Unfortunately I don’t think that it’s possible for Tenebrae. I tried it. My eyes couldn’t see anything, and we were doing it in the morning, so the light was coming in, but it was so dark I couldn’t read anything during Lauds. If everyone has the full office memorized, great, but that’s not realistic.

The priest at the altar has enough candles and such that it usually works out for the Rorate Mass, since he ought not to need to read anything for large portions (hopefully he has the Mass memorized well enough to do so).

The trick for the schola is that you need to place candles under and not just to the side of the stand in order to avoid too many shadows (the priest could do this too, but he probably can get away without it, and if you use the TLM, with altar cards, you can’t do this at the middle anyway).

But I really abhor the schola using candles unless you put everything out such that they don’t need the book. It’s a disaster waiting to happen. Someone spills every time that we have candles, and they aren’t ever the ones who scrape off the wax. We now have book lights, and I’m not going to out trad Canon Huberfeld of the ICRSP in Wausau, Wisconsin, one of the most trad priests that I know. He allows book lights at Tenebrae, and that’s that for me.

At Tenebrae, we gradually kill the electric lights, leaving the ones in the porch on. Even with those on the church is almost pitch black as we do this in the late evening. We have started to give the choir 'in choir' small candles, that get put out during the Miserere, depending on how much has been memorised by the choir member.

I saw one photo and it looked very good.

Have sung at several rotate masses that were entirely candlelit. In the choir loft we just had small book lights.

The congregation brought their own candles to hold and the priest delegated the lighting of the sanctuary to people competent in that.

There will be a lot of melted wax cleanup.

Also don’t recommend using candles in the choir loft as a light source. Had a girl try to use her Easter vigil candle as a light, ended up starting the cardboard drip holder on fire in the middle of singing a polyphonic Kyrie. The choir director tried to blow it out while directing, which didn’t work, and the girl panicked and threw the burning cardboard on the carpeted floor. The important thing is we didn’t miss a note.

We do tenebrae just with low electric lights, and the ceremonial candles in the sanctuary. We do Rorate and Christmas Midnight actually by candlelight. It is entirely possible to sing a candlelit only Mass, including in the choir loft, it is just more work and less convenient than electric lighting. I would not advocate for holding candles and music books at the same time, but either holding your book next to a candelabra (which shouldn't have to be "fixed" to anything if the singers are being responsible and conscious of the potential hazard) or holding a candle while reading from a music stand are both quite possible. I believe that if candles fall to the ground, they will not catch a wooden floor on fire, they will just make an unpleasant noise upon contact, extinguish themselves, and spill a great mess of melted wax. Depending on how you weigh the scales, this inconvenience and risk may be worthwhile for a truly candlelit Mass. We can achieve adequate lighting in our loft by using a few carefully positioned candelabrae; these have their candles sitting at about eye level, and most have seven candles (some five).

" if the singers are being responsible and conscious of the potential hazard"

All it takes is an involuntary muscle spasm from one person, and fire from flame cannot always be safely controlled (with candles at eye level, flames in motion can end up touching hair, skin, and clothing, not to mention paper, in closely spaced choristers in a relatively compact space before the flames extinguish upon final impact). Count yourselves lucky if a risk has not yet given sad fruit; but it's better to plan for greater safety. That's not safetyism but just critical thinking rather than magical thinking. Failure to do that could be considered reckless enough, depending on the particular circumstances, that it amounts to gross negligence that an insurance company could use to deny coverage for liability claims.

We found candelabras on very steady stands away from us in the center aisles but higher than us seated worked the best. We have dozens of them so it was easy to set them up in many places. That way no one needed to hold a candle, and you get a good light source thats concentrated.

We also place some reflective metals underneath which help make more light.

(which shouldn't have to be "fixed" to anything if the singers are being responsible and conscious of the potential hazard)

I am told by someone that I ought to trust (and I do, it's just annoying that this is the advice) that I have too-high expectations of adults. Or rather, I should have high standards but understand that people really don't always have them of themselves. So Liam's point stands. Never mind true accidents wherein someone does something involuntary.

We have found that candles cast more light when they are up above than when they are placed at eye level.

Parker devices are work well to light individual singers’s music stands.

@davido What is a parker device?

The booklights that I have singers use in those situations have an "orange" setting to them which are close enough to candle light to avoid distracting the people.

These are cardboard circles with a small hole in the middle, with small score lines so that a candle can be forced through and be held.
https://stpauls.org.uk/box-of-200-drip-shields.html
This may also be an idea,
https://stpauls.org.uk/individual-reusable-plastic-drip-lantern-clear.html

If the candle is the right size and the cardboard new, it works. But if it is not held by the cardboard tightly it will slip. You could use an elastic band around the candle then it won't slip.
Also you will need a reasonable amount of book to hold it, although the processions are all in the centre so plenty of unused pages left to hold the cardboard. My Graduale has think boards as part of its binding so they help.

I found the cardboard holders can grip the candle so well that the edge of the cardboard can be slipped into a Graduale, and will hold the candle at an ideal distance. We have regularly processed and sung at Candlemas with no problems

This is what started the fire in our choir loft.

One may also want to consult the insurance policy of the church...

https://www.amazon.com/Gritin-Rechargeable-Temperatures-Brightness-Lightweight/dp/B0BGN9R72N/ref=asc_df_B0BGN9R72N?mcid=7e02bf91fd373f688b3cc8230b533bb0&hvocijid=6650643213210815737-B0BGN9R72N-&hvexpln=73&tag=hyprod-20&linkCode=df0&hvadid=721245378154&hvpos=&hvnetw=g&hvrand=6650643213210815737&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9019615&hvtargid=pla-2281435179338&th=1

Here are our book lights. There are other similar ones available from the same company.

Pic