Spotlights and dimmers

[gregbbb]

Hi

I am replacing 2 standard lights (blub/shade) with 2 spotlight units (4 lights on each) and also replacing the standard 2 gang light switch that controls them with a 2 gang dimmer.

Now, the spotlights say the can handle up to 75W on each bulb (300W per unit) and the 2 gang dimmer switch has 200W marked on each gang. So, my question is what is the maximum bulb rating I can use on the spotlights?

I'm guessing 4 x 50W bulbs = 200W = rating on dimmer. Is this wise to exactly match the maximum rating on the dimmer?

I did read somewhere about doubling the rating.

Any advice, as always, is much appreciated.

Cheers

 

[Adam_151]

with halogen lamps its adviseable to size the dimmer to at least double the rating of the lamps you are going to connect to

(its to do with the fact that they run hotter than normal lamps, and as they will have the same working resistance as a non halogen lamp of the same rateing which is working at a lower temperature, it naturally follows that the cold resistace must be lower than than the none halogen lamp, which leads to a higher transisant surge current when the lamp is first switched on, which can sometimes cause the triac in the dimmer to fail)

As well as startup, passing say around 10% of full power into a lamp is also stressfull for a dimmer, its passing many times the full current (because the lamp is cooler and therefore more conductive than when its running at full temperature ) but only for 10% of the time (and the triacs don't see it as balencing out, they just don't like it)*

*Dimming a halogen lamp will also reduce lamp life, but thats another story altogether

Dimmers are rated to handle the particulars of ordinary lamps, but because of the lower cold impedances associated with halogen lamps, the doubling rule of thumb is applied

 

[Steve]

erm . . . adam, tell me where bashdem mentioned halogen lamps . . .

 

[Adam_151]

erm . . . adam, tell me where bashdem mentioned halogen lamps . . .

I suppose he didn't but I naturally assumed GU10 halogen recessed spot fittings, that would be the most likely thing for him to be fitting, expessially as he didn't meantion a transformer...

 

[gregbbb]

Sorry, I forgot to mention, its 2 lots of these I am fitting...

http://www.nextdaylighting.com/ItmDtls.asp?ItmCd=125924

Have since found out the dimmer is in fax 250W max per switch, this needs to be halved as mentioned in the instructions (small print). So I'm looking at 125W to cover 4 spotlights.

So now I'm looking for 25W or 30W GU10 spotlight bulbs.

 

[Adam_151]

don't beleive 25W or 30W are available, 35w certainly is, and I can't imagine that going to 56% of the rating instead of 50% is going to be too bad..., afterall there should be a margin of error. Or you could use those LED GU10s

 

[gregbbb]

Would 35W bulbs be particularly dim? Are they comparable to normal incandescent light bulbs with regards to wattage?

For example where I am to replace 1 60W incandescant bulb with 4 x 35W halogen spotlight bulbs will I end up with nearly double as much light - trying not to be ignorant here but would rather get a new dimmer than put up with poor lighting just to satisfy the dimmer rating.

Cheers

 

[philrosenberg]

May be better for your home's next owner too if you put a higher rater dimmer in.
Once you sell the place the next owner isn't going to know that the dimmer is only rated to 125W, he/she will just see the 50W rating on the lamp fitting and will probably use these when the bulbs blow.

I think it would just make things feel a little more professional if it all adds up.

 

[Steve]

bashdem, its you again i see!

see my recommendation on your OTHER thread discussing the same topic