KillingTime
Newly Enlightened
I wanted a bright desk lamp for reading paperwork. The most you can buy in the UK is 100w. Nobody seems to make anything more powerful.
You can buy energy saving CFL lamps (ES27 \ BC22) that offer a direct upgrade to 150W equivalent, but the bulbs are physically larger than their incandescent counterparts,
and the bulb ends up protruding from the fitting - looks cheap.
You're looking at a standard bankers desk lamp bought from the local DIY store.
It originally took an ES27 60W bulb (circa 800 bulb lumens), it now takes a G12 CDM-T 70W warm white metal halide bulb (circa 6600 bulb lumens
.
The lamp uses external magnetic control gear with an in-built ignitor (pictured) to strike the bulb with around 5KV after which it takes 60 seconds to reach full power. HID bulbs in Europe do not have in-built ignitors (I've read they do in the USA) so, an external ignitor is required. The cabling between the gear and the lamp has to withstand the ignition pulses sent via the control gear. I used standard 3 way mains cabling (L, N + E) with the exception that the earth has its own insulation. If you use cable that has unshielded earth wire, there is insufficient insulation between the conductors to stop the ignition pulse arcing over, and the lamp does not start.
There's also a maximum length of cable you can have between the gear and the lamp, determined by the capacitance of the cable. You have to read the specification of your control gear to find out what this value is, but mine was 120pF. This worked out at around 1.5m for the cable I used. Used a Fluke 185 DMM to check the capacitance.
I used magnetic control gear because the unit was readily available and cheap (£30 GBP - screwfix) and came in a shielded / earthed enclosure. The downside to using magnetic control gear is that the bulb is sometimes over driven resulting in shorter life, and the switching frequency is fixed to your mains supply (50HZ in the UK). Some people claim to be able to see the 50Hz flicker from the HID lamp. I have to say, on some occasions, when not looking directly at the lamp, I could detect a slight flicker out the corner of my eye, but it was very slight, and it doesn't bother me. Some people are affected more than others though...
The more modern electronic ballasts use a higher switching frequency, but are also more costly (£80 GBP), and they don't come in an enclosure, you have to buy this as an extra, with all the cable glands, chassis fuses etc...
Some notes to anyone wishing to do this mod:
1. The reflector between the bulb and the glass shade was made in-house (DIY) out of aluminium strip \ sheet. You need this because the lamp is so bright, even with the green glass shade I found it uncomfortable to look at the shade from above. The glass shade also gets hot without the alu shield, you could burn yourself.
2. The bulb I used was a Philips MasterColour CDM-T 70W 830 (warm white). The original lamp fitting was rated for 60W, so I'm breaching this by 10W, but I added the alu shield. It worked for me.
3. The above bulb has a UV stop built into it. Not all metal halide bulbs have this. Check the spec first if you don't use the same bulb, or you could blind yourself.
4. Not all external control gear has the ability to perform a hot re-strike of the bulb (mine doesn't). This means you have to wait 10 mins after you've turned the lamp off, to turn it back on again. Even if you did find a ballast that claims to offer hot re-strike, I'm not sure it would work with this type of lamp fitting. In order to succeed with a hot re-strike you need a very high voltage to overcome the increased resistance between the electrode terminals while the bulb is hot and under increased gas pressure. In order to get the higher than normal strike voltage to the bulb, you need wiring that can handle the voltage. That's where the problem lies. I was limited to my cable choice when I re-wired the lamp, because once the wire enters the desk lamp fitting, you have to thread it through the internal pipe work that makes up the actual lamp fitting. Take a look that size of cabling that comes with external control gear , it was 12mm diameter on my box. I suspect this is because of the increased insulation, but the most I could thread through the lamp fitting was two 1mm sq cables (with insulation). The hot re-strike voltage would just arc over. You could overcome this by taking the thick cable directly to the bulb holder terminals, but it would look ugly on a bankers desk lamp, I wanted to keep it looking normal from the outside.
5. Earthing. You need to earth your metal lamp fitting if it carries mains voltage and especially if it's going to carry the ignition pulses to strike the lamp. My lamp was made of metal, and came with a declaration that it was double earthed, meaning there was no need to earth it (it wasn't earthed)? So I added an earth connection to the lamp chassis.
6. I noticed that this type of bulb emits nearly all of its light perpendicular to the glass envelope, and not from the very end of the bulb. In this respect, it's ideally suited to the way it's mounted in the bankers lamp housing. If you wanted to retrofit an angle poise lamp for instance, and keep the same mounting point for the G12 bulb holder, you'd have to look for a different bulb because most of the light would hit the sides of the lamp shade instead of making it out of the front of the lamp shade. I did actually try what I've just described with an angle poise and I abandoned the project in favour of the bankers lamp when I realised the mistake I'd made. If you want to do an angle poise lamp, you could perhaps look at the Osram Powerstar HQI-T 70W. It comes with the same base (G12), can be used with the same control gear (most cases - check) but has its metal halide glass envelope at the end of the bulb instead of the middle. Looks promising.
