C-Bus with LED Downlights

Hi Experts,

Does anyone install C-bus with Low Voltage LED downlights?

Most of the C-bus relay and dimmer rated in terms of current i.e 1A, 2A, 10A and 20A with 250V. But if i want to use C-bus dimmer with 12V, 10W LED downlights, Do i directly connect downlight or multiple downlights with C-bus unit? How do I calculate how much downlights one 1A channel of L5508D1A can bare?

If anyone have an idea please explain it to me.

Regards,

MC78

 

Hi,

The short answer is probably 0 LEDs per dimmer channel
The longer answer is it depends on the LED unit, whether it is dimmable and what dimming technology it supports. If you search the forums you will find a number of threads on this topic, but the general consensus is that most LED halogen replacements will typically not support dimming through standard C-Bus dimmers.

Paul

 

There is no single answer to your question. The L5508D1A is designed to dim resistive and inductive loads, not things like those retrofit LEDs.

Personally I don't see much need to dim a typical chinese retrofit LED anyway, they don't produce much usable light (LUMENS) anyway.

Furthermore, they have a similar efficiency and higher cost than halogen. And the colour is dreadful, and shifts considerably over life. Light output also drops continuously over life - eg: at 50,000 hours (if they ever last that long) the light output might be 20% what they started off with.

If you check the product specifications, you will find that a retrofit LED often produces less light (lumens) per watt than a halogen lamp. Do not get tricked my marketing hype, or unfair comparisons that specify "candelas" or "candlepower" or "lux" - the measure of light output is lumens

A 35W IRC halogen produces about 920 lumens and consumes about 38W with transformer. That's 24 lumens per system watt. So, check LED product specs carefully, and if the supplier cannot tell you, then you should look elsewhere. Don't forget that the LED wattage quoted usually doesn't include the TWO lots of control gear losses (one inside the LED, plus the original LV transformer).

So beware - there are good quality LEDs out there, but the majority (including almost all chinese ones) are complete and utter rubbish. And most LED suppliers are not known for their errr... honesty when stating product performance specifications.

 

There may be lame retrofit LEDs out there, but there are also some very good ones. Check out http://creelighting.com/downloads/CREE_LLS_LR6.pdf -- 650 lumens from 12W (better than double the efficiency of your halogens), excellent color, dimmable with clipsal dimmers, and still at 70% of output after 50K hours.

Of course there's a catch -- they're pricey.

(No, I don't work for them, just a satisfied customer.)

 

I would class CREE as one of the top suppliers out there, and they are a responsible supplier too (no lying in specs etc, even including life details at reasonable lumen depreciation rates).

But the cheap chinese thingies that most people end up using (due to price) are NOTHING like the stuff from proper lighting manufacturers like Philips, Cree, Osram, Tridonic, Vossloh, etc, etc.

--------------------

That also brings up a very important point regarding LEDs - in Lighting you must always design for end of life lumens, because lighting levels are always stipulated as minimums. For example, if the design light level was (say) minimum 300 Lux then :

For a lamp with no depreciation (halogen), you would need only 300 Lux

For a lamp with 10% depreciation (linear fluoro) you would need 333 Lux

For a lamp with 30% depreciation over life (good LED*), you would need 430 Lux

So, that quality Cree retrofit LED gives 650 Lumens but has *30% depreciation, so that makes the "design output" only 455 Lumens from 12W or 37.9 Lm/W. A 35W IRC halogen gives 920 design Lumens from about 39W, or 23.6 Lm/W.

Let's put that into perspective... to get the same light level as a 35W IRC Halogen you would use about double the number of those Cree 12W LEDS. So, for each 35W halogen you could save a total 15W using the LEDs.

The rated life of the LEDs is 50,000 hours, so over that entire lifetime you save (50,000 x 15W / 1000) 750kWh of power. At current domestic tariffs of about 20c/kWh, that equates to a saving of $150, and it's unlikely such a good quality LED package would cost only $75 each. Thus, it's not really economically viable.

And 50,000 hours is a long time - at 10 hours per day it's over 13 years before you see your $150 saving. And furthermore - what COLOUR will that LED's light be in (say) 5 or 10 years time? Who knows, but you can be sure that it will be nothing like the original colour temperature that you started out with.

So, the initial rated Lumens per Watt is one thing but, especially for LEDs, the lumen depreciation and end-of-life colour appearance are the deciding design factors. You can get excellent (rated) efficiency from LEDs if you don't care how long they last, how good the depreciation is, or what colour they are. These factors are the main reasons why LEDs are not currently viable in normal commercial lighting applications.

phew - that was a long rant

 

I thought it was one of your shorter ones

Always love reading them though John!!!