LED Strip Lights to Lighting Spur

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Apis_Mellifera

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Hello Everyone,

I've been a browsing on here for a while now and have found lots of great tips, trick and solutions (Thanks).

However I could do with a little advice around the under-cabinet lights for a renovation project I'm undertaking.

I'd like to use LED strip lights (I'm going to rebate them into the underside of some re-purposed cabinets I have) but I can't quite work out how to wire them up. I'd like them controlled (simple on-off, no colours, no dimming) from a wall mounted light switch and would like to bury the cables into the plasterwork, which will then be tiled.

So - after careful reading through of many of the other threads on here; I've either got it sussed or am WAY out...

Please forgive and correct me if I use incorrect terminology.

The links to the lights I was planning to buy are here and here.

My understanding is:
  • (most/some) LED's require a 12v supplied through a direct current (not the 240v alternating current which is running through the ring circuit).
  • A transformer/driver will make this change in current and I need a 16W transformer (2.4m x 4.8w per m = 11.52w).
  • The circuit before the transformer will be more powerful and therfore will need thicker (2.5mm?) cables.
  • As I'm planning to run it as a spur off the main ring circuit - I should (or must?) have an Fused Connection Unit. The fuse in this unit will reduce the current from 13A to something more suitable (3A perhaps?)
Lighting.jpg


Can anyone out there provide me with a little advice?

I don't want to do anything too shocking!

Thanks in advance!
 
Cables are sized from the current (and length). Mains current before the LED driver will be extremely low. Current at 12V after the transformer will be an amp or two in your circuit.

Fuses are also based on current. In your case I guess 3A since that is the lowest.

I'll leave the FCU recommendation to those in the know.

Are the LEDs for accent or task lighting? They won't really be bright enough for task lighting, but plenty for accent lighting. Just for your reference, the quoted 360-410 lumens is highly optimistic but the total of 4.8W per metre is about right.
 
Thanks - IannIann

The lights will be used as a bit of a combo between task and accent. I have two pendant lights behind where you'll be stood at the worktop which will provide plenty of light. However I want the strips to knock out the shadow caused by those pendants (as they will be behind you) but also to highlight the tiled splash back I'm installing.
  • Do you think it would be worth going up to 24V with 685-830LM (See here)?
  • Will I encounter any issues if I use 2.5mm cable between the FCU and the lights themselves?
    • Is there an equation that I can do to get the size correct?
    • Or could/should I just use thicker than necessary?
 
You'd normally switch on the under cabinet lights via the FCU fitted under the units themselves, so why add an unnecessary light switch. Set the Leds up, see if they are sufficient for what you want, and add a second strip side by side if necessary - they can be set to go out, link at the end, and then loop backwards, but you may then need a larger transformer. There's no reason why you can't use 2.5mm, as the FCU is designed to protect a thinner cable if too much current gets drawn, but in your case, you'd be using the 3amp fuse for the transformer as well.
 
For task lighting, I'd be looking at 9.6W/m. More even if you have old eyes. Recommendations for kitchen task lighting are generally a minimum 50 foot-candles, 75-100 being preferred especially for older people. That means you would be looking at 300-600 lumens/m if 100% of the light hit your worktops (it doesn't), and realistically a bit more than that. Trust me when I say the strip you linked doesn't produce even 300 lumens/m. The 4.8W/m may be enough if the room is otherwise well lit, but you might still find you prefer the brighter strip. It can be worse in some ways to have task lighting that is insufficiently bright compared to the ambient lighting because you're eyes will be expecting even more light.

If it is acceptable stylistically, and you have enough left on the reel, the solution of doubling up the strip is a good one. Make sure your driver is also doubled in capacity, watts not volts. Try to keep the leads between the driver and strip as short as practical - 2.4m of the 9.6W/m strip would mean nearly 2 amps and you can quickly end up needing unpleasantly thick cable for any long runs. Remember the mains-level current is still tiny, that the 0.09 (amps) on your diagram.

Before you ask (:)), the 24V has nothing to do with the power of the strip. It does have practical benefits though, reducing the current flowing to and within the strip, which avoids annoying voltage drops and avoiding the LED brightness dropping along long strips.
 
Why not put in the brightest strips you can get, and use dimmable ones. Then you can adjust the brightness depending on any changing requirements.

How are you planning to fix the strips into the rebate?
 
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