You can buy energy saving CFL lamps (ES27 \ BC22) that offer a direct upgrade to 150W equivalent, but the bulbs are physically larger than their incandescent counterparts,
and the bulb ends up protruding from the fitting - looks cheap.
You're looking at a standard bankers desk lamp bought from the local DIY store.
It originally took an ES27 60W bulb (circa 800 bulb lumens), it now takes a G12 CDM-T 70W warm white metal halide bulb (circa 6600 bulb lumens
.The lamp uses external magnetic control gear with an in-built ignitor (pictured) to strike the bulb with around 5KV after which it takes 60 seconds to reach full power. HID bulbs in Europe do not have in-built ignitors (I've read they do in the USA) so, an external ignitor is required. The cabling between the gear and the lamp has to withstand the ignition pulses sent via the control gear. I used standard 3 way mains cabling (L, N + E) with the exception that the earth has its own insulation. If you use cable that has unshielded earth wire, there is insufficient insulation between the conductors to stop the ignition pulse arcing over, and the lamp does not start.
There's also a maximum length of cable you can have between the gear and the lamp, determined by the capacitance of the cable. You have to read the specification of your control gear to find out what this value is, but mine was 120pF. This worked out at around 1.5m for the cable I used. Used a Fluke 185 DMM to check the capacitance.
I used magnetic control gear because the unit was readily available and cheap (£30 GBP - screwfix) and came in a shielded / earthed enclosure. The downside to using magnetic control gear is that the bulb is sometimes over driven resulting in shorter life, and the switching frequency is fixed to your mains supply (50HZ in the UK). Some people claim to be able to see the 50Hz flicker from the HID lamp. I have to say, on some occasions, when not looking directly at the lamp, I could detect a slight flicker out the corner of my eye, but it was very slight, and it doesn't bother me. Some people are affected more than others though...
The more modern electronic ballasts use a higher switching frequency, but are also more costly (£80 GBP), and they don't come in an enclosure, you have to buy this as an extra, with all the cable glands, chassis fuses etc...
Some notes to anyone wishing to do this mod:
1. The reflector between the bulb and the glass shade was made in-house (DIY) out of aluminium strip \ sheet. You need this because the lamp is so bright, even with the green glass shade I found it uncomfortable to look at the shade from above. The glass shade also gets hot without the alu shield, you could burn yourself.
2. The bulb I used was a Philips MasterColour CDM-T 70W 830 (warm white). The original lamp fitting was rated for 60W, so I'm breaching this by 10W, but I added the alu shield. It worked for me.
3. The above bulb has a UV stop built into it. Not all metal halide bulbs have this. Check the spec first if you don't use the same bulb, or you could blind yourself.
4. Not all external control gear has the ability to perform a hot re-strike of the bulb (mine doesn't). This means you have to wait 10 mins after you've turned the lamp off, to turn it back on again. Even if you did find a ballast that claims to offer hot re-strike, I'm not sure it would work with this type of lamp fitting. In order to succeed with a hot re-strike you need a very high voltage to overcome the increased resistance between the electrode terminals while the bulb is hot and under increased gas pressure. In order to get the higher than normal strike voltage to the bulb, you need wiring that can handle the voltage. That's where the problem lies. I was limited to my cable choice when I re-wired the lamp, because once the wire enters the desk lamp fitting, you have to thread it through the internal pipe work that makes up the actual lamp fitting. Take a look that size of cabling that comes with external control gear , it was 12mm diameter on my box. I suspect this is because of the increased insulation, but the most I could thread through the lamp fitting was two 1mm sq cables (with insulation). The hot re-strike voltage would just arc over. You could overcome this by taking the thick cable directly to the bulb holder terminals, but it would look ugly on a bankers desk lamp, I wanted to keep it looking normal from the outside.
5. Earthing. You need to earth your metal lamp fitting if it carries mains voltage and especially if it's going to carry the ignition pulses to strike the lamp. My lamp was made of metal, and came with a declaration that it was double earthed, meaning there was no need to earth it (it wasn't earthed)? So I added an earth connection to the lamp chassis.
6. I noticed that this type of bulb emits nearly all of its light perpendicular to the glass envelope, and not from the very end of the bulb. In this respect, it's ideally suited to the way it's mounted in the bankers lamp housing. If you wanted to retrofit an angle poise lamp for instance, and keep the same mounting point for the G12 bulb holder, you'd have to look for a different bulb because most of the light would hit the sides of the lamp shade instead of making it out of the front of the lamp shade. I did actually try what I've just described with an angle poise and I abandoned the project in favour of the bankers lamp when I realised the mistake I'd made. If you want to do an angle poise lamp, you could perhaps look at the Osram Powerstar HQI-T 70W. It comes with the same base (G12), can be used with the same control gear (most cases - check) but has its metal halide glass envelope at the end of the bulb instead of the middle. Looks promising.
but just make sure you're safe.
