarding airflow or heat build-up around the transformer/light head?

4) The only lights to be run from the MCB will be the two sets of downlights and three wall lights. What rating of MCB will I need to use to avoid nuisance tripping?

5) Would it be better to use 50w 240v halogen downlights in this case, and if so how will this effect questions 1 to 4?

I would normally ask these questions at the time of purchase, but you never know if the retailer will give good/correct/honest advice - I have been bitten in this respect before.

Many thanks in advance
Mark

 

[breezer]

have the mains ones, cheaper, less hassle and 12 of them, you can always dim them, but once done cant add more (that's my opinion)

 

[salem2000]

Mains is the best idea. A lot cheaper than 12v and less work.

Paid approx £12.00each with lamp, from TLC Direct for my hall.

 

[Albert]

I have a room measuring 7m long, 3.5m wide at one end and 1.8m wide at the other (I know it is an unusual wedge shape). I am looking at installing low voltage downlighters and splitting the room into two sets of lights both controlled from a 2-gang dimmer. However I have some questions I hope somebody could help me with:-

I must agree, I have rewired my house and put in about 100 (all together) spot lights 50W each, all main, very simple and much cheaper.
Just one advise if you intend to put in 12 x 50W, you will need to consider your dimmer to be capable of carrying the load, good luck.

Albert

 

[markf]

Thanks guys - looks like the 240v version sounds the way to go.

Just one more question - do I need to concern myself with heat from the lamp when there will be insulation behind the ceiling?

 

[breezer]

yes, move the insulation, i read some where some one mentioned putting an earthen ware flower pot over lamp, also pointed out was although hole for cable good, it also concentrates heat output

 

[BR]

yes i agree, the disadvantages far outweigh the advantages of using ELV down lighters in domestic installations. As regards MCB 6A is adequate.

 

[evdama]

Just to put a fly in the chardonnay;
Two (independant) people at work both curse their 240v setups and covet someone elses 12v systems.
They both say the bulbs dont last very long.
A visit to the lightbulb stand while shopping at Tescos the other day seemed to qualify this.The phillips brands are guaranteed longer on the 12v than on the 240v.

I beleive its a maximum of twelve 100w fittings for each 6A MCB on the consumer unit.

 

[BR]

Current = watts / voltage (for which you take 230V)

12 X 100 = 1200

1200 / 230 = 5.2A

So yes this is good advice, leaving a reasonable tolerance.

Yes, mains voltage halogen tend to blow quicker but if they are installed correctly this should not be unreasonable. Buying 240V rated good brand lamps also helps.

 

[kendor]

You could incorporate a soft starter this would increase the life of your lamps see here

This would be alright if you were to ditch your dimmer switches

another way would be for a ramp circuit 0-10v controlling an analogue input dimmer module

I have built these ramp circuits for work the first about 5 years ago and the lamps on those circuits have never blown so far.

 

[Big_Spark]

Well Kendor, it would appear that we agree on something afterall as I fully concur with your comments..although I bet the lamps you used at work are decent ones not the cheapies most people buy for their house!

 

[securespark]

I'm going to put my OSRAM hat on again!!

They're super, spiffing, marvellous, tickety-boo, champion, top-hole etcetera, etcetera, etcetera.......

 

[kendor]

I bet the lamps you used at work are decent ones not the cheapies most people buy for their house!

Yes you are quite right, they are of "broadcast" quality regarding colour temperature specifications and very expensive but the soft start systems seem to work really well, at an average cost of £200 per lamp a reliable system is definitely needed.
The quoted £12 per halogen lamp for home use would certainly worry me if by experience people are saying they only last a short time.

The initial outlay hopefully in the long run would be recouped and with the additional advantages of having automatic as well as remote control dimming functionality easily added, must be a bonus.

 

[salem2000]

The quoted £12 per halogen lamp for home use would certainly worry me if by experience people are saying they only last a short time.

The fittings & Lamps I used have been going for over 14-15 months now. How long do people expect lamps to last. If you by your lamps from your local supermarket of diy own brand, what do you expect. You DO get what you pay for and if you pay peanuts, expect something built by monkeys.

What do you guys think about the life span of Halogen lamps, I've seen cheap ones pop after an hour.

 

[il78]

I get mine for 80p each and last around 4-5months......bit of a bargain.......