DIY Doctor

Led Bulbs, do the Ones I Want Exist?

Postby Grandad99 » Sat Mar 07, 2020 7:55 pm

Current setup is a 3 arm hanging light with 60 watt opal B22 incandescent bulbs and 2 2arm wall lights with 40 watt opal B15 bulbs. One dimmer switch for the wall lights, another for the ceiling one.

I'm trying to find LED replacements. but increasing the ceiling bulbs to 100watt as my wife has developing eyesight problems.

The only suitable ones I can find are all non-dimmable. Before getting the switch replaced I wonder of I've missed anything.
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Postby Mr White » Sat Mar 07, 2020 11:57 pm

I presume you know that you have to buy "The equivalent" of which ever watt lamp you have, so for 100w that is about 13W in LED.

I don't understand why you want a dimmable lamp when you need it to be bright.
LED lamps do not dim as well as "Old fashioned" lamps did.

You may be better off if you look for a halogen lamp.
That said you should not dim halogen lamps as it reduces their life span, also you have to de-rate most dimmers by 50%
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Postby Grandad99 » Sun Mar 08, 2020 12:51 am

Thanks.

Need it bright for reading but more restful at other times.
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Postby ericmark » Tue Mar 10, 2020 3:20 pm

60 watt bulb is considered around 800 lumen, LED max size is around 15 watt so 1300 lumen so theory should work, but in practice I found there are not direct replacements, first point is the LED sends no light towards the base, all light is directed away from base.

So in my case using E14 bulbs max size around 7 watt so around 640 lumen I used 5 watt so around 460 lumen. In one chandelier they pointed down and very poor result, other one base at bottom pointed up and reflected by white ceiling, with a far better result.

As to dimming the major problem is no colour change so no ambience, but to dim a LED means you can't use a switch mode chip to control the bulb.

The LED is a current dependent device, it needs a driver to limit the current, this is included inside the bulb, an LED can give around 100 lumen per watt, but there are losses in the driver, also in the UK we run the cables in a way which can allow a small amount of capacitive and inductive linking, so there is a small amount of power to the bulb even when switched off.

As a result the bulbs driver has to pass a little current through a bleed resistor, or capacitor to stop the bulb collecting the small amount of energy then discharging it in a flash.

So even with a switch mode power supply the bulb can not get max of 110 lumen per watt, and in real terms between 70 and 100 lumen per watt, and the bigger the bulb the less losses as does not matter if a 5 watt or 15 watt same amount of energy has to leak away.

So the cheap method to limit current with a LED is the capacitor frequency matters so designed for 50 Hz but that does not really matter, however current will vary with voltage, so tend to under drive the LED's so if voltage at max they will not fail. This control also means no problem dimming, really does not matter leading or trailing edge dimmer it will still work.

The chip control actually corrects for over or under voltage, far better use of power, but can't dim as the chip auto compensates.

There are some extra low voltage LED bulb rated DC 10 to 30 volt, since there is no capacitive or inductive coupling these can give full 110 lumen per watt, mainly used in boats and caravans. But with AC not an option.

So in the main 230 volt use a simple capacitor and the difference between dimmable and non dimmable is the amount of leakage allowed, with a dimming switch using a neutral no problem, but if not using a neutral more power needs to go through the bulb without causing it to flash, G9 bulbs are a real problem they are so small not enough room for leakage components.

So I ended up fitting an extra leakage capacitor to stop bulbs flashing.

So in real terms although an LED can be dimmed and can give more light to tungsten in real terms it often means a change in type of chandelier or switches, but some times you are lucky.

So this lamp https://cpc.farnell.com/pro-elec/pel008 ... VHEALw_wcB is claimed to dim, as it is brighter, but as to if existing dimmer will work down to 15 W I don't know, all you can do is try it.
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Postby Grandad99 » Tue Mar 10, 2020 9:03 pm

Thanks ericmark.

I think it will have to be a replacement switch and lose the dimmer facility.
